17β-estradiol or estradiol

The primary type of estrogen that is secreted by the ovary.

5α-reductase

An enzyme that converts testosterone into dihydrotestosterone (DHT).

5-HT

See serotonin.

A1

See primary auditory cortex.

absence attack

See simple partial seizure.

absolute refractory phase

A brief period of complete insensitivity to stimuli.

accommodation

The process of focusing by the ciliary muscles and the lens to form a sharp image on the retina.

acetylcholine (ACh)

A neurotransmitter produced and released by parasympathetic postganglionic neurons, by motor neurons, and by neurons throughout the brain.

acetylcholinesterase (AChE)

An enzyme that inactivates the transmitter acetylcholine both at synaptic sites and elsewhere in the nervous system.

ACh

See acetylcholine.

AChE

See acetylcholinesterase.

acid

See LSD.

ACTH

See adrenocorticotropic hormone.

actin

A protein that, along with myosin, mediates the contraction of muscle fibers.

action potential

The propagated electrical message of a neuron that travels along the axon to the presynaptic axon terminals.

activational effect

A temporary change in behavior resulting from the administration of a hormone to an adult animal.

acupuncture

The insertion of needles at designated points on the skin in an attempt to alleviate pain or physiological malfunction, or alter behavior.

adaptation

1. A trait that increases the probability that an individual will leave offspring in subsequent generations.

addiction

See dependence.

adenohypophysis

See anterior pituitary.

adenosine

An endogenous neuromodulator that generally reduces neural activity. Caffeine interferes with adenosine binding. In the context of neural transmission, adenosine alters synaptic activity.

adequate stimulus

The type of stimulus for which a given sensory organ is particularly adapted.

Aδfiber

A moderately large, myelinated, and therefore fast-conducting axon, usually transmitting pain information.

ADH

See arginine vasopressin.

ADHD

See attention deficit hyperactivity disorder.

adipose tissue

Tissue made up of fat cells.

adrenal cortex

The outer rind of the adrenal gland, which secretes steroid hormones, including cortisol.

adrenal gland

An endocrine gland atop the kidney.

adrenal medulla

The inner core of the adrenal gland, which secretes epinephrine and norepinephrine.

adrenaline

See epinephrine.

adrenocorticoids

Also called adrenal steroids. A class of steroid hormones that are secreted by the adrenal cortex, including glucocorticoids such as cortisol and mineralocorticoids such as aldosterone.

adrenocorticotropic hormone (ACTH)

A tropic hormone secreted by the anterior pituitary gland that controls the production and release of hormones of the adrenal cortex.

adult neurogenesis

The creation of new neurons in the brain of an adult.

afferent

In reference to axons, carrying action potentials from a sensory organ to the central nervous system or from one region to another region of interest. Compare efferent.

affinity

See binding affinity.

afterpotential

The positive or negative change in membrane potential that may follow an action potential.

agnosia

The inability to recognize objects, despite being able to describe them in terms of form and color. It may occur after localized brain damage.

agonist

A molecule, usually a drug, that binds a receptor molecule and initiates a response like that of another molecule, usually a neurotransmitter.

agraphia

The inability to write.

AIS

See androgen insensitivity syndrome.

alarm reaction

The initial response to stress.

aldosterone

A mineralocorticoid hormone, a steroid secreted by the adrenal cortex, that induces the kidneys to conserve sodium ions.

alexia

The inability to read.

allele

One of two or more versions of a given gene or genetic locus. Different alleles may differ in the functionality of the protein produced.

allocortex

Cortical tissue with three layers or unlayered organization, in contrast with six-layered neocortex.

allomone

A chemical signal that is released outside the body by one species and affects the behavior of other species.

allopregnanolone

A naturally occurring steroid that modulates GABA receptor activity in much the same way that benzodiazepine anxiolytics do.

all-or-none property

The fact that the amplitude of the action potential is independent of the magnitude of the stimulus.

allostasis

A coordinated set of behavioral and physiological changes to maintain homeostasis.

α-fetoprotein

A protein found in the plasma of fetuses. In rodents, α-fetoprotein binds estrogens and prevents them from entering the brain.

α-melanocyte-stimulating hormone (α-MSH)

A peptide that binds the melanocortin receptor.

alpha motor neuron

A motor neuron that controls the main contractile fibers (extrafusal fibers) of a muscle.

α--MSH

See α-melanocyte-stimulating hormone.

alpha rhythm

A brain potential of 8– 12 Hz that occurs during relaxed wakefulness.

α--synuclein

A protein that has been implicated in Parkinson’s disease.

ALS

See amyotrophic lateral sclerosis.

altricial

Referring to animals that are born in an undeveloped state and depend on maternal care, as human infants do.

Alzheimer’s disease

A form of dementia that may appear in middle age but is more frequent among the aged.

amacrine cells

Specialized retinal neurons that contact both the bipolar cells and the ganglion cells and are especially significant in inhibitory interactions within the retina.

amblyopia

Reduced visual acuity of one eye, that is not caused by optical or retinal impairments.

AMH

See anti-m&umml;llerian hormone.

amine hormones

Also called monoamine hormones. A class of hormones, each composed of a single amino acid that has been modified into a related molecule, such as melatonin or epinephrine.

amine neurotransmitter

A neurotransmitter based on modifications of a single amino acid. Examples include acetylcholine, serotonin, and dopamine.

amino acid neurotransmitter

A neurotransmitter that is itself an amino acid. Examples include GABA, glycine, and glutamate.

amnesia

Severe impairment of memory.

AMPA receptor

A glutamate receptor that also binds the glutamate agonist AMPA.

amphetamine

A molecule that resembles the structure of the catecholamine transmitters and enhances their activity.

amphetamine psychosis

A delusional and psychotic state, closely resembling acute schizophrenia, that is brought on by repeated use of high doses of amphetamine.

amplitude

Magnitude or strength. In acoustics, the force sound exerts per unit area, usually measured as dynes per square centimeter.

ampulla

An enlarged region of each semicircular canal that contains the receptor cells (hair cells) of the vestibular system.

amusia

A disorder characterized by the inability to discern tunes accurately.

amygdala

A group of nuclei in the medial anterior part of the temporal lobe.

amyloid plaques

See senile plaques.

amyloid precursor protein (APP)

A protein that, when cleaved by several enzymes, produces β-amyloid.

amyotrophic lateral sclerosis (ALS)

Also called Lou Gehrig’s disease. A disease in which motor neurons and their target muscles waste away.

analgesia

Absence of or reduction in pain.

analgesic

Referring to painkilling properties.

analogy

Similarity of function, although the structures of interest may look different. The human hand and an elephant’s trunk are analogous features.

anandamide

An endogenous substance that binds the cannabinoid receptor molecule.

androgen insensitivity syndrome (AIS)

A syndrome caused by a mutation of the androgen receptor gene that renders tissues insensitive to androgenic hormones like testosterone. Affected XY individuals are phenotypic females, but they have internal testes and regressed internal genital structures.

androgens

A class of hormones that includes testosterone and other male hormones.

androstenedione

The chief sex hormone secreted by the human adrenal cortex.

angel dust

See phencyclidine.

angiography

A brain-imaging technique in which a specialized X-ray image of the head is taken shortly after the cerebral blood vessels have been filled with a radiopaque dye by means of a catheter.

angiotensin II

A substance that is produced in the blood by the action of renin and that may play a role in the control of thirst.

angular gyrus

A brain region in which strokes can lead to word blindness.

anion

A negatively charged ion, such as a protein or chloride ion.

annulospiral ending

See primary sensory ending.

anomia

The inability to name persons or objects readily.

anorexia nervosa

A syndrome in which individuals severely deprive themselves of food.

anorexigenic neurons

Neurons of the hypothalamic appetite system that inhibit feeding behavior.

anosmia

The inability to smell.

anosognosia

Denial of illness.

ANP

See atrial natriuretic peptide.

antagonist

1. A molecule, usually a drug, that interferes with or prevents the action of a transmitter. 2. A muscle that counteracts the effect of another muscle.

anterior

Also called rostral. In anatomy, toward the head end of an organism. Compare posterior.

anterior cerebral arteries

Two large arteries, arising from the internal carotid arteries, that provide blood to the anterior poles and medial surfaces of the cerebral hemispheres.

anterior pituitary

Also called adenohypophysis. The front division of the pituitary gland. It secretes tropic hormones.

anterograde amnesia

The inability to form new memories beginning with the onset of a disorder.

anterograde degeneration

Also called Wallerian degeneration. The loss of the distal portion of an axon resulting from injury to the axon.

anterolateral system or spinothalamic system

A somatosensory system that carries most of the pain and temperature information from the body to the brain.

antibody

Also called immunoglobulin. A large protein that recognizes and permanently binds to particular shapes, normally as part of the immune system attack on foreign particles.

antidepressants

A class of drugs that relieve the symptoms of depression.

antidiuretic hormone (ADH)

See arginine vasopressin.

anti-m&umml;llerian hormone (AMH)

A protein hormone secreted by the fetal testis that inhibits m&umml;llerian duct development.

antipsychotics

Also called neuroleptics. A class of drugs that alleviate the symptoms of schizophrenia, typically by blocking dopamine receptors.

anxiety disorder

Any of a class of psychological disorders that include recurrent panic states and generalized anxiety disorders.

anxiolytics

A class of substances that are used to combat anxiety. Examples include alcohol, opiates, barbiturates, and the benzodiazepines.

aphagia

Refusal to eat.

aphasia

An impairment in language understanding and/or production that is caused by brain injury.

apical dendrite

The type of dendrite that extends from a pyramidal cell to the outermost surface of the cortex.

apolipoprotein E (ApoE)

A protein that may help break down amyloid.

apoptosis

See cell death.

APP

See amyloid precursor protein.

appetitive behavior

The second stage of mating behavior. It helps establish or maintain sexual interaction.

apraxia

An impairment in the ability to begin and execute skilled voluntary movements, even though there is no muscle paralysis.

aquaporins

Channels spanning the cell membrane that are specialized for conducting water molecules into or out of the cell.

arachnoid

The thin covering (one of the three meninges) of the brain that lies between the dura mater and pia mater.

arborization

The elaborate branching of the dendrites of some neurons.

arcuate fasciculus

A tract believed by some to connect Wernicke’s area to Broca’s area.

arcuate nucleus

An arc-shaped hypothalamic nucleus implicated in appetite control.

area 17

See primary visual cortex.

arginine vasopressin (AVP)

Also called vasopressin or antidiuretic hormone (ADH). A peptide hormone from the posterior pituitary that promotes water conservation.

aromatase

An enzyme that converts some androgens into estrogens.

aromatization

The chemical reaction that converts testosterone to estradiol, and other androgens to other estrogens.

aromatization hypothesis

The hypothesis that testicular androgens enter the brain and are converted there into estrogens to masculinize the developing nervous system in some rodents.

arousal

The global, nonselective level of alertness of an individual.

ASD

See autism spectrum disorder.

aspartate

An amino acid transmitter that is excitatory at many synapses.

associative learning

A type of learning in which an association is formed between two stimuli or between a stimulus and a response. It includes both classical and operant conditioning.

astereognosis

The inability to recognize objects by touching and feeling them.

astrocyte

A star-shaped glial cell with numerous processes (extensions) that run in all directions.

ataxia

An impairment in the direction, extent, and rate of muscular movement. It is often caused by cerebellar pathology.

atrial natriuretic peptide (ANP)

A hormone, secreted by the heart, that normally reduces blood pressure, inhibits drinking, and promotes the excretion of water and salt at the kidneys.

attention

Also called selective attention. A state or condition of selective awareness or perceptual receptivity, by which specific stimuli are selected for enhanced processing.

attention deficit hyperactivity disorder (ADHD)

Syndrome of distractibility, impulsiveness, and hyperactivity that, in children, interferes with school performance.

attentional bottleneck

A filter that results from the limits intrinsic to our attentional processes, with the result that only the most important stimuli are selected for special processing.

attentional spotlight

The shifting of our limited selective attention around the environment to highlight stimuli for enhanced processing.

atypical antipsychotics

Also called atypical neuroleptics. A class of antischizophrenic drugs that have actions other than or in addition to the dopamine D2 receptor antagonism that characterizes the typical antipsychotics.

aura

In epilepsy, the unusual sensations or premonition that may precede the beginning of a seizure.

australopithecine

Referring to Australopithecus, a primate genus, known only from the fossil record, thought to be an ancestor to humans.

autism spectrum disorder (ASD)

A disorder, which can run from mild to severe, characterized by deficits in social communication and interaction, accompanied by restricted, repetitive behaviors and interests.

autocrine

Referring to a signal that is secreted by a cell into its environment and that feeds back to the same cell.

autoimmune disorder

A disorder caused when the immune system mistakenly attacks a person’s own body, thereby interfering with normal functioning.

autonomic ganglia

Collections of nerve cell bodies, belonging to the autonomic division of the peripheral nervous system, that are found in various locations and innervate the major organs.

autonomic nervous system

The part of the peripheral nervous system that supplies neural connections to glands and to smooth muscles of internal organs.

autoradiography

A histological technique that shows the distribution of radioactive chemicals in tissues.

autoreceptor

A receptor for a synaptic transmitter that is located in the presynaptic membrane, telling the axon terminal how much transmitter has been released.

AVP

See arginine vasopressin.

axo-axonic

Referring to a synapse in which a presynaptic axon terminal synapses onto another axon’s terminal.

axo-dendritic

Referring to a synapse in which a presynaptic axon terminal synapses onto a dendrite of the postsynaptic neuron, either via a dendritic spine or directly onto the dendrite itself.

axon

A single extension from the nerve cell that carries action potentials from the cell body to other neurons.

axon collateral

A branch of an axon from a single neuron.

axon hillock

A cone-shaped area from which the axon originates out of the cell body; functionally, the integration zone of the neuron.

axon terminal

Also called synaptic bouton. The end of an axon or axon collateral, which forms a synapse on a neuron or other target cell.

axonal transport

The transportation of materials from the neuronal cell body to distant regions in the dendrites and axons, and from the axon terminals back to the cell body.

axo-somatic

Referring to a synapse in which a presynaptic axon terminal synapses onto the cell body (soma) of the postsynaptic neuron.

B cell or B lymphocyte

An immune system cell, formed in the bone marrow (hence the B), that mediates humoral immunity.

Bá lint’s syndrome

Three co-occurring symptoms— simultagnosia, oculomotor apraxia, and optic ataxia— that may occur after bilateral lesions of cortical attentional systems.

ballistic movement

A rapid muscular movement that is generally preprogrammed.

bar detector

See simple cortical cell.

barbiturate

A powerful sedative anxiolytic derived from barbituric acid, with dangerous addiction and overdose potential.

bariatric

Having to do with treatment of obesity.

baroreceptor

A pressure receptor in the heart or a major artery that detects a fall in blood pressure.

basal dendrite

One of several dendrites on a pyramidal cell that extend horizontally from the cell body.

basal forebrain

A ventral region in the forebrain that has been implicated in consciousness and sleep.

basal ganglia

A group of forebrain nuclei, including caudate nucleus, globus pallidus, and putamen, found deep within the cerebral hemispheres.

basal metabolism

The consumption of energy by the basic life-sustaining functions of the body.

basilar artery

An artery, formed by the fusion of the vertebral arteries, that supplies blood to the brainstem and to the posterior cerebral arteries.

basilar membrane

A membrane in the cochlea that contains the principal structures involved in auditory transduction.

bass

An aspect of pitch corresponding to the subjective experience of low-frequency sounds (especially musical sounds like those from a bass guitar).

batrachotoxin

A toxin, secreted by poison arrow frogs, that selectively interferes with Na⁺ channels.

Bcl-2

A family of proteins that regulate apoptosis.

BDNF

See brain-derived neurotrophic factor.

behavioral intervention

An approach to finding relations between body variables and behavioral variables that involves intervening in the behavior of an organism and looking for resultant changes in body structure or function.

behavioral medicine

See health psychology.

behavioral neuroscience

Also called biological psychology. The study of the neural bases of behavior and mental processes.

behavioral teratology

The study of impairments in behavior that are produced by embryonic or fetal exposure to toxic substances.

Bell’s palsy

A disorder, usually caused by viral infection, in which the facial nerve on one side stops conducting action potentials, resulting in paralysis on one side of the face.

benzodiazepine agonists

A class of antianxiety drugs that bind to sites on GABA_A receptors.

benzodiazepines

A class of antianxiety drugs that bind with high affinity to receptor molecules in the central nervous system. One example is diazepam (Valium).

β-amyloid

A protein that accumulates in senile plaques in Alzheimer’s disease.

β-secretase

An enzyme that cleaves amyloid precursor protein, forming β-amyloid, which can lead to Alzheimer’s disease.

binaural

Referring to two ears.

binding affinity

Also called simply affinity. The propensity of molecules of a drug (or other ligand) to bind to receptors.

binding problem

The question of how the brain understands which individual attributes blend together into a single object, when these different features are processed by different regions in the brain.

binge eating

The paroxysmal intake of large quantities of food, often of poor nutritional value and high in calories.

binocular deprivation

Depriving both eyes of form vision, as by sealing the eyelids.

bioavailable

Referring to a substance, usually a drug, that is present in the body in a form that is able to interact with physiological mechanisms.

biological psychology

See behavioral neuroscience.

biotransformation

The process in which enzymes convert a drug into a metabolite that is itself active, possibly in ways that are substantially different from the actions of the original substance.

bipolar cells

A class of interneurons of the retina that receive information from rods and cones and pass the information to retinal ganglion cells.

bipolar disorder

Formerly called manic-depressive illness. A psychiatric disorder characterized by periods of depression that alternate with excessive, expansive moods.

bipolar neuron

A nerve cell that has a single dendrite at one end and a single axon at the other end.

blind spot

The portion of the visual field from which light falls on the optic disc. Because there are no receptors in this region, light striking it cannot be seen.

blood-brain barrier

The mechanisms that make the movement of substances from blood vessels into brain cells more difficult than exchanges in other body organs, thus affording the brain greater protection from exposure to some substances found in the blood.

blotting

Transferring DNA, RNA, or protein fragments to nitrocellulose following separation via gel electrophoresis. The blotted substance can then be labeled.

border cell

A neuron that selectively fires when an animal arrives at the perimeter of a local spatial cognitive map.

bottom-up attention

See reflexive attention.

bottom-up process

A process in which lower-order mechanisms, like sensory inputs, trigger additional processing by higher-order systems. There may be no conscious awareness until late in the process.

botulinum toxin

A toxin that cleaves SNAREs (Soluble NSF Attachment Protein REceptors), such as t-SNAREs and v-SNAREs, disabling neurotransmitter release.

bovine spongiform encephalopathy (BSE)

Also called mad cow disease. A disorder caused by improperly formed prion proteins, leading to dementia and death.

brain self-stimulation

The process in which animals will work to provide electrical stimulation to particular brain sites, presumably because the experience is very rewarding.

brain-derived neurotrophic factor (BDNF)

A protein purified from the brains of animals that can keep some classes of neurons alive.

brainstem

The region of the brain that consists of the midbrain, the pons, and the medulla.

Broca’s aphasia

See nonfluent aphasia.

Broca’s area

A region of the frontal lobe of the brain that is involved in the production of speech.

BSE

See bovine spongiform encephalopathy.

bulimia

Also called bulimia nervosa. A syndrome in which individuals periodically gorge themselves, usually with “ junk food,” and then either vomit or take laxatives to avoid weight gain.

bungarotoxin

A neurotoxin from the venom of the banded krait that selectively blocks acetylcholine receptors.

C fiber

A small, unmyelinated axon that conducts pain information slowly and adapts slowly.

Ca²⁺

See calcium ion.

caffeine

A stimulant compound found in coffee, cacao, and other plants.

CAH

See congenital adrenal hyperplasia.

calcium ion (Ca²⁺)

A calcium atom that carries a double positive charge because it has lost two electrons.

CAM

See cell adhesion molecule.

cAMP

See cyclic adenosine monophosphate.

Cannon-Bard theory

The theory that our experience of emotion is independent of the simultaneous physiological changes that accompany it.

capsaicin

A compound synthesized by various plants to deter predators by mimicking the experience of burning.

carotid arteries

The major arteries that ascend the left and right sides of the neck to the brain, supplying blood to the anterior and middle cerebral arteries.

Cas9

CRISPR associated enzyme 9. A bacterial enzyme that induces a break in double-stranded DNA as part of the CRISPR system.

caspases

A family of proteins that regulate cell death (apoptosis).

castration

Removal of the gonads, usually the testes.

CAT or CT

See computerized axial tomography.

cataplexy

Sudden loss of muscle tone, leading to collapse of the body without loss of consciousness.

catecholamines

A class of monoamines that serve as neurotransmitters, including dopamine and norepinephrine.

cation

A positively charged ion, such as a potassium or sodium ion.

caudal

See posterior.

caudate nucleus

One of the basal ganglia. It has a long extension or tail.

CBT

See cognitive behavioral therapy.

CCK

See cholecystokinin.

cell adhesion molecule (CAM)

A protein found on the surface of a cell that guides cell migration and/or axonal pathfinding.

cell assembly

A large group of cells that tend to be active at the same time because they have been activated simultaneously or in close succession in the past.

cell body

Also called soma. The region of a neuron that is defined by the presence of the cell nucleus.

cell death

Also called apoptosis. The developmental process during which “ surplus” cells die.

cell differentiation

The developmental stage in which cells acquire distinctive characteristics, such as those of neurons, as the result of expressing particular genes.

cell membrane

The lipid bilayer that ensheathes a cell.

cell migration

The movement of cells from site of origin to final location.

cell nucleus

The spherical central structure of a cell that contains the chromosomes.

cell-autonomous

Referring to cell processes that are directed by the cell itself rather than being under the influence of other cells.

cell-cell interactions

The general process during development in which one cell affects the differentiation of other, usually neighboring, cells.

central deafness

A hearing impairment that is related to lesions in auditory pathways or centers, including sites in the brainstem, thalamus, or cortex.

central nervous system (CNS)

The portion of the nervous system that includes the brain and the spinal cord.

central pattern generator

Neural circuitry that is responsible for generating the rhythmic pattern of a behavior such as walking.

central sulcus

A fissure that divides the frontal lobe from the parietal lobe.

cerebellum

A structure located at the back of the brain, dorsal to the pons, that is involved in the central regulation of movement.

cerebral cortex

Also called simply cortex. The outer covering of the cerebral hemispheres that consists largely of neuronal cell bodies and their branches.

cerebral hemispheres

The right and left halves of the forebrain.

cerebral lateralization

Specialization of one cerebral hemisphere for a particular intellectual function.

cerebrocerebellum

The lowermost part of the cerebellum, consisting especially of the lateral part of each cerebellar hemisphere.

cerebrospinal fluid (CSF)

The fluid that fills the cerebral ventricles.

cervical

Referring to the topmost eight segments of the spinal cord, in the neck region.

cGMP

See cyclic guanosine monophosphate.

channelopathy

A genetic abnormality of ion channels, causing a variety of symptoms.

channelrhodopsin

A protein that, in response to light of the proper wavelength, opens a channel to admit sodium ions, which results in excitation of the neuron.

ChAT

See choline acetyltransferase.

chemical transmitter

See neurotransmitter.

chemically gated ion channel

See ligand-gated ion channel.

chemoaffinity hypothesis

The notion that each cell has a chemical identity that directs it to synapse on the proper target cell during development.

chemoattractants

Compounds that attract particular classes of axonal growth cones.

chemorepellents

Compounds that repel particular classes of axonal growth cones.

chlorpromazine

An antipsychotic drug, one of the class of phenothiazines.

cholecystokinin (CCK)

A peptide hormone, released by the gut after ingestion of food high in protein and/or fat, that also serves as a signaling molecule in the brain.

choline acetyltransferase (Chat)

An important enzyme involved in the synthesis of the neurotransmitter acetylcholine.

cholinergic

Referring to cells that use acetylcholine as their synaptic transmitter.

choroid plexus

A highly vascular portion of the lining of the ventricles that secretes cerebrospinal fluid.

chromosome

A complex of condensed strands of DNA and associated protein molecules, found in the nucleus of cells.

chronic traumatic encephalopathy (CTE)

Also called dementia pugilistica or punch-drunk. The dementia that develops in boxers or other athletes who are subjected to repeated blows to the head.

ciliary muscle

One of the muscles that controls the shape of the lens inside the eye, focusing an image on the retina.

cilium

A hairlike cellular extension.

cingulate cortex

Also called cingulum. A region of medial cerebral cortex that lies dorsal to the corpus callosum.

cingulate gyrus

A cortical portion of the limbic system, found in the frontal and parietal midline.

cingulum

See cingulate cortex.

circadian rhythm

A pattern of behavioral, biochemical, or physiological fluctuation that has a 24-hour period.

circannual

Occurring on a roughly annual basis.

circle of Willis

A vascular structure at the base of the brain that is formed by the joining of the carotid and basilar arteries.

circumvallate papillae

One of three types of small structures on the tongue that contain taste receptors, located in the back of the tongue.

circumventricular organ

An organ that lies in the wall of a cerebral ventricle and monitors the composition of body fluids.

CJD

See Creutzfeldt-Jakob disease.

Cl–

See chloride ion.

classical conditioning

Also called Pavlovian conditioning. A type of associative learning in which an originally neutral (conditioned) stimulus acquires the power to elicit the response normally elicited by another (unconditioned) stimulus after the two stimuli are paired. A response elicited by the unconditioned stimulus (US) is called an unconditioned response (UR); a response elicited by the conditioned stimulus (CS) alone is called a conditioned response (CR).

claustrum

A thin sheet of neurons, situated within the white matter lateral to the basal ganglia, that has been implicated in conscious awareness.

cloacal exstrophy

A rare medical condition in which XY individuals are born completely lacking a penis.

clone

1. An asexually produced organism that is genetically identical to the organism it was grown from.

closed-loop control mechanism

A control mechanism that provides a flow of information from whatever is being controlled to the device that controls it.

clozapine

An atypical antipsychotic.

CMR1

See cool-menthol receptor 1.

CNS

See central nervous system.

cocaine

A drug of abuse, derived from the coca plant, that acts by potentiating catecholamine stimulation.

coccygeal

Referring to the lowest spinal vertebra (also called the tailbone).

cochlea

A snail-shaped structure in the inner ear that contains the primary receptor cells for hearing.

cochlear implant

An electromechanical device that detects sounds and selectively stimulates nerves in different regions of the cochlea via surgically implanted electrodes.

cochlear nuclei

Brainstem nuclei that receive input from auditory hair cells and send output to the superior olivary complex.

cocktail party effect

The selective enhancement of attention in order to filter out distracters, such as while listening to one person talking in the midst of a noisy party.

coding

The rules by which action potentials in a sensory system reflect a physical stimulus.

codon

A set of three nucleotides that uniquely encodes one particular amino acid.

cognitive attribution model

The theory that our emotional experience results from cognitive analysis of the context around us, such that physiological changes may accentuate emotions but not specify which emotion we experience.

cognitive behavioral therapy (CBT)

Psychotherapy aimed at correcting negative thinking and improving interpersonal relationships.

cognitive map

A mental representation of a spatial relationship.

cognitively impenetrable

Referring to data-processing operations of the central nervous system that are unconscious.

coincidence detector

A device that senses the co-occurrence of two events.

coitus

See copulation.

co-localization

Also called co-release. In neurons, the appearance of more than one neurotransmitter in a given presynaptic terminal.

communication

Information transfer between two individuals.

comorbid

Referring to the tendency of certain diseases or disorders to occur together in individuals.

competitive ligand

A substance that directly competes with the endogenous ligand for the same binding site on a receptor molecule.

complex cortical cell

A cell in the visual cortex that responds best to a bar of a particular size and orientation anywhere within a particular area of the visual field.

complex environment

See enriched condition.

complex partial seizure

In epilepsy, a type of seizure that doesn’t involve the entire brain and therefore can cause a wide variety of symptoms.

computerized axial tomography (CAT or CT)

A noninvasive technique for examining brain structure in humans through computer analysis of X-ray absorption at several positions around the head.

concentration gradient

Variation of the concentration of a substance within a region.

concordant

Referring to any trait that is seen in both individuals of a pair of twins.

concussion

Also called minor traumatic brain injury (mTBI). An injury resulting from a blow to the head and associated with temporary neurological symptoms such as memory loss or other cognitive impairments, pain, and visual disturbances.

conditional knockout

A gene that can be selectively deactivated in specific tissues and/or at a specific stage of development.

conduction aphasia

An impairment in the repetition of words and sentences.

conduction deafness

A hearing impairment that is associated with pathology of the external-ear or middle-ear cavities.

conduction velocity

The speed at which an action potential is propagated along the length of an axon (or section of peripheral nerve).

conduction zone

The part of the neuron over which the nerve’s electrical signal may be actively propagated. It usually corresponds to the cell’s axon.

cones

A class of photoreceptor cells in the retina that are responsible for color vision.

confabulate

To fill in a gap in memory with a falsification. It often occurs in Korsakoff’s syndrome.

congenital adrenal hyperplasia (CAH)

Any of several genetic mutations that can result in exposure of a female fetus to adrenal androgens, which results in a clitoris that is larger than normal at birth.

congenital hypothyroidism

See cretinism.

congenital insensitivity to pain

The condition of being born without the ability to perceive pain.

conjunction search

A search for an item that is based on two or more features (e.g., size and color) that together distinguish the target from distracters that may share some of the same attributes.

connectionist model of aphasia

The theory proposing that Wernicke’s area and Broca’s area, connected by the arcuate fasciculus, specialize in the receptive and expressive aspects of language, respectively.

connexon

A protein assembly that provides an open ion channel between two neurons, forming an electrical synapse between them.

consciousness

The state of awareness of one’s own existence and experience.

consciously controlled attention

See voluntary attention.

conserved

In the context of evolution, referring to a trait that is passed on from a common ancestor to two or more descendant species.

consolidation

A stage of memory formation in which information in short-term or intermediate-term memory is transferred to long-term memory.

constraint-induced movement therapy (CIMT)

A therapy for recovery of limb movement after stroke or injury, in which the unaffected limb is constrained while the person is required to perform tasks with the affected contralateral limb.

contralateral

In anatomy, pertaining to a location on the opposite side of the body. Compare ipsilateral.

convergence

The phenomenon of neural connections in which many cells send signals to a single cell.

convergent evolution

The evolutionary process by which responses to similar ecological features bring about similarities in behavior or structure among animals that are only distantly related (i.e., that differ in genetic heritage).

Coolidge effect

The propensity of an animal that has appeared sexually satiated with a present partner to resume sexual activity when provided with a novel partner.

cool-menthol receptor 1 (CMR1)

Also called TRPM8. A sensory receptor, found in some free nerve endings, that opens an ion channel in response to a mild temperature drop or exposure to menthol.

copulation

Also called coitus. The sexual act.

copulatory lock

Reproductive behavior in which the male’s penis swells after ejaculation so that the male and female are forced to remain joined for 5– 15 minutes. It occurs in dogs and some rodents, but not in humans.

co-release

See co-localization.

cornea

The transparent outer layer of the eye, whose curvature is fixed. It bends light rays and is primarily responsible for forming the image on the retina.

coronal plane

Also called frontal plane or transverse plane. The plane that divides the body or brain into front and back parts. Compare horizontal plane and sagittal plane.

corpora lutea

The structures formed from collapsed ovarian follicles subsequent to ovulation. The corpora lutea are a major source of progesterone.

corpus callosum

The main band of axons that connects the two cerebral hemispheres.

correlation

The covariation of two measures.

cortical column

One of the vertical columns that constitute the basic organization of the neocortex.

cortical deafness

A hearing impairment that is caused by a fault or defect in the cortex.

corticospinal system

See pyramidal system.

cortisol

A glucocorticoid stress hormone of the adrenal cortex.

cranial nerve

A nerve that is connected directly to the brain.

CREB

cAMP responsive element– binding protein. A protein that binds the promoter region of several genes involved in neural plasticity when activated by cyclic AMP (cAMP).

Cre-recombinase

A bacterial enzyme normally made by bacteria that recognizes loxP, which is a specific sequence of nucleotides, removes a segment of DNA flanked by two loxP sites, and then recombines the DNA at those loxP sites.

cretinism

Also called congenital hypothyroidism. Reduced stature and intellectual disability caused by thyroid deficiency during early development.

Creutzfeldt-Jakob disease (CJD)

A brain disorder in humans, leading to dementia and death, that is caused by improperly folded prion proteins; the human equivalent of mad cow disease.

crib death

See sudden infant death syndrome.

CRISPR

clustered regularly interspaced short palindromic repeats. A system of gene manipulation that evolved in single-celled organisms and is exploited by scientists for gene editing.

cross-tolerance

A condition in which the development of tolerance for one drug causes an individual to develop tolerance for another drug.

crystallization

The final stage of birdsong formation, in which fully formed adult song is achieved.

CSF

See cerebrospinal fluid.

CT or CAT

See computerized axial tomography.

CTE

See chronic traumatic encephalopathy.

cue-induced drug use

An increased likelihood to use a drug (especially an addictive drug) because of the presence of environmental stimuli that were present during previous use of the same drug.

cupula

A small gelatinous structure, containing hair cells that detect fluid movement within the semicircular canals of the the vestibular system.

curare

An alkaloid neurotoxin that causes paralysis by blocking acetylcholine receptors in muscle.

Cushing’s syndrome

A condition in which levels of adrenal glucocorticoids are abnormally high.

cyclic adenosine monophosphate (cyclic AMP, or cAMP)

A second messenger activated in many target cells in response to synaptic or hormonal stimulation.

cyclic guanosine monophosphate (cyclic GMP, or cGMP)

A second messenger activated in some target cells in response to synaptic or hormonal stimulation.

cytokine

A protein that induces the proliferation of other cells, as in the immune system.

cytoplasm

See intracellular fluid.

DA

See dopamine.

dB

See decibel.

DBS

See deep brain stimulation.

deafness

Hearing loss so profound that speech perception is lost.

death gene

A gene that is expressed only when a cell becomes committed to natural cell death (apoptosis).

decibel (dB)

A measure of sound intensity.

declarative memory

A memory that can be stated or described.

decomposition of movement

Difficulty of movement in which gestures are broken up into individual segments instead of being executed smoothly. It is a symptom of cerebellar lesions.

decorticate rage

Also called sham rage. Sudden intense rage characterized by actions (such as snarling and biting in dogs) that lack clear direction.

deep brain stimulation (DBS)

Mild electrical stimulation through an electrode that is surgically implanted deep in the brain.

deep dyslexia

Acquired dyslexia in which the person reads a word as another word that is semantically related.

default mode network

The regions of the brain that are active when the brain is awake and at rest and attention is not being directed to external events.

degradation

The chemical breakdown of a neurotransmitter into inactive metabolites.

delayed non-matching-to-sample task

A test in which, on each trial, the participant must select the stimulus not seen previously.

δ9-tetrahydrocannabinol (THC)

The major active ingredient in marijuana.

delta wave

The slowest type of EEG wave, about 1 Hz, characteristic of stage 3 sleep.

delusion

A false belief strongly held in spite of contrary evidence.

dementia

Drastic failure of cognitive ability, including memory failure and loss of orientation.

dementia pugilistica

See chronic traumatic encephalopathy.

dendrite

One of the extensions of the cell body that are the receptive surfaces of the neuron.

dendritic knob

A portion of an olfactory receptor cell present in the olfactory epithelium.

dendro-dendritic

Referring to a synapse in which a synaptic connection forms between the dendrites of two neurons.

dentate gyrus

A strip of gray matter in the hippocampal formation.

deoxyribonucleic acid (DNA)

A nucleic acid that is present in the chromosomes of cells and encodes hereditary information.

dependence

Also called addiction. In the context of drugs, the strong desire to self-administer a drug of abuse.

dependent variable

The factor that an experimenter measures to monitor a change in response to manipulation of an independent variable.

depolarization

A reduction in membrane potential (the interior of the neuron becomes less negative).

depressants

A class of drugs that act to reduce neural activity.

depression

A psychiatric condition characterized by such symptoms as an unhappy mood; loss of interests, energy, and appetite; and difficulty concentrating.

dermatome

A strip of skin innervated by a particular spinal nerve.

dermis

The middle layer of skin, between the epidermis and the hypodermis.

designer receptors exclusively activated by designer drugs (DREADDs)

Engineered G protein receptors made to respond only to synthetic ligands so that scientists can selectively activate neurons made to express those receptors.

desynchronized EEG

Also called beta activity. EEG activity seen in wakefulness, comprising a mix of many different high frequencies with low amplitude.

dexamethasone suppression test

A test of pituitary-adrenal function in which the participant is given dexamethasone, a synthetic glucocorticoid hormone, which should cause a decline in the production of adrenal corticosteroids.

dfMRI

See dyadic functional MRI.

DHT

See dihydrotestosterone.

diabetes mellitus

Excessive glucose in the urine, caused by the failure of insulin to induce glucose absorption by the body.

Diablo

A protein released by mitochondria, in response to high calcium levels, that activates apoptosis.

dichotic presentation

The simultaneous delivery of different stimuli to the right and the left ears.

diencephalon

The posterior part of the forebrain, including the thalamus and hypothalamus.

diffusion

The spontaneous spread of molecules of one substance among molecules of another substance until a uniform concentration is achieved.

diffusion tensor imaging (DTI)

A modified form of MRI in which the diffusion of water in a confined space is exploited to produce images of axonal fiber tracts.

digestion

The process by which food is broken down to provide energy and nutrients.

dihydrotestosterone (DHT)

The 5α-reduced metabolite of testosterone; a potent androgen that is principally responsible for the masculinization of the external genitalia in mammalian sexual differentiation.

dimer

A complex of two proteins that have bound together.

discordant

Referring to any trait that is seen in only one individual of a pair of twins.

dishabituation

The restoration of response amplitude following habituation.

dissociative drug

A type of drug that produces a dreamlike state in which consciousness is partly separated from sensory inputs.

dissociative thinking

A condition, seen in schizophrenia, that is characterized by disturbances of thought and difficulty relating events properly.

distal

In anatomy, toward the periphery of an organism or the end of a limb. Compare proximal.

diurnal

Active during the light periods of the daily cycle.

divergence

The phenomenon of neural connections in which one cell sends signals to many other cells.

divided-attention task

A task in which the participant is asked to simultaneously focus attention on two or more stimuli.

dizygotic

Referring to twins derived from separate eggs (fraternal twins). Such twins are no more closely related genetically than are other full siblings.

DNA

See deoxyribonucleic acid.

DNA sequencing

The process by which the order of nucleotides in a gene, or amino acids in a protein, is determined.

dopamine (DA)

A monoamine transmitter found in the midbrain— especially the substantia nigra— and basal forebrain.

dopamine hypothesis

The hypothesis that schizophrenia results from either excessive levels of synaptic dopamine or excessive postsynaptic sensitivity to dopamine.

dorsal

In anatomy, toward the back of the body or the top of the brain. Compare ventral.

dorsal column nuclei

Collection of neurons in the medulla that receive somatosensory information via the dorsal columns of the spinal cord. These neurons send their axons across the midline and to the thalamus.

dorsal column system

A somatosensory system that delivers most touch stimuli via the dorsal columns of spinal white matter to the brain.

dorsal root

The branch of a spinal nerve, entering the dorsal horn of the spinal cord, that carries sensory information from the peripheral nervous system to the spinal cord.

dose-response curve (DRC)

A formal plot of a drug’s effects (on the y-axis) versus the dose given (on the x-axis).

Down syndrome

A syndrome caused by inheriting an extra copy of chromosome 21, usually accompanied by intellectual disability.

down-regulation

A compensatory reduction in receptor availability at the synapses of a neuron.

DRC

See dose-response curve.

DREADDs

See designer receptors exclusively activated by designer drugs.

DTI

See diffusion tensor imaging.

DTI tractography

Also called fiber tracking. Visualization of the orientation and terminations of white matter tracts in the living brain via diffusion tensor imaging.

dual dependence

Dependence for emergent drug effects that occur only when two drugs are taken simultaneously.

dualism

Within the concept of separation of soul and body, the notion promoted by René Descartes that the mind is subject only to spiritual interactions while the body is subject only to material interactions.

duplex theory

A theory that we localize sound by combining information about intensity differences and latency differences between the two ears.

dura mater

The outermost of the three meninges that surround the brain and spinal cord.

dyadic functional MRI (dfMRI)

An fMRI technique in which the brains of two interacting individuals are simultaneously imaged.

dynorphins

One of three kinds of endogenous opioids, substances that reduce pain perception.

dyskinesia

Difficulty or distortion in voluntary movement.

dyslexia

A reading disorder attributed to brain impairment.

dysphoria

Unpleasant feelings; the opposite of euphoria.

dystrophin

A protein that is needed for normal muscle function.

ear canal

A tube leading from the pinna to the middle ear.

eardrum

See tympanic membrane.

early-selection model

A model of attention in which the attentional bottleneck filters out stimuli before even preliminary perceptual analysis has occurred.

easy problem of consciousness

The problem of how to read current conscious experiences directly from people’s brains as they’re happening.

EC

See enriched condition.

ecological niche

The unique assortment of environmental opportunities and challenges to which each organism is adapted.

Ecstasy

See MDMA.

ectoderm

The outer cellular layer of the developing embryo, giving rise to the skin and the nervous system.

ectopia

Something out of place— for example, clusters of neurons seen in unusual positions in the cortex of someone suffering from dyslexia.

ectopic transmission

Cell-cell communication based on release of neurotransmitter in regions outside traditional synapses.

ectotherm

An animal whose body temperature is regulated by, and whose heat comes mainly from, the environment. Examples include snakes and bees.

edema

The swelling of tissue, such as in the brain, in response to injury.

edge detector

See simple cortical cell.

EEG

See electroencephalogram and electroencephalography.

efferent

In reference to axons, carrying information from the central nervous system to the periphery. Compare afferent.

efficacy

Also called intrinsic activity. The extent to which a drug activates a response when it binds to a receptor.

ejaculation

The forceful expulsion of semen from the penis.

electrical synapse

Also called gap junction. The region between neurons where the membranes are so close that changes in potential can flow from one to the other without being translated into a chemical message.

electroencephalogram (EEG)

A recording of gross electrical activity of the brain recorded from electrodes placed on the scalp.

electroencephalography (EEG)

The recording and study of gross electrical activity of the brain recorded from electrodes placed on the scalp.

electroconvulsive therapy (ECT)

Also called shock therapy. A last-resort treatment for intractable depression, in which a strong electrical current is passed through the brain, causing a seizure.

electromyography (EMG)

The electrical recording of muscle activity.

electro-oculography (EOG)

The electrical recording of eye movements.

electrostatic pressure

The propensity of charged molecules or ions to move toward areas with the opposite charge.

embryo

The earliest stage in a developing animal.

embryonic stem cell

A cell, derived from an embryo, that has the capacity to form any type of tissue that a donor might produce.

EMG

See electromyography.

emotion

A subjective mental state that is usually accompanied by distinctive behaviors, feelings, and involuntary physiological changes.

emotional dyscontrol syndrome

A condition consisting of temporal lobe disorders that may underlie some forms of human violence.

encephalization factor

A measure of brain size relative to body size.

encoding

In memory formation, the stage in which the information entering sensory channels is passed into short-term memory.

endocannabinoid

An endogenous ligand of cannabinoid receptors, thus an analog of marijuana that is produced by the brain.

endocast

A cast of the cranial cavity of a skull, especially useful for studying fossils of extinct species.

endocrine

Referring to glands that release chemicals to the interior of the body. These glands secrete the principal hormones.

endocrine gland

A gland that secretes hormones into the bloodstream to act on distant targets.

endogenous

Produced inside the body.

endogenous ligand

Any substance that is produced within the body and selectively binds to the type of receptor that is under study.

endogenous opioids

A family of peptide transmitters that have been called the body’s own narcotics. The three kinds are enkephalins, endorphins, and dynorphins.

endogenously controlled attention

See voluntary attention.

endophenotype

Behavioral or physical characteristics accompanying susceptibility to a particular disorder, which may be used to identify those at risk.

endorphins

One of three kinds of endogenous opioids, substances that reduce pain perception.

endotherm

An animal whose body temperature is regulated chiefly by internal metabolic processes. Examples include mammals and birds.

engram

The physical basis of a memory in the brain. Sometimes referred to as a memory trace on the assumption that it involves changes in a neural circuit rather than a single neuron.

enkephalins

One of three kinds of endogenous opioids, substances that reduce pain perception.

enriched condition (EC)

Also called complex environment. A condition in which laboratory rodents are group-housed with a wide variety of stimulus objects.

enteric nervous system

An extensive mesh-like system of neurons that governs the functioning of the gut.

enterotype

Each individual’s personal composition of gut microbiota.

entrainment

The process of synchronizing a biological rhythm to an environmental stimulus.

enzyme

A complicated protein whose action increases the probability of a specific chemical reaction.

EOG

See electro-oculography.

ependymal layer

See ventricular zone.

epidemiology

The statistical study of patterns of disease in a population.

epidermis

The outermost layer of skin, over the dermis.

epigenetic regulation

Process affecting the expression of a particular gene or genes without affecting the sequence of nucleotides making up the gene itself.

epigenetic transmission

The passage of epigenetic modifications of a gene from one generation to another.

epigenetics

The study of factors that affect gene expression without making any changes in the nucleotide sequence of the genes themselves.

epilepsy

A brain disorder marked by major sudden changes in the electrophysiological state of the brain that are referred to as seizures.

epinephrine

Also called adrenaline. A compound that acts both as a hormone (secreted by the adrenal medulla under the control of the sympathetic nervous system, which prepares the body for action) and as a synaptic transmitter.

episodic memory

Memory of a particular incident or a particular time and place.

EPSP

See excitatory postsynaptic potential.

equilibrium

In a neuron, the state in which the number of ions crossing the cell membrane in one direction is matched by the number crossing in the opposite direction.

equilibrium potential

The voltage across a permeable membrane that exactly counteracts the movement of ions from the side with a high concentration to the side with a low concentration.

ERP

See event-related potential.

estradiol

See 17 β-estradiol.

estrogens

A class of steroid hormones produced by female gonads.

estrus

The period during which female animals are sexually receptive.

eukaryote

Any organism whose cells have the genetic material contained within a nuclear envelope.

event-related potential (ERP)

Also called evoked potential. Averaged EEG recordings measuring brain responses to repeated presentations of a stimulus.

evoked potential

See event-related potential.

evolution

In biology, the process by which a population of interbreeding individuals changes over long periods of time.

evolution by natural selection

The Darwinian theory that evolution proceeds by differential success in reproduction.

evolutionary psychology

A field devoted to asking how natural selection has shaped behavior in humans and other animals.

excitatory postsynaptic potential (EPSP)

A depolarizing potential in the postsynaptic neuron that is caused by excitatory connections. EPSPs increase the probability that the postsynaptic neuron will fire an action potential.

excitotoxicity

The property by which neurons die when overstimulated, as with large amounts of glutamate.

executive function

A neural and cognitive system that helps develop plans of action and organizes the activities of other high-level processing systems.

exocrine gland

A gland whose secretions exit the body via ducts.

exocytosis

In neurons, the process by which a synaptic vesicle fuses with the presynaptic terminal membrane to release neurotransmitter into the synaptic cleft.

exogenous

Arising from outside the body.

exogenous ligand

Any substance that originates outside the body and selectively binds to the type of receptor that is under study.

exogenously controlled attention

See reflexive attention.

expression

The process by which a cell makes an mRNA transcript of a particular gene.

external ear

The part of the ear that we readily see (the pinna) and the canal that leads to the eardrum.

external fertilization

The process by which eggs are fertilized outside of the female’s body, as in many fishes and amphibians.

extinction

Also called extinction of simultaneous double stimulation. In the context of neurology, an inability to recognize the double nature of stimuli presented simultaneously to both sides of the body. People experiencing extinction report the stimulus from only one side.

extracellular compartment

The fluid space of the body that exists outside the cells.

extracellular fluid

The fluid in the spaces between cells (interstitial fluid) and in the vascular system.

extrafusal fiber

One of the ordinary muscle fibers that lie outside the spindles and provide most of the force for muscle contraction.

extraocular muscle

One of the muscles attached to the eyeball that control its position and movements.

extrapyramidal system

A motor system that includes the basal ganglia and some closely related brainstem structures.

extrastriate cortex

Visual cortex outside of the primary visual (striate) cortex.

FA

See fractional anisotropy.

face blindness

See prosopagnosia.

facial feedback hypothesis

The hypothesis that our emotional experience is affected by the sensory feedback we receive during particular facial expressions, such as smiling.

facial nerve

Cranial nerve VII, which receives information from the face and controls the superficial muscles there.

FAS

See fetal alcohol syndrome.

fast-twitch muscle fiber

A type of striated muscle that contracts rapidly but fatigues readily.

fatal familial insomnia

An inherited disorder in which humans sleep normally at the beginning of their life but stop sleeping in midlife and die 7– 24 months later.

fear conditioning

A type of classical conditioning where a previously neutral stimulus is repeatedly paired with shock or some other unpleasant experience, causing the individual to act fearful in response to the stimulus.

feature integration theory

The idea that conjunction searches involve multiple cognitive feature maps— overlapping representations of the search array based on individual stimulus attributes.

feature search

A search for an item in which the target pops out right away because it possesses a unique attribute.

fecal transplantation

A medical procedure in which gut microbiota, via fecal matter, are transferred from a donor to a host.

FEF

See frontal eye field.

fetal alcohol syndrome (FAS)

A disorder, including intellectual disability and characteristic facial anomalies, that affects children exposed to too much alcohol (through maternal ingestion) during fetal development.

fetus

A developing individual after the embryo stage.

fiber tracking

See DTI tractography.

filopodia

Very fine, tubular outgrowths from the growth cone of an axon or dendrite.

final common pathway

The information-processing pathway consisting of all the motor neurons in the body. Motor neurons are known by this collective term because they receive and integrate all motor signals from the brain and then direct movement accordingly.

flaccid paralysis

A loss of reflexes below the level of transection of the spinal cord.

flower spray ending

See secondary sensory ending.

fluent aphasia

Also called Wernicke’s aphasia. A language impairment characterized by fluent, meaningless speech and little language comprehension. It is related to damage in Wernicke’s area.

fMRI

See functional MRI.

foliate papillae

One of three types of small structures on the tongue that contain taste receptors, located along the sides of the tongue.

follicles

Ovarian structures containing immature ova.

follicle-stimulating hormone (FSH)

A gonadotropin, named for its actions on ovarian follicles.

forebrain

Also called prosencephalon. The anterior division of the brain, containing the cerebral hemispheres, the thalamus, and the hypothalamus.

fornix

A fiber tract that extends from the hippocampus to the mammillary body.

Fourier analysis

The mathematical decomposition of a complex pattern into a sum of sine waves.

fourth ventricle

The passageway within the pons that receives cerebrospinal fluid from the third ventricle and releases it to surround the brain and spinal cord.

fovea

The central portion of the retina, packed with the most photoreceptors and therefore the center of our gaze.

fractional anisotropy (FA)

The tendency of water to diffuse more readily along the long axis of an enclosed space, such as an axon. It is the basis of diffusion tensor imaging.

fragile X syndrome

A condition that is a frequent cause of inherited intellectual disability. It is produced by a fragile site on the X chromosome that seems prone to breaking because the DNA there is unstable.

free nerve ending

An axon that terminates in the skin without any specialized cell associated with it and that detects pain and/or changes in temperature.

free-running

Referring to a rhythm of behavior shown by an animal deprived of external cues about time of day.

frequency

The number of cycles per second in a sound wave, measured in hertz (Hz).

frontal eye field (FEF)

An area in the frontal lobe of the brain containing neurons important for establishing gaze in accordance with cognitive goals (top-down processes) rather than with any characteristics of stimuli (bottom-up processes).

frontal lobe

The most anterior portion of the cerebral cortex.

frontal plane

See coronal plane.

FSH

See follicle-stimulating hormone.

functional MRI (fMRI)

Magnetic resonance imaging that detects changes in blood flow and therefore identifies regions of the brain that are particularly active during a given task.

functional tolerance

Decreased responding to a drug after repeated exposures, generally as a consequence of up- or down-regulation of receptors.

fundamental

The predominant frequency of an auditory tone or a visual scene.

fungiform papillae

One of three types of small structures on the tongue that contain taste receptors, located in the front of the tongue.

fusiform gyrus

A region on the inferior surface of the cortex, at the junction of temporal and occipital lobes, that has been associated with recognition of faces.

G protein-coupled receptors (GPCRs)

Cell surface receptors that, when activated extracellularly, initiate G protein signaling mechanisms inside the cell.

G proteins

A class of proteins that reside next to the intracellular portion of a receptor and that are activated when the receptor binds an appropriate ligand on the extracellular surface.

GABA

See gamma-aminobutyric acid.

gamete

A sex cell (sperm or ovum) that contains only unpaired chromosomes and therefore has only half the usual number of chromosomes in other cells.

gamma efferent

See gamma motor neuron.

gamma motor neuron

Also called gamma efferent. A motor neuron that innervates the contractile tissue (the intrafusal fiber) in a muscle spindle.

gamma-aminobutyric acid (GABA)

A widely distributed amino acid transmitter; the main inhibitory transmitter in the mammalian nervous system.

ganglion cells

A class of cells in the retina whose axons form the optic nerve.

gap junction

See electrical synapse.

gas neurotransmitter

A soluble gas, such as nitric oxide or carbon monoxide, that is produced and released by a neuron to alter the functioning of another neuron.

gel electrophoresis

A method of separating molecules of differing size or electrical charge by forcing them to flow through a gel.

gene

A length of DNA that encodes the information for constructing a particular protein.

gene amplification

See polymerase chain reaction.

general anesthetic

A drug that renders an individual unconscious.

generator potential

See receptor potential.

genetics

The study of inheritance, including the genes encoded in DNA.

genome

Also called genotype. All the genetic information that one specific individual has inherited.

genus

A group of species that resemble each other because of shared inheritance.

GH

See growth hormone.

ghrelin

A peptide hormone emanating from the gut.

glial cells

Also called glia or neuroglia. Nonneuronal brain cells that provide structural, nutritional, and other types of support to the brain.

global aphasia

The total loss of ability to understand language or to speak, read, or write.

globus pallidus

One of the basal ganglia.

glomerulus

A complex arbor of dendrites from a group of olfactory cells.

glucagon

A hormone, released by alpha cells in the islets of Langerhans, that increases blood glucose.

glucocorticoids

A class of steroid hormones, released by the adrenal cortex, that affect carbohydrate metabolism and inflammation.

glucodetector

A cell that detects and informs the nervous system about levels of circulating glucose.

gluconeogenesis

The metabolism of body fats and proteins to create glucose.

glucose

A sugar molecule used by the body and brain for energy.

glucose transporter

A molecule that conducts glucose molecules through the external membrane of a cell for use inside.

glutamate

An amino acid transmitter, the most common excitatory transmitter.

glutamate hypothesis

The hypothesis that schizophrenia may be caused, in part, by understimulation of glutamate receptors.

glutamatergic

Referring to cells that use glutamate as their synaptic transmitter.

glycine

An amino acid transmitter, often inhibitory.

glycogen

A complex carbohydrate derived from glucose.

glycogenesis

The physiological process by which glycogen is produced.

glycogenolysis

The conversion of glycogen back into glucose, triggered when blood concentrations of glucose drop too low.

GnIH

See gonadotropin-inhibiting hormone.

GnRH

See gonadotropin-releasing hormone.

goiter

A swelling of the thyroid gland resulting from iodine deficiency.

Goldman equation

An equation predicting the potential difference across a membrane based on the concentrations of ions on opposite sides of the membrane, as well as its relative permeability to each ion.

Golgi stain

A cell stain that fills a small proportion of neurons with a dense dark product.

Golgi tendon organ

One of the receptors located in tendons that send action potentials to the central nervous system reporting muscle tension.

gonadotropin

An anterior pituitary hormone that selectively stimulates the cells of the gonads to produce sex steroids and gametes.

gonadotropin-inhibiting hormone (GnIH)

A hypothalamic peptide hormone that reduces gonadotropin secretion from the pituitary.

gonadotropin-releasing hormone (GnRH)

A hypothalamic hormone that controls the release of luteinizing hormone and follicle-stimulating hormone from the pituitary.

gonads

The sexual organs (ovaries in females, testes in males), which produce gametes for reproduction.

grammar

All of the rules for usage of a particular language.

grand mal seizure

See tonic-clonic seizure.

granule cell

A type of small nerve cell.

gray matter

Areas of the brain that are dominated by cell bodies and are devoid of myelin.

grid cell

A neuron that selectively fires when an animal crosses the intersection points of an abstract grid map of the local environment.

gRNA

See guide RNA.

gross neuroanatomy

Anatomical features of the nervous system that are apparent to the naked eye.

growth cone

The growing tip of an axon or a dendrite.

growth hormone (GH)

Also called somatotropin or somatotropic hormone. A tropic hormone, secreted by the anterior pituitary, that influences the growth of cells and tissues.

guevedoces

Literally, “ eggs at 12” (in Spanish). A nickname for individuals who are raised as girls but at puberty change appearance and begin behaving as boys do.

guide RNA (gRNA)

A strand of RNA designed to hybridize with a targeted nucleotide sequence in DNA in order to guide the Cas9 enzyme to break the DNA at that site.

gustatory system

The taste system.

gut microbiota

Also called normal flora. The microorganisms that normally inhabit the digestive tract.

gyrus

A ridged or raised portion of a convoluted brain surface.

habituation

A form of nonassociative learning in which an organism becomes less responsive following repeated presentations of a stimulus.

hair cell

A cochlear auditory receptor cell.

hallucinogens

A class of drugs that alter sensory perception and produce peculiar experiences.

halorhodopsin

A protein that, in response to light of the proper wavelength, opens a channel to admit chloride ions, which results in inhibition of neurons.

hard problem of consciousness

The problem of how to read people’s subjective experience of consciousness and determine the qualia that accompany perception.

harmonics

Multiples of a particular frequency called the fundamental.

health psychology

Also called behavioral medicine. A field that studies psychological influences on health-related processes, such as why people become ill or how they remain healthy.

hearing loss

Decreased sensitivity to sound, in varying degrees.

Hebbian synapse

A synapse that is strengthened when it successfully drives the postsynaptic cell.

hemiparesis

Weakness of one side of the body.

hemiplegia

Partial paralysis involving one side of the body.

hemispatial neglect

A syndrome in which the person fails to pay any attention to objects presented to one side of the body and may even deny connection with that side.

hermaphrodite

An individual possessing the reproductive organs of both sexes, either simultaneously or at different points in time.

heroin

Diacetylmorphine; an artificially modified, very potent form of morphine.

hertz (Hz)

Cycles per second, as of an auditory stimulus.

hindbrain

Also called rhombencephalon. The rear division of the brain, which in the mature vertebrate contains the cerebellum, pons, and medulla.

hippocampus

A medial temporal lobe structure that is important for learning and memory.

histology

The scientific study of the composition of tissues.

homeostatic

Referring to the active process of maintaining a particular physiological parameter relatively constant.

hominin

The subgroup of Hominidae that contains modern humans and their ancestral species.

homology

A physical resemblance that is based on common ancestry, such as the similarity in forelimb structures of different mammals.

homoplasy

A physical resemblance between physical or behavioral characteristics due to convergent evolution, such as the similar body forms of tuna and dolphins.

horizontal cells

Specialized retinal neurons that contact both the receptor cells and the bipolar cells.

horizontal plane

The plane that divides the body or brain into upper and lower parts. Compare coronal plane and sagittal plane.

hormone

A chemical secreted by cells that is conveyed by the bloodstream and regulates target organs or tissues.

hostility

In psychology, the angry, antagonistic personality characteristic associated with a greater risk for heart disease.

hue

A dimension of light perception, varying around the color circle through blue, green, yellow, orange, and red.

hunger

The internal state of an animal seeking food.

huntingtin

A protein produced by a gene (called HTT) that, when containing too many trinucleotide repeats, results in Huntington’s disease in a carrier.

Huntington’s disease

Also called Huntington’s chorea. A progressive genetic disorder characterized by abrupt, involuntary movements and profound changes in mental functioning.

hybridization

The process by which a string of nucleotides becomes linked to a complementary series of nucleotides.

hyperphagia

Excessive eating.

hyperpolarization

An increase in membrane potential (the interior of the neuron becomes even more negative).

hypertonic

Referring to a solution with a higher concentration of salt than that found in interstitial fluid and blood plasma (more than about 0.9% salt).

hypodermis

Also called subcutaneous tissue. The innermost layer of skin, under the dermis.

hypofrontality hypothesis

The hypothesis that schizophrenia may result from underactivation of the frontal lobes.

hypophyseal portal system

A system of capillaries spanning between the neurosecretory cells of the hypothalamus and the secretory tissue of the anterior pituitary.

hypophysis

See pituitary gland.

hypothalamus

Part of the diencephalon, lying ventral to the thalamus.

hypotonic

Referring to a solution with a lower concentration of salt than that found in interstitial fluid and blood plasma (less than about 0.9% salt).

hypovolemic thirst

A desire to ingest fluids that is stimulated by a reduced volume of extracellular fluid.

hypoxia

A lack of oxygen.

Hz

See hertz.

IAPs

See inhibitors of apoptosis proteins.

IC

See impoverished condition.

ideational apraxia

An impairment in the ability to carry out a sequence of actions, even though each element or step can be done correctly.

ideomotor apraxia

The inability to carry out a simple motor activity in response to a verbal command, even though this same activity is readily performed spontaneously.

IHC

See immunohistochemistry and inner hair cell.

immunocytochemistry (ICC)

A method for detecting a particular protein in tissues in which an antibody recognizes and binds to the protein and then chemical methods are used to leave a visible reaction product around each antibody.

immunoglobulin

See antibody.

immunohistochemistry (IHC)

A technique in which labeled antibodies are used to visualize the histological distribution of specific proteins.

impoverished condition (IC)

Also called isolated condition. A condition in which a laboratory rodent is housed singly in a small cage without complex stimuli.

in situ hybridization

A method to detect cells that express specific messenger RNA transcripts by using a labeled nucleotide probe that is complementary to, and will therefore hybridize with, the transcript of interest.

in vitro

Literally, “ in glass” (in Latin). Outside the body, usually in a laboratory dish.

inattentional blindness

The failure to perceive nonattended stimuli that seem so obvious as to be impossible to miss.

incus

Latin for “ anvil.” A middle-ear bone situated between the malleus and the stapes.

independent variable

The factor that is manipulated by an experimenter.

indifferent gonads

The undifferentiated gonads of the early vertebrate fetus, which will eventually develop into either testes or ovaries.

individual response stereotypy

The tendency of individuals to show the same response pattern to particular situations throughout their life span.

indoleamine neurotransmitters

A class of monoamines, including serotonin and melatonin, that serve as neurotransmitters.

induction

The process by which one set of cells influences the fate of neighboring cells, usually by secreting a chemical factor that changes gene expression in the target cells.

inferior

In anatomy, pertaining to the lower of two locations. Compare superior.

inferior colliculi

Paired gray matter structures of the dorsal midbrain that receive auditory information.

infradian

Referring to a rhythmic biological event whose period is longer than that of a circadian rhythm— that is, longer than a day.

infrasound

Very low-frequency sound, generally below the threshold for human hearing (about 20 Hz).

infundibulum

See pituitary stalk.

inhibition of return

The phenomenon in which detection of stimuli at the former location of a cue is impaired for latencies of 200 ms or more.

inhibitors of apoptosis proteins (IAPs)

A family of proteins that inhibit caspases and thereby stave off apoptosis.

inhibitory postsynaptic potential (IPSP)

A hyperpolarizing potential in the postsynaptic neuron that is caused by inhibitory connections. IPSPs decrease the probability that the postsynaptic neuron will fire an action potential.

inner ear

The cochlea and vestibular apparatus.

inner hair cell (IHC)

One of the two types of cochlear receptor cells for hearing.

innervate

To provide neural input.

innervation ratio

The ratio expressing the number of muscle fibers innervated by a single motor axon.

inositol triphosphate (IP3)

A member of a class of second-messenger compounds (phosphoinositides) common in postsynaptic cells.

input zone

The part of a neuron that receives information from other neurons or from specialized sensory structures, usually corresponding to the cell’s dendrites.

instrumental conditioning

See operant conditioning.

insula

A region of cortex lying below the surface, within the lateral sulcus, of the frontal, temporal, and parietal lobes.

insulin

A hormone, released by beta cells in the islets of Langerhans, that lowers blood glucose.

integration zone

The part of the neuron that initiates nerve electrical activity, usually corresponding to the neuron’s axon hillock. It is described in detail in Chapter 3.

intellectual disability

A disability characterized by significant limitations in intellectual functioning and adaptive behavior.

intensity differences

Perceived differences in loudness between the two ears, which can be used to localize a sound source.

intermale aggression

Aggression between males of the same species.

intermediate-term memory (ITM)

A form of memory that lasts longer than short-term memory, but not as long as long-term memory.

internal fertilization

The process by which sperm fertilize eggs inside the female’s body, as in all mammals, birds, and reptiles.

interneuron

A neuron that is neither a sensory neuron nor a motor neuron but receives input from and sends output to other neurons.

intersex

Referring to an individual with atypical genital development and sexual differentiation that generally resembles a form intermediate between typical male and typical female genitals.

intracellular compartment

The fluid space of the body that is contained within cells.

intracellular fluid

Also called cytoplasm. The watery solution found within cells.

intrafusal fiber

One of the small muscle fibers that lie within each muscle spindle.

intraparietal sulcus (IPS)

A region in the human parietal lobe, homologous with the monkey lateral intraparietal area, that is especially involved in voluntary, top-down control of attention.

intrinsic activity

See efficacy.

intromission

Insertion of the erect penis into the vagina during copulation.

inverse agonist

A substance that binds to a receptor and causes it to do the opposite of what the naturally occurring transmitter does.

ion

An atom or molecule that has acquired an electrical charge by gaining or losing one or more electrons.

ion channel

A pore in the cell membrane that permits the passage of certain ions through the membrane when the channel is open.

ionotropic receptor

A receptor protein that includes an ion channel that is opened when the receptor is bound by an agonist.

IP3

See inositol triphosphate.

IPS

See intraparietal sulcus.

ipsilateral

In anatomy, pertaining to a location on the same side of the body. Compare contralateral.

IPSP

See inhibitory postsynaptic potential.

iris

The circular structure of the eye that provides an opening to form the pupil.

isolated brain

Sometimes referred to by the French term encéphale isolé. An experimental preparation in which an animal’s brainstem has been separated from the spinal cord by a cut below the medulla.

isolated condition

See impoverished condition.

isolated forebrain

Sometimes referred to by the French term cerveau isolé. An experimental preparation in which an animal’s nervous system has been cut in the upper midbrain, dividing the forebrain from the brainstem.

isotonic

Referring to a solution with a concentration of salt that is the same as that found in interstitial fluid and blood plasma (about 0.9% salt).

James-Lange theory

The theory that our experience of emotion is a response to the physiological changes that accompany it.

K complex

A sharp negative EEG potential that is seen in stage 2 sleep.

K⁺

See potassium ion.

ketamine

A dissociative anesthetic drug, similar to PCP, that acts as an NMDA receptor antagonist.

ketones

A metabolic fuel source liberated by the breakdown of body fats and proteins.

khat

Also spelled qat. An African shrub that, when chewed, acts as a stimulant.

kindling

A method of experimentally inducing an epileptic seizure by repeatedly stimulating a brain region.

kisspeptin

A hypothalamic peptide hormone that increases gonadotropin secretion by facilitating the release of gonadotropin-releasing hormone.

Kl&umml;ver-Bucy syndrome

A condition, brought about by bilateral amygdala damage, that is characterized by dramatic emotional changes including reduction in fear and anxiety.

knee-jerk reflex

A variant of the stretch reflex in which stretching of the tendon below the knee leads to an upward kick of the leg.

knockout organism

An individual in which a particular gene has been disabled by an experimenter.

Korsakoff’s syndrome

A memory disorder, related to a thiamine deficiency, that is generally associated with chronic alcoholism.

labeled lines

The concept that each nerve input to the brain reports only a particular type of information.

lamellated corpuscle

See Pacinian corpuscle.

language

The most sophisticated form of communication, in which a set of arbitrary sounds, tokens, or symbols can be arranged according to a grammar in order to convey an almost limitless variety of concepts.

latency differences

Differences between the two ears in the time of arrival of a sound, which can be employed by the nervous system to localize sound sources.

latent learning

Learning that has taken place but has not (yet) been demonstrated by performance.

lateral

In anatomy, toward the side of the body. Compare medial.

lateral geniculate nucleus (LGN)

The part of the thalamus that receives information from the optic tract and sends it to visual areas in the occipital cortex.

lateral hypothalamus (LH)

A hypothalamic region involved in the control of appetite and other functions.

lateral inhibition

The phenomenon by which interconnected neurons inhibit their neighbors, producing contrast at the edges of regions.

lateral intraparietal area (LIP)

A region in the monkey parietal lobe, homologous with the human intraparietal sulcus, that is especially involved in voluntary, top-down control of attention.

lateral sulcus

See Sylvian fissure.

lateral ventricle

A complexly shaped lateral portion of the ventricular system within each hemisphere of the brain.

lateralization

The tendency for the right and left halves of a system to differ from one another.

lateral-line system

A sensory system, found in many kinds of fishes and some amphibians, that informs the animal of water motion in relation to the body surface.

late-selection model

A model of attention in which the attentional bottleneck filters out stimuli only after substantial analysis has occurred.

l-dopa

The immediate precursor of the transmitter dopamine.

learned helplessness

In the context of experimentation, a learning paradigm in which individuals are subjected to inescapable, unpleasant conditions.

learning

The process of acquiring new and relatively enduring information, behavior patterns, or abilities, characterized by modifications of behavior as a result of practice, study, or experience.

lens

A structure in the eye that helps focus an image on the retina.

leptin

A peptide hormone released by fat cells.

lesions

Regions of damage.

levels of analysis

The scope of experimental approaches. A scientist may try to understand behavior by monitoring molecules, nerve cells, brain regions, or social environments, or some combination of these levels of analysis.

LGN

See lateral geniculate nucleus.

LH

See lateral hypothalamus and luteinizing hormone.

lie detector

See polygraph.

ligand

A substance that binds to receptor molecules, such as those at the surface of the cell.

ligand-gated ion channel

Also called chemically gated ion channel. An ion channel that opens or closes in response to the presence of a particular chemical.

limbic system

A loosely defined, widespread group of brain nuclei that innervate each other to form a network. These nuclei are implicated in emotions.

LIP

See lateral intraparietal area.

lipid bilayer

The structure of the neuronal cell membrane, which consists of two layers of lipid molecules. Various specialized proteins, such as ion channels and receptors, are embedded within the membrane.

lipids

Large molecules (commonly called fats) consisting of fatty acids and glycerol that are insoluble in water.

lithium

An element that, when administered as a drug, often relieves the symptoms of bipolar disorder.

lobotomy

The surgical detachment of a portion of the frontal lobe from the rest of the brain. It was once used as a treatment for schizophrenia and many other ailments.

local anesthetic

A drug, such as procaine or lidocaine, that blocks sodium channels to stop neural transmission in pain fibers.

local potential

An electrical potential that is initiated by stimulation at a specific site and that is a graded response that spreads passively across the cell membrane, decreasing in strength with time and distance.

locus coeruleus

Literally, “ blue spot.” A small nucleus in the brainstem whose neurons produce norepinephrine.

long-term memory (LTM)

An enduring form of memory that lasts days, weeks, months, or years and has a very large capacity.

long-term potentiation (LTP)

A stable and enduring increase in the effectiveness of synapses following repeated strong stimulation.

lordosis

A female receptive posture in quadrupeds in which the hindquarters are raised and the tail is turned to one side, facilitating intromission by the male.

Lou Gehrig’s disease

See amyotrophic lateral sclerosis.

loudness

The subjective experience of the pressure level of a sound.

loxP

A specific sequence of nucleotides recognized by the enzyme Cre-recombinase. If the enzyme encounters a pair of loxP sites in a gene, it will remove the DNA between the two sites and recombine the gene, usually rendering the gene product dysfunctional.

LSD

Also called acid. Lysergic acid diethylamide, a hallucinogenic drug.

LTM

See long-term memory.

LTP

See long-term potentiation.

lumbar

Referring to the five spinal segments that make up the upper part of the lower back.

luteinizing hormone (LH)

A gonadotropin, named for its stimulatory effects on the ovarian corpora lutea.

M1

See primary motor cortex.

macular degeneration

A progressive loss of central vision due to death or obstruction of photoreceptors in the retina.

mad cow disease

See bovine spongiform encephalopathy.

magnetic resonance imaging (MRI)

A noninvasive technique that uses magnetic energy to generate images that reveal some structural details in the living brain.

magnetoencephalography (MEG)

A passive and noninvasive functional brain-imaging technique that measures the tiny magnetic fields produced by active neurons, in order to identify regions of the brain that are particularly active during a given task.

magnocellular

Referring to relatively large cells.

malleus

Latin for “ hammer.” A middle-ear bone that is connected to the tympanic membrane.

mammillary body

One of a pair of nuclei at the base of the brain that connect to the hippocampus and play a role in memory.

MAO

See monoamine oxidase.

marijuana

Dried leaves and flowers of the plant Cannabis sativa, typically smoked to obtain THC for a psychoactive effect.

MBSR

See mindfulness-based stress reduction.

MC4Rs

See melanocortin type-4 receptors.

MD

See muscular dystrophy.

MDMA

Also called Ecstasy. A drug of abuse, 3,4-methylenedioxymethamphetamine.

medial

In anatomy, toward the middle of an organ or organism. Compare lateral.

medial amygdala

A portion of the amygdala that receives olfactory and pheromonal information.

medial forebrain bundle

A collection of axons traveling in the midline region of the forebrain.

medial geniculate nuclei

Nuclei in the thalamus that receive input from the inferior colliculi and send output to the auditory cortex.

medial preoptic area (mPOA)

A region of the anterior hypothalamus implicated in the control of many behaviors, including thermoregulation, sexual behavior, and gonadotropin secretion.

median eminence

Midline feature on the base of the brain marking the point at which the pituitary stalk exits the hypothalamus to connect to the pituitary. It contains elements of the hypophyseal portal system.

medulla

Also called myelencephalon. The posterior part of the hindbrain, continuous with the spinal cord.

medullary reticular formation

The hindmost portion of the brainstem reticular formation, implicated in motor control and copulatory behavior.

MEG

See magnetoencephalography.

Meissner’s corpuscle

A skin receptor cell type that detects light touch.

melanocortin type-4 receptors (MC4Rs)

A specific subtype of melanocortin receptor.

melanocortins

One category of endogenous opioid peptides.

melanopsin

A photopigment found within particular retinal ganglion cells that project to the suprachiasmatic nucleus.

melatonin

An amine hormone that is released by the pineal gland.

memory

1. The ability to retain information, based on the mental process of learning or encoding, retention across some interval of time, and retrieval or reactivation of the memory. 2. The specific information that is stored in the brain.

meninges

The three protective sheets of tissue— dura mater, pia mater, and arachnoid— that surround the brain and spinal cord.

meningiomas

Several classes of noncancerous tumors arising from the meninges.

meningitis

An acute inflammation of the meninges, usually caused by a viral or bacterial infection.

Merkel’s disc

A skin receptor cell type that detects fine touch.

mesencephalon

See midbrain.

mesolimbocortical pathway

A set of dopaminergic axons arising in the midbrain and innervating the limbic system and cortex.

mesostriatal pathway

A set of dopaminergic axons arising from the midbrain and innervating the basal ganglia, including those from the substantia nigra to the striatum.

messenger RNA (mRNA)

A strand of RNA that carries the code of a section of a DNA strand to the cytoplasm.

metabolic tolerance

The form of drug tolerance that arises when repeated exposure to the drug causes the metabolic machinery of the body to become more efficient at clearing the drug.

metabotropic receptor

A receptor protein that does not contain an ion channel but may, when activated, use a G protein system to alter the functioning of the postsynaptic cell.

metencephalon

A subdivision of the hindbrain that includes the cerebellum and the pons.

methylation

A chemical modification of DNA that does not affect the nucleotide sequence of a gene but makes that gene less likely to be expressed.

microbiome

The collective term for the population of microbes found in the gut.

microelectrode

An especially small electrode used to record electrical potentials from living cells.

microglial cells

Also called microglia. Extremely small glial cells that remove cellular debris from injured or dead cells.

micropolygyria

A condition of the brain in which small regions are characterized by more gyri than usual.

midbrain

Also called mesencephalon. The middle division of the brain.

middle canal

See scala media.

middle cerebral arteries

Two large arteries, arising from the internal carotid arteries, that provide blood to most of the lateral surfaces of the cerebral hemispheres.

middle ear

The cavity between the tympanic membrane and the cochlea.

migraines

Intense headaches, typically perceived from one half of the head, that recur regularly and can be difficult to treat.

milk letdown reflex

The reflexive release of milk in response to suckling or to stimuli associated with suckling.

millivolt (mV)

A thousandth of a volt.

mindfulness-based stress reduction (MBSR)

A therapy to reduce stress that pairs relaxation with efforts to focus attention on the present moment, rather than past or future problems.

mineralocorticoids

A class of steroid hormones, released by the adrenal cortex, that affect ion concentrations in body tissues.

minimal discriminable frequency difference

The smallest change in frequency that can be detected reliably between two tones.

minor traumatic brain injury (mTBI)

See concussion.

mirror neuron

A neuron that is active both when an individual makes a particular movement and when that individual sees another individual make that same movement.

mitochondrion

A cellular organelle that provides metabolic energy for the cell’s processes.

mitosis

The process of division of somatic cells that involves duplication of DNA.

mitral cell

A type of cell in the olfactory bulb that conducts smell information from the glomeruli to the rest of the brain.

modulatory site

A portion of a receptor that, when bound by a compound, alters the receptor’s response to its transmitter.

monoamine hormones

See amine hormones.

monoamine hypothesis

The hypothesis that depression is caused by reduced activity of one or more monoamine transmitters, such as serotonin.

monoamine oxidase (MAO)

An enzyme that breaks down and thereby inactivates monoamine transmitters.

monocular deprivation

Depriving one eye of light.

monopolar neuron

See unipolar neuron.

monozygotic

Referring to twins derived from a single fertilized egg (identical twins). Such individuals have the same genotype.

morpheme

The smallest grammatical unit of a language; a word or meaningful part of a word.

morphine

An opiate compound derived from the poppy flower.

motion sickness

The experience of nausea brought on by unnatural passive movement, as in a car or boat.

motivation

With respect to homeostasis, a psychological drive state that prompts behaviors that restore balance.

motoneuron

See motor neuron.

motor nerve

A nerve that conveys neural activity to muscle tissue and causes it to contract.

motor neuron

Also called motoneuron. A neuron in the brain or spinal cord that transmits motor messages, stimulating a muscle or gland.

motor plan

Also called motor program. A plan for action in the nervous system.

motor program

See motor plan.

motor protein

A specialized kinetic protein molecule that conveys a load, such as a vesicle, from one location to another within a cell.

motor theory of language

The theory proposing that the left-hemisphere language zones are motor control systems that are concerned with both the precise production and the perception of the extremely complex movements that go into speech.

motor unit

A single motor axon and all the muscle fibers that it innervates.

mPOA

See medial preoptic area.

MRI

See magnetic resonance imaging.

mRNA

See messenger RNA.

mTBI

See concussion.

m&umml;llerian ducts

A duct system in the embryo that will develop into female reproductive structures (oviduct, uterus, and inner vagina) if testes are not present.

multiple sclerosis

Literally, “ many scars.” A disorder characterized by widespread degeneration of myelin.

multipolar neuron

A nerve cell that has many dendrites and a single axon.

muscarinic

Referring to cholinergic receptors that respond to the chemical muscarine as well as to acetylcholine.

muscle fiber

A collection of large cylindrical cells, making up most of a muscle, that can contract in response to neurotransmitter released from a motor neuron.

muscle spindle

A muscle receptor that lies parallel to a muscle and sends action potentials to the central nervous system when the muscle is stretched.

muscular dystrophy (MD)

A disease that leads to degeneration of and functional changes in muscles.

musth

An annual period of heightened aggressiveness and sexual activity in male elephants.

mutation

A change in the nucleotide sequence of a gene as a result of unfaithful replication.

mV

See millivolt.

myasthenia gravis

A disorder characterized by a profound weakness of skeletal muscles, caused by a loss of acetylcholine receptors.

myelencephalon

See medulla.

myelin

The fatty insulation around an axon, formed by glial cells, that improves the speed of conduction of action potentials.

myelination

The process of myelin formation.

myopia

Nearsightedness; the inability to focus the retinal image of objects that are far away.

myosin

A protein that, along with actin, mediates the contraction of muscle fibers.

N1 effect

A negative deflection of the event-related potential, occurring about 100 ms after stimulus presentation, that is enhanced for selectively attended input, compared with ignored input.

Na⁺

See sodium ion.

naloxone

A potent antagonist of opiates that is often administered to people who have taken drug overdoses. It blocks receptors for endogenous opioids.

narcolepsy

A disorder that involves frequent, intense episodes of sleep, which last from 5 to 30 minutes and can occur anytime during the usual waking hours.

natriuretic polypeptide B (Nppb)

A peptide neurotransmitter used by neurons reporting itch to the spinal cord.

naturalist

A student of the forms and classification of organisms.

Na_V1.7

Also called SCN9A. A voltage-gated sodium channel used almost exclusively by nociceptors to initiate action potentials.

NE

See norepinephrine.

negative feedback

The property by which some of the output of a system feeds back to reduce the effect of input signals.

negative polarity

A negative electrical-potential difference relative to a reference electrode.

negative symptom

In psychiatry, a symptom that reflects insufficient functioning. Examples include emotional and social withdrawal, blunted affect, and slowness and impoverishment of thought and speech.

neocortex

Cerebral cortex that is made up of six distinct layers.

neologism

An entirely novel word, sometimes produced by a person with aphasia.

neonatal

Referring to newborns.

Nernst equation

An equation predicting the equilibrium potential for a given ion based on the concentrations of the ion on opposite sides of a permeable membrane.

nerve

A collection of axons bundled together outside the central nervous system.

nerve cell

See neuron.

nerve growth factor (NGF)

A substance that markedly affects the growth of neurons in spinal ganglia and in the ganglia of the sympathetic nervous system.

neural chain

A simple kind of neural circuit in which neurons are attached linearly, end to end.

neural groove

In the developing embryo, the groove between the neural folds.

neural tube

An embryonic structure with subdivisions that correspond to the future forebrain, midbrain, and hindbrain.

neurochemistry

The branch of neuroscience concerned with the fundamental chemical composition and processes of the nervous system.

neurocrine

Referring to secretory functions of neurons, especially pertaining to synapse transmission.

neuroeconomics

The study of brain mechanisms at work during decision making.

neuroendocrine cell

Also called neurosecretory cell. A neuron that releases hormones into local or systemic circulation.

neurofibrillary tangle

An abnormal whorl of neurofilaments within nerve cells.

neurogenesis

The mitotic division of nonneuronal cells to produce neurons.

neuroglia

See glial cells.

neurohypophysis

See posterior pituitary.

neuroleptics

See antipsychotics.

neuromodulator

A substance that influences the activity of synaptic transmitters.

neuromuscular junction (NMJ)

The region where the motor neuron terminal and the adjoining muscle fiber meet; the point where the nerve transmits its message to the muscle fiber.

neuron

Also called nerve cell. The basic unit of the nervous system, each composed of a cell body, receptive extension(s) (dendrites), and a transmitting extension (axon).

neuron doctrine

The hypothesis that the brain is composed of separate cells that are distinct structurally, metabolically, and functionally.

neuropathic pain

Pain caused by damage to peripheral nerves. It is often difficult to treat.

neuropeptide

Also called peptide neurotransmitter. A peptide that is used by neurons for signaling.

neuropeptide Y (NPY)

A peptide neurotransmitter that may carry some of the signals for feeding.

neuropharmacology

Also called psychopharmacology. The scientific field concerned with the discovery and study of compounds that selectively affect the functioning of the nervous system.

neurophysiology

The study of electrical and chemical processes in neurons.

neuroplasticity

Also called neural plasticity. The ability of the nervous system to change in response to experience or the environment.

neuroscience

The study of the nervous system.

neurosecretory cell

See neuroendocrine cell.

neurosteroids

Steroid molecules produced within the brain that affect neurons.

neurotransmitter

Also called synaptic transmitter, chemical transmitter, or simply transmitter. The chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons.

neurotrophic factor

Also called trophic factor. A target-derived chemical that acts as if it “ feeds” certain neurons to help them survive.

neurotrophins

A family of proteins, including NGF and BDNF, that prevent different classes of neurons from dying.

NGF

See nerve growth factor.

nicotine

A compound found in plants, including tobacco, that acts as an agonist on a large class of cholinergic receptors.

nicotinic

Referring to cholinergic receptors that respond to nicotine as well as to acetylcholine.

night terror

A sudden arousal from stage 3 slow-wave sleep that is marked by intense fear and autonomic activation.

nightmare

A long, frightening dream that awakens the sleeper from REM sleep.

Nissl stain

A cell stain that reveals all cell bodies by staining RNA.

nitric oxide (NO)

A soluble gas that serves as a retrograde gas neurotransmitter in the nervous system.

NMDA receptor

A glutamate receptor that also binds the glutamate agonist NMDA (N-methyl-d-aspartate) and that is both ligand-gated and voltage-sensitive.

NMJ

See neuromuscular junction.

NO

See nitric oxide.

nociceptor

A receptor that responds to stimuli that produce tissue damage or pose the threat of damage.

nocturnal

Active during the dark periods of the daily cycle.

node of Ranvier

A gap between successive segments of the myelin sheath where the axon membrane is exposed.

nonassociative learning

A type of learning in which presentation of a particular stimulus alters the strength or probability of a response according to the strength and temporal spacing of that stimulus. It includes habituation and sensitization.

noncompetitive ligand

Also called neuromodulator. A substance that alters the response to an endogenous ligand without interacting with the endogenous ligand’s recognition site.

nondeclarative memory

Also called procedural memory. A memory that is shown by performance rather than by conscious recollection.

nondirected synapse

A type of synapse in which the presynaptic and postsynaptic cells are not in close apposition; instead, neurotransmitter is released by axonal varicosities and diffuses away to affect wide regions of tissue.

nonfluent aphasia

Also called Broca’s aphasia. A language impairment characterized by difficulty with speech production but not with language comprehension. It is related to damage in Broca’s area.

nonfluent speech

Talking with considerable effort, short sentences, and the absence of the usual melodic character of conversational speech.

nongenomic effect

An effect of a steroid hormone that is not mediated by direct changes in gene expression.

nonprimary motor cortex

Frontal lobe regions adjacent to the primary motor cortex that contribute to motor control and modulate the activity of the primary motor cortex.

nonprimary sensory cortex

See secondary sensory cortex.

non-REM (NREM) sleep

Stage of sleep without rapid eye movements. In humans this is divided into stages 1, 2, and 3 sleep.

nootropics

A class of drugs that enhance cognitive function.

noradrenaline

See norepinephrine.

noradrenergic

Referring to systems using norepinephrine (noradrenaline) as a transmitter.

norepinephrine (NE)

Also called noradrenaline. A chemical that acts as a transmitter in the brain and sympathetic nervous system, and also as a circulating adrenal hormone that prepares the body for action.

normal flora

See gut microbiota.

Northern blot

A method of detecting a particular RNA transcript in a tissue or organ by separating RNA from that source with gel electrophoresis, blotting the separated RNAs onto nitrocellulose, and then using a nucleotide probe to hybridize with, and highlight, the transcript of interest.

notochord

A midline structure arising early in the embryonic development of vertebrates.

Nppb

See natriuretic polypeptide B.

NPY

See neuropeptide Y.

NPY neurons

Neurons involved in the hypothalamic appetite control system, so named because they produce neuropeptide Y (NPY) along with agouti-related peptide (AgRP).

NREM 1

See stage 1 sleep.

NREM 2

See stage 2 sleep.

NREM 3

See slow-wave sleep.

NREM sleep

See non-REM (NREM) sleep.

NST

See nucleus of the solitary tract.

nucleotide

A portion of a DNA or RNA molecule that is composed of a single base and the adjoining sugar-phosphate unit of the strand.

nucleus

A collection of neurons within the central nervous system (e.g., the caudate nucleus).

nucleus accumbens

A region of the forebrain that receives dopaminergic innervation from the ventral tegmental area.

nucleus of the solitary tract (NST)

A brainstem nucleus that receives visceral and taste information via several cranial nerves.

nutrient

A chemical that is needed for growth, maintenance, and repair of the body but is not used as a source of energy.

obligatory losses

Unavoidable loss of regulated variables, such as energy, water, or temperature, as a consequence of life processes.

obsessive-compulsive disorder (OCD)

A syndrome in which the affected individual engages in recurring, repetitive acts that are carried out without rhyme, reason, or the ability to stop.

occipital lobe

Large region of cortex covering much of the posterior part of each cerebral hemisphere, specialized for visual processing.

OCD

See obsessive-compulsive disorder.

ocular dominance column

A region of cortex in which one eye or the other provides a greater degree of synaptic input.

ocular dominance histogram

A graph that portrays the strength of response of a brain neuron to stimuli presented to either the left eye or the right eye.

ocular dominance slab

A slab of visual cortex, about 0.5 mm wide, in which the neurons of all layers respond preferentially to stimulation of one eye.

oculomotor apraxia

A severe difficulty in voluntarily steering visual gaze toward specific targets.

off-center bipolar cell

A retinal bipolar cell that is inhibited by light in the center of its receptive field.

off-center ganglion cell

A retinal ganglion cell that is activated when light is presented to the periphery, rather than the center, of the cell’s receptive field.

off-center/on-surround

Referring to a concentric receptive field in which the center inhibits the cell of interest while the surround excites it.

OHC

See outer hair cell.

olfactory bulb

An anterior projection of the brain that terminates in the upper nasal passages and, through small openings in the skull, receives axons from olfactory receptor neurons.

olfactory epithelium

A sheet of cells, including olfactory receptors, that lines the dorsal portion of the nasal cavities and adjacent regions, including the septum that separates the left and right nasal cavities.

olfactory receptor neuron

A type of neuron, found in the olfactory epithelium, that senses airborne odorants via specialized receptor proteins.

oligodendrocyte

A type of glial cell that forms myelin in the central nervous system.

on-center bipolar cell

A retinal bipolar cell that is excited by light in the center of its receptive field.

on-center ganglion cell

A retinal ganglion cell that is activated when light is presented to the center, rather than the periphery, of the cell’s receptive field.

on-center/off-surround

Referring to a concentric receptive field in which the center excites the cell of interest while the surround inhibits it.

ontogeny

The process by which an individual changes in the course of its lifetime— that is, grows up and grows old.

Onuf’s nucleus

The human homolog of the spinal nucleus of the bulbocavernosus (SNB) in rats.

open-loop control mechanism

A control mechanism in which feedback from the output of the system is not provided to the input control.

operant conditioning

Also called instrumental conditioning. A form of associative learning in which the likelihood that an act (instrumental response) will be performed depends on the consequences (reinforcing stimuli) that follow it.

opiates

A class of compounds that exert an effect like that of opium, including reduced pain sensitivity.

opioid peptide

A type of endogenous peptide that mimics the effects of morphine in binding to opioid receptors and producing marked analgesia and reward.

opioid receptor

A receptor that responds to endogenous and/or exogenous opiates.

opioids

A class of peptides produced in various regions of the brain that bind to opioid receptors and act like opiates.

opium

A heterogeneous extract of the seedpod juice of the opium poppy, Papaver somniferum.

opponent-process hypothesis

The theory that color vision depends on systems that produce opposite responses to light of different wavelengths.

opsin

One of the two components of photopigments in the retina.

optic ataxia

A spatial disorientation in which the affected person is unable to accurately reach for objects using visual guidance.

optic chiasm

The point at which the two optic nerves meet.

optic disc

The region of the retina devoid of receptor cells because ganglion cell axons and blood vessels exit the eyeball there.

optic nerve

Cranial nerve II, the collection of ganglion cell axons that extend from the retina to the optic chiasm.

optic radiation

Axons from the lateral geniculate nucleus that terminate in the primary visual areas of the occipital cortex.

optic tract

The axons of retinal ganglion cells after they have passed the optic chiasm. Most terminate in the lateral geniculate nucleus.

optical imaging

A method for visualizing brain activity in which near-infrared light is passed through the scalp and skull.

optogenetics

The use of genetic tools to induce neurons to become sensitive to light, such that experimenters can excite or inhibit a cell by exposing it to light.

oral contraceptive

A birth control pill, typically consisting of steroid hormones to prevent ovulation.

orexigenic neurons

Neurons of the hypothalamic appetite system that promote feeding behavior.

orexins

Also called hypocretins. Neuropeptides produced in the hypothalamus that are involved in switching between sleep states, in narcolepsy, and in the control of appetite.

organ of Corti

A structure in the inner ear that lies on the basilar membrane of the cochlea and contains the hair cells and terminations of the auditory nerve.

organizational effect

A permanent alteration of the nervous system, and thus permanent change in behavior, resulting from the action of a steroid hormone on an animal early in its development.

organum vasculosum of the lamina terminalis (OVLT)

One of the circumventricular organs.

orgasm

The climax of sexual experience, marked by extremely pleasurable sensations.

orientation column

A column of visual cortex that responds to rod-shaped stimuli of a particular orientation.

orphan receptor

Any receptor for which no endogenous ligand has yet been discovered.

osmolality

The number of solute particles per unit volume of solvent.

osmosensory neuron

A specialized neuron that measures the movement of water into and out of cells.

osmosis

The passive movement of water molecules from one place to another until a uniform concentration is achieved.

osmotic pressure

The tendency of a solvent to move through a membrane in order to equalize the concentration of solute.

osmotic thirst

A desire to ingest fluids that is stimulated by a high concentration of solute (like salt) in the extracellular compartment, reducing intracellular fluid.

ossicles

Three small bones (incus, malleus, and stapes) that transmit sound across the middle ear, from the tympanic membrane to the oval window.

otoacoustic emission

A sound produced by the cochlea itself, either spontaneously or in response to an environmental noise.

otolith

A small crystal on the gelatinous membrane in the vestibular system.

ototoxic

Toxic to the ears, especially the middle or inner ear.

outer hair cell (OHC)

One of the two types of cochlear receptor cells for hearing.

output zone

The part of a neuron, usually corresponding to the axon terminals, at which the cell sends information to another cell.

oval window

The location on the surface of the cochlea at which vibrations are received from the ossicles.

ovaries

The female gonads, which produce eggs for reproduction.

OVLT

See organum vasculosum of the lamina terminalis.

ovulation

The production and release of an egg (ovum).

ovulatory cycle

The periodic occurrence of ovulation.

ovum

An egg, the female gamete.

oxytocin

A hormone, released from the posterior pituitary, that triggers milk letdown in the nursing female.

P1 effect

A positive deflection of the event-related potential, occurring 70– 100 ms after stimulus presentation, that is enhanced for selectively attended visual input, compared with ignored input.

P3 effect

A positive deflection of the event-related potential, occurring about 300– 500 ms after stimulus presentation, that is associated with higher-order auditory stimulus processing and late attentional selection.

Pacinian corpuscle

Also called lamellated corpuscle. A skin receptor cell type that detects vibration.

pain

The discomfort normally associated with tissue damage.

pair bond

A durable and exclusive relationship between a male and a female.

papilla

A small bump that projects from the surface of the tongue. Papillae contain most of the taste receptor cells.

parabiotic

Referring to a surgical preparation that joins two animals to share a single blood supply.

paracrine

Referring to cellular communication in which a chemical signal diffuses to nearby target cells through the extracellular space.

paradoxical sleep

See rapid-eye-movement (REM) sleep.

paragigantocellular nucleus (PGN)

A region of the brainstem reticular formation implicated in sleep and modulation of spinal reflexes.

parallel fiber

One of the axons of the granule cells that form the outermost layer of the cerebellar cortex.

paraphasia

A symptom of aphasia that is distinguished by the substitution of a word by a sound, an incorrect word, an unintended word, or a neologism (a meaningless word).

parasympathetic nervous system

A component of the autonomic nervous system that arises from both the cranial nerves and the sacral spinal cord.

paraventricular nucleus (PVN)

A nucleus of the hypothalamus implicated in the release of oxytocin and vasopressin, and in the control of feeding and other behaviors.

parental behavior

Behavior of adult animals with the goal of enhancing the well-being of their own offspring, often at some cost to the parents.

paresis

Partial paralysis.

parietal lobe

Large region of cortex lying between the frontal and occipital lobes of each cerebral hemisphere.

parkin

A protein that has been implicated in Parkinson’s disease.

Parkinson’s disease

A degenerative neurological disorder, characterized by tremors at rest, muscular rigidity, and reduction in voluntary movement, that involves dopaminergic neurons of the substantia nigra.

parthenogenesis

“ Virgin birth,” a process of reproduction by which a female produces live offspring without need of a male.

partial agonist

A drug that, when bound to a receptor, has less effect than the endogenous ligand would.

parvocellular

Referring to relatively small cells.

patch clamp

To use voltage clamping to monitor the flow of current across a tiny patch of membrane taken from a neuron.

patient H.M.

A person who, because of damage to medial temporal lobe structures, was unable to encode new declarative memories. Upon his death we learned his name was Henry Molaison.

patient K.C.

A person who sustained damage to the cortex that rendered him unable to form and retrieve new episodic memories, especially autobiographical memories. Upon his death we learned that his name was Kent Cochrane.

patient N.A.

A person who is unable to encode new declarative memories, because of damage to the dorsal thalamus and the mammillary bodies.

pattern coding

Coding of information in sensory systems based on the temporal pattern of action potentials.

Pavlovian conditioning

See classical conditioning.

PCP

See phencyclidine.

PCR

See polymerase chain reaction.

peptide

A short string of amino acids. Longer strings of amino acids are called proteins.

peptide hormones

A class of hormones, molecules of which consist of a string of amino acids. If the string of amino acids is long enough, it may be called a protein hormone.

peptide neurotransmitter

Also called neuropeptide. A neurotransmitter consisting of a short chain of amino acids. Examples include neuropeptide Y, galanin, and VIP (vasoactive intestinal polypeptide).

perceptual load

The immediate processing challenge presented by a stimulus.

periaqueductal gray

The neuronal body– rich region of the midbrain surrounding the cerebral aqueduct that connects the third and fourth ventricles. It is involved in pain perception.

period

The interval of time between two similar points of successive cycles, such as sunset to sunset.

peripheral nervous system

The portion of the nervous system that includes all the nerves and neurons outside the brain and spinal cord.

peripheral spatial cuing task

An attention task where a visual stimulus is preceded by a simple sensory stimulus (like a flash) that reflexively captures attention.

perseverate

To continue to show a behavior repeatedly.

PET

See positron emission tomography.

PGN

See paragigantocellular nucleus.

phagocyte

An immune system cell that engulfs invading molecules or microbes.

phallus

The clitoris or penis.

pharmacodynamics

Collective name for the factors that affect the relationship between a drug and its target receptors, such as affinity and efficacy.

pharmacokinetics

Collective name for all the factors that affect the movement of a drug into, through, and out of the body.

phase shift

A shift in the activity of a biological rhythm, typically provided by a synchronizing environmental stimulus.

phasic receptor

A receptor in which the frequency of action potentials drops rapidly as stimulation is maintained.

phencyclidine (PCP)

Also called angel dust. An anesthetic agent that is also a psychedelic drug. PCP makes many people feel dissociated from themselves and their environment.

phenotype

The sum of an individual’s physical characteristics at one particular time.

phenylketonuria (PKU)

An inherited disorder of protein metabolism in which the absence of an enzyme leads to a toxic buildup of certain compounds, causing intellectual disability.

pheromone

A chemical signal that is released outside the body of an animal and affects other members of the same species.

phobic disorder

An intense, irrational fear that becomes centered on a specific object, activity, or situation that a person feels compelled to avoid.

phoneme

A sound that is produced for language.

photon

A quantum of electromagnetic energy in the range of wavelengths we call light.

photopic system

A system in the retina that operates at high levels of light, shows sensitivity to color, and involves the cones.

photoreceptor adaptation

The tendency of rods and cones to adjust their light sensitivity to match ambient levels of illumination.

photoreceptors

Neural cells in the retina that respond to light.

phrenology

The outmoded belief that bumps on the skull reflect enlargements of brain regions responsible for certain behavioral faculties.

phylogeny

The evolutionary history of a particular group of organisms.

pia mater

The innermost of the three meninges that surround the brain and spinal cord.

Piezo2

A receptor protein in touch receptors that responds to mechanical stretch by opening channels to let cations in to depolarize the cell.

pineal gland

The secretory gland in the brain, at midline, that is the source of melatonin release.

pinna

The external part of the ear.

pitch

A dimension of auditory experience in which sounds vary from low to high.

pituitary gland

Also called hypophysis. A small, complex endocrine gland located in a socket at the base of the skull.

pituitary stalk

Also called infundibulum. A thin piece of tissue that connects the pituitary gland to the hypothalamus.

PKU

See phenylketonuria.

place cell

A neuron within the hippocampus that selectively fires when the animal is in a particular location.

place coding

The encoding of sound frequency as a function of the location on the basilar membrane that is most stimulated by that sound.

placebo

A substance that is known to be ineffective or inert, but when administered like a drug can sometimes brings relief.

planum temporale

A region of superior temporal cortex adjacent to the primary auditory area.

plegia

Paralysis, the loss of the ability to move.

polioviruses

A class of viruses that destroy motor neurons of the spinal cord and brainstem.

polygraph

Also called a lie detector. A device that measures several bodily responses, such as heart rate and blood pressure.

polymerase chain reaction (PCR)

Also called gene amplification. A method for reproducing a particular RNA or DNA sequence manyfold, allowing amplification for sequencing or manipulating the sequence.

polymodal

Involving several sensory modalities.

POMC neurons

Neurons involved in the hypothalamic appetite control system, so named because they produce pro-opiomelanocortin (POMC) along with cocaine- and amphetamine-related transcript (CART).

pons

A portion of the metencephalon; part of the brainstem connecting midbrain to medulla.

positive symptom

In psychiatry, a behavior that is gained in a disorder. Examples include hallucinations, delusions, and excited motor behavior in schizophrenia.

positron emission tomography (PET)

A technique for examining brain function by combining tomography with injections of radioactive substances used by the brain.

postcentral gyrus

The strip of parietal cortex, just behind the central sulcus, that receives somatosensory information from the entire body.

postcopulatory behavior

The final stage in mating behavior. Species-specific postcopulatory behaviors include rolling (in the cat) and grooming (in the rat).

posterior

Also called caudal. In anatomy, toward the tail end of an organism. Compare anterior.

posterior cerebral arteries

Two large arteries, arising from the basilar artery, that provide blood to posterior aspects of the cerebral hemispheres, cerebellum, and brainstem.

posterior pituitary

Also called neurohypophysis. The rear division of the pituitary gland.

postganglionic

Literally, “ after the ganglion.” Referring to neurons in the autonomic nervous system that run from the autonomic ganglia to various targets in the body.

postpartum depression

A bout of depression that afflicts a woman around the time that she gives birth.

postsynaptic

Referring to the region of a synapse that receives and responds to neurotransmitter.

postsynaptic membrane

The specialized membrane on the surface of the cell that receives information by responding to neurotransmitter from a presynaptic neuron.

postsynaptic potential

A local potential that is initiated by stimulation at a synapse, can vary in amplitude, and spreads passively across the cell membrane, decreasing in strength with time and distance.

posttraumatic stress disorder (PTSD)

Formerly called combat fatigue, war neurosis, or shell shock. A disorder in which memories of an unpleasant episode repeatedly plague the victim.

potassium ion (K⁺)

A potassium atom that carries a positive charge because it has lost one electron.

pragmatics

In linguistics, the context in which a speech sound is uttered.

precentral gyrus

The strip of frontal cortex, just in front of the central sulcus, that is crucial for motor control.

precocial

Referring to animals that are born in a relatively developed state and that are able to survive with relatively little maternal care.

prefrontal cortex

The anteriormost region of the frontal lobe.

preganglionic

Literally, “ before the ganglion.” Referring to neurons in the autonomic nervous system that run from the central nervous system to the autonomic ganglia.

premotor cortex

A region of nonprimary motor cortex just anterior to the primary motor cortex.

presenilin

An enzyme that cleaves amyloid precursor protein, forming β-amyloid, which can lead to Alzheimer’s disease.

prestin

A motor protein that allows outer hair cells to change length.

presynaptic

Referring to the region of a synapse that releases neurotransmitter.

presynaptic membrane

The specialized membrane of the axon terminal of the neuron that transmits information by releasing neurotransmitter.

primacy effect

The superior performance seen in a memory task for items at the start of a list. It is usually attributed to long-term memory.

primary auditory cortex (A1)

The region of superior temporal cortex in which auditory processing occurs.

primary motor cortex (M1)

The apparent executive region for the initiation of movement, primarily the precentral gyrus.

primary sensory cortex

For a given sensory modality, the region of cortex that receives most of the information about that modality from the thalamus or, in the case of olfaction, directly from the secondary sensory neurons.

primary sensory ending

Also called annulospiral ending. The axon that transmits information from the central portion of a muscle spindle.

primary somatosensory cortex (S1)

Also called somatosensory 1. The gyrus just posterior to the central sulcus, in the parietal lobe, where sensory receptors on the body surface are mapped; primary cortex for receiving touch and pain information.

primary visual cortex (V1)

Also called striate cortex or area 17. The region of the occipital lobe where most visual information first arrives in the cortex.

priming

Also called repetition priming. The phenomenon by which exposure to a stimulus facilitates subsequent responses to the same or a similar stimulus.

prion

A protein that can become improperly folded and thereby can induce other proteins to follow suit, leading to long protein chains that impair neural function.

probe

A manufactured sequence of DNA or RNA that is made to include a label (a colorful or radioactive molecule) that lets us track its location.

procedural memory

See nondeclarative memory.

proceptive

Referring to a state in which an animal advertises its readiness to mate through species-typical behaviors, such as ear wiggling in the female rat.

progesterone

The primary type of progestin secreted by the ovary.

progestins

A major class of steroid hormones that are produced by the ovary, including progesterone.

prolactin

A peptide hormone, produced by the anterior pituitary, that promotes mammary development for lactation in female mammals.

pro-opiomelanocortin (POMC)

A pro-hormone that can be cleaved to produce the melanocortins, which also participate in feeding control.

proprioception

Body sense; information about the position and movement of the body that is sent to the brain.

prosencephalon

See forebrain.

prosody

The perception of emotional tone-of-voice aspects of language.

prosopagnosia

Also called face blindness. A condition characterized by the inability to recognize faces.

protein

A long string of amino acids; the basic building material of organisms.

protein kinase

An enzyme that adds phosphate groups (PO4) to protein molecules, causing a functional change in the proteins.

proximal

In anatomy, near the trunk or center of an organism. Compare distal.

psychoneuroimmunology

The study of the immune system and its interaction with the nervous system and behavior.

psychopath

An individual incapable of experiencing remorse.

psychopharmacology

See neuropharmacology.

psychosocial dwarfism

Reduced stature caused by stress early in life that inhibits growth.

psychosomatic medicine

A field of study that emphasizes the role of psychological factors in disease.

psychosurgery

Surgery in which brain lesions are produced to alleviate severe psychiatric disorders.

psychotomimetic

A drug that induces a state resembling schizophrenia.

PTSD

See posttraumatic stress disorder.

pulvinar

In humans, the posterior portion of the thalamus, heavily involved in visual processing and direction of attention.

punch-drunk

See chronic traumatic encephalopathy.

pupil

The aperture, formed by the iris, that allows light to enter the eye.

pure tone

A tone with a single frequency of vibration.

Purkinje cell

A type of large nerve cell in the cerebellar cortex.

putamen

One of the basal ganglia.

PVN

See paraventricular nucleus.

pyramidal cell

A type of large nerve cell, found in the cerebral cortex, that has a roughly pyramid-shaped cell body.

pyramidal system

Also called corticospinal system. The motor system that includes neurons within the cerebral cortex that send axons to form the pyramidal tract.

PYY_{3– 36}

A peptide hormone, secreted by the intestines, that probably acts on hypothalamic appetite control mechanisms to suppress appetite.

quale

A purely subjective experience of perception.

quantum (pl. quanta)

A discrete unit of electromagnetic energy.

radial glial cells

Glial cells that form early in development, spanning the width of the emerging cerebral hemispheres, and guide migrating neurons.

radioimmunoassay (RIA)

A technique that uses antibodies to measure the concentration of a substance, such as a hormone, in blood.

range fractionation

A hypothesis of stimulus intensity perception stating that a wide range of intensity values can be encoded by a group of cells, each of which is a specialist for a particular range of stimulus intensities.

raphe nuclei

A string of nuclei in the midline of the midbrain and brainstem that contain most of the serotonergic neurons of the brain.

rapid-eye-movement (REM) sleep

Also called paradoxical sleep. A stage of sleep characterized by small-amplitude, fast-EEG waves, no postural tension, and rapid eye movements. REM rhymes with “ gem.”

RBD

See REM behavior disorder.

recency effect

The superior performance seen in a memory task for items at the end of a list. It is attributed to short-term memory.

receptive field

The stimulus region and features that affect the activity of a cell in a sensory system.

receptor cell

A specialized cell that responds to a particular energy or substance in the internal or external environment and converts this energy into a change in the electrical potential across its membrane.

receptor isoform

A subtype of a receptor protein whose slight differences in structure give it different functional properties.

receptor molecule

Also called receptor. A protein that binds and reacts to molecules of a neurotransmitter or hormone.

receptor potential

Also called generator potential. A local change in the resting potential of a receptor cell that mediates between the impact of stimuli and the initiation of action potentials.

receptor subtype

Any type of receptor having functional characteristics that distinguish it from other types of receptors for the same neurotransmitter.

reconsolidation

The return of a memory trace to stable long-term storage after it has been temporarily made volatile during the process of recall.

recovery of function

The recovery of behavioral capacity following brain damage from stroke or injury.

red nucleus

A brainstem structure related to motor control.

reductionism

The scientific strategy of breaking a system down into increasingly smaller parts in order to understand it.

reflex

A simple, highly stereotyped, and unlearned response to a particular stimulus (e.g., an eye blink in response to a puff of air).

reflexive attention

Also called exogenously controlled attention or bottom-up attention. The involuntary reorienting of attention toward the location of an unexpected object or event.

refraction

The bending of light rays by a change in the density of a medium, such as the cornea and the lens of the eye.

refractory

Referring to transiently inactivated or exhausted axonal membranes.

refractory period

A period following copulation during which an individual cannot recommence copulation.

regulation

An adaptive response to early injury, as when developing individual cells compensate for missing or injured cells.

relative refractory phase

A period of reduced sensitivity during which only strong stimulation produces an action potential.

releasing hormones

A class of hormones, produced in the hypothalamus, that traverse the hypothalamic-pituitary portal system to control the pituitary’s release of tropic hormones.

REM behavior disorder (RBD)

A sleep disorder in which a person physically acts out a dream.

REM sleep

See rapid-eye-movement (REM) sleep.

repetition priming

See priming.

reserpine

A drug that causes the depletion of monoamines and can lead to depression.

resting membrane potential

A difference in electrical potential across the membrane of a nerve cell during an inactive period.

reticular formation

An extensive region of the brainstem (extending from the medulla through the thalamus) that is involved in arousal (waking) and motor control.

reticulospinal tract

A tract of axons arising from the brainstem reticular formation and descending to the spinal cord to modulate movement.

retina

The receptive surface inside the eye that contains photoreceptors and other neurons.

retinal

Abbreviation for retinaldehyde, one of the two components of photopigments in the retina. Also called vitamin A aldehyde.

retinaldehyde

See retinal.

retinohypothalamic pathway

The projection of retinal ganglion cells to the suprachiasmatic nuclei.

retrieval

A process in memory during which a stored memory is used by an organism.

retrograde amnesia

Difficulty in retrieving memories formed before the onset of amnesia.

retrograde degeneration

Destruction of the nerve cell body following injury to its axon.

retrograde messenger

Transmitter that is released by the postsynaptic region, travels back across the synapse, and alters the functioning of the presynaptic neuron.

retrograde synapse

A synapse in which a signal (usually a gas neurotransmitter) flows from the postsynaptic neuron to the presynaptic neuron, thus counter to the usual direction of synaptic communication.

retrograde transmitter

A neurotransmitter that diffuses from the postsynaptic neuron back to the presynaptic neuron.

Rett syndrome

A rare genetic disorder, occurring almost exclusively in girls, of slowing development resulting in intellectual disability, stereotyped movements, and loss of language.

reuptake

The process by which released synaptic transmitter molecules are taken up and reused by the presynaptic neuron, thus stopping synaptic activity.

rhodopsin

The photopigment in rods that responds to light.

rhombencephalon

See hindbrain.

RIA

See radioimmunoassay.

ribonucleic acid (RNA)

A nucleic acid that implements information found in DNA.

ribosomes

Structures in the cell body where genetic information is translated to produce proteins.

rods

A class of light-sensitive receptor cells (photoreceptors) in the retina that are most active at low levels of light.

rostral

See anterior.

round window

A membrane separating the cochlear duct from the middle-ear cavity.

rubrospinal tract

A tract of axons arising from the red nucleus in the midbrain and innervating neurons of the spinal cord.

Ruffini’s ending

A skin receptor cell type that detects stretching of the skin.

S1

See primary somatosensory cortex.

S2

See secondary somatosensory cortex.

saccades

Fast movements of the eyes that present various parts of the visual scene to the fovea. When we fix our gaze, small saccades that we are unaware of avert photoreceptor adaptation.

saccule

A small, fluid-filled sac under the utricle in the vestibular system that responds to static positions of the head.

sacral

Referring to the five spinal segments that make up the lower part of the lower back.

SAD

See seasonal affective disorder.

sagittal plane

The plane that bisects the body or brain into right and left portions. Compare coronal plane and horizontal plane.

saltatory conduction

The form of conduction that is characteristic of myelinated axons, in which the action potential jumps from one node of Ranvier to the next.

saxitoxin (STX)

An animal toxin that blocks sodium channels when applied to the outer surface of the cell membrane.

SC

See standard condition.

scala media

Also called middle canal. The central of the three canals running the length of the cochlea, situated between the scala vestibuli and the scala tympani.

scala tympani

Also called tympanic canal. One of the three canals running the length of the cochlea.

scala vestibuli

Also called vestibular canal. One of the three canals running the length of the cochlea.

schizophrenia

A severe psychopathology characterized by negative symptoms such as emotional withdrawal and impoverished thought, and by positive symptoms such as hallucinations and delusions.

Schwann cell

The glial cell that forms myelin in the peripheral nervous system.

SCN

See suprachiasmatic nucleus.

SCN9A

See NaV1.7.

scotoma

A region of blindness caused by injury to the visual pathway or brain.

scotopic system

A system in the retina that operates at low levels of light and involves the rods.

SDN-POA

See sexually dimorphic nucleus of the preoptic area.

seasonal affective disorder (SAD)

A depression putatively brought about by the short days of winter.

second messenger

A slow-acting substance in a target cell or postsynaptic cell that amplifies the effects of synaptic or hormonal activity and regulates chemical activity within that cell.

secondary sensory cortex

Also called nonprimary sensory cortex. For a given sensory modality, the cortical regions receiving direct projections from primary sensory cortex for that modality.

secondary sensory ending

Also called flower spray ending. The axon that transmits information from the ends of a muscle spindle.

secondary somatosensory cortex (S2)

Also called somatosensory 2. The region of cortex that receives direct projections from primary somatosensory cortex.

seizure

An epileptic episode.

selective attention

See attention.

selective permeability

The property of a membrane that allows some substances to pass through, but not others.

selective serotonin reuptake inhibitors (SSRIs)

A class of drugs that block the reuptake of transmitter at serotonergic synapses. They are commonly used to treat depression.

semantic memory

Generalized memory— for instance, knowing the meaning of a word without knowing where or when you learned that word.

semantics

The meanings or interpretation of words and sentences in a language.

semen

A mixture of fluids and sperm that is released during ejaculation.

semicircular canal

One of the three fluid-filled tubes in the inner ear that are part of the vestibular system. Each of the tubes, which are at right angles to each other, detects angular acceleration.

senile dementia

A neurological disorder of the aged that is characterized by progressive behavioral deterioration, including personality change and profound intellectual decline. It includes, but is not limited to, Alzheimer’s disease.

senile plaques

Also called amyloid plaques. Small areas of the brain that have abnormal cellular and chemical patterns. Senile plaques correlate with senile dementia.

sensitive period

The period during development in which an organism can be permanently altered by a particular experience or treatment.

sensitization

A process in which the body shows an enhanced response to a given drug after repeated doses.

sensorineural deafness

A hearing impairment that originates from cochlear or auditory nerve lesions.

sensory buffer

An element of the type of memory that stores the very brief sensory impression of a scene.

sensory conflict theory

A theory of motion sickness suggesting that discrepancies between vestibular information and visual information simulate food poisoning and therefore trigger nausea.

sensory nerve

A nerve that conveys sensory information from the periphery into the central nervous system.

sensory neuron

A neuron that is directly affected by changes in the environment, such as light, odor, or touch.

sensory pathway

The chain of neural connections from sensory receptor cells to the cortex.

sensory receptor organ

An organ (such as the eye or ear) specialized to receive particular stimuli.

sensory transduction

The process in which a receptor cell converts the energy in a stimulus into a change in the electrical potential across its membrane.

septal nuclei

A collection of gray matter structures lying medially below the corpus callosum, implicated in the perception of reward.

serotonergic

Referring to neurons that use serotonin as their synaptic transmitter.

serotonin (5-HT)

A synaptic transmitter that is produced in the raphe nuclei and is active in structures throughout the cerebral hemispheres.

serotonin syndrome

Syndrome of confusion, muscle spasms, and fever that may occur when brain levels of serotonin are too high. It is a risk of taking SSRIs.

serotonin-norepinephrine reuptake inhibitor (SNRI)

A drug that blocks the reuptake of transmitter at both serotonergic and noradrenergic synapses.

set point

The point of reference in a feedback system. An example is the setting of a thermostat.

set zone

The range of a variable that a feedback system tries to maintain.

sex determination

The process that initiates either male or female development in an embryo or fetus.

sex steroids

Steroid hormones secreted by the gonads: androgens, estrogens, and progestins.

sexual attraction

The first step in the mating behavior of many animals, in which animals emit stimuli that attract members of the opposite sex.

sexual differentiation

The process by which individuals develop either male-like or female-like bodies and behavior.

sexual dimorphism

The condition in which males and females show pronounced sex differences in appearance.

sexual selection

A form of evolution through natural selection in which members of one sex favor specific heritable traits in the other sex when choosing a reproductive partner.

sexually dimorphic nucleus of the preoptic area (SDN-POA)

A region of the preoptic area that is 5 to 6 times larger in volume in male rats than in females.

sexually receptive

Referring to the state in which an individual (in mammals, typically the female) is willing to copulate.

SFO

See subfornical organ.

shadowing

A task in which the participant is asked to focus attention on one ear or the other while stimuli are being presented separately to both ears.

sham rage

See decorticate rage.

short-term memory (STM)

A form of memory that usually lasts only for seconds, or as long as rehearsal continues, especially while being used during performance of a task.

SIDS

See sudden infant death syndrome.

simple cortical cell

Also called bar detector or edge detector. A cell in the visual cortex that responds best to an edge or a bar that has a particular width, as well as a particular orientation and location in the visual field.

simple partial seizure

Also called absence attack. A seizure that is characterized by a spike-and-wave EEG and often involves a loss of awareness and inability to recall events surrounding the seizure.

simultagnosia

A profound restriction of attention, often limited to a single item or feature.

single-nucleotide polymorphisms

A minor variation within a gene, or neighboring noncoding DNA, where one nucleotide has been substituted for another.

site-directed mutagenesis

A technique in molecular biology that changes the sequence of nucleotides in an existing gene.

skill learning

Learning to perform a task that requires motor coordination.

sleep apnea

A sleep disorder in which respiration slows or stops periodically, waking the person. Excessive daytime sleepiness results from the frequent nocturnal awakening.

sleep cycle

A period of slow-wave sleep followed by a period of REM sleep. In humans, a sleep cycle lasts 90– 110 minutes.

sleep deprivation

The partial or total prevention of sleep.

sleep enuresis

Bed-wetting.

sleep hygiene

Habits, such as avoiding caffeine shortly before bedtime, that promote healthy sleep.

sleep paralysis

A state during the transition to or from sleep, in which the ability to move or talk is temporarily lost.

sleep recovery

The process of sleeping more than is normal, after a period of sleep deprivation, as though in compensation.

sleep spindle

A characteristic 14- to 18-Hz wave in the EEG of a person in stage 2 sleep.

sleep state misperception

Commonly, a person’s perception that he has not been asleep when in fact he has. It typically occurs at the start of a sleep episode.

sleep-maintenance insomnia

Difficulty in staying asleep.

sleep-onset insomnia

Difficulty in falling asleep.

slow-twitch muscle fiber

A type of striated muscle fiber that contracts slowly but does not fatigue readily.

slow-wave sleep (SWS)

Also called NREM 3. A stage of NREM sleep characterized by large-amplitude delta waves (in humans, this is also called stage 3 sleep).

SMA

See supplementary motor area.

smooth muscle

A type of muscle fiber, as in the heart, that is controlled by the autonomic nervous system rather than by voluntary control.

SNB

See spinal nucleus of the bulbocavernosus.

SNRI

See serotonin-norepinephrine reuptake inhibitor.

social neuroscience

The use of neuroscience techniques to understand the neural bases of social processes.

sodium ion (Na⁺)

A sodium atom that carries a positive charge because it has lost one electron.

sodium-potassium pump

The energetically expensive mechanism that pushes sodium ions out of a cell, and potassium ions in.

soma

See cell body.

somatic intervention

An approach to finding relations between body variables and behavioral variables that involves manipulating body structure or function and looking for resultant changes in behavior.

somatic nerve

See spinal nerve.

somatic nervous system

The part of the peripheral nervous system that provides neural connections to the skeletal musculature.

somatomedins

A group of proteins, released from the liver in response to growth hormone, that aid body growth and maintenance.

somatosensory

Referring to body sensation, particularly touch and pain sensation.

somatosensory 1

See primary somatosensory cortex.

somatosensory 2

See secondary somatosensory cortex.

somatotropic hormone

See growth hormone.

somatotropin

See growth hormone.

somnambulism

Sleepwalking.

Southern blot

A method of detecting a particular DNA sequence in the genome of an organism, by separating DNA with gel electrophoresis, blotting the separated DNAs onto nitrocellulose, and then using a nucleotide probe to hybridize with, and highlight, the gene of interest.

spasticity

Markedly increased rigidity in response to forced movement of the limbs.

spatial cognition

Those mental processes that deal with the spatial relationships among objects.

spatial resolution

The ability to observe the detailed structure of the brain.

spatial summation

The summation at the axon hillock of postsynaptic potentials from across the cell body. If this summation reaches threshold, an action potential is triggered.

spatial-frequency filter model

A model of pattern analysis that emphasizes Fourier analysis of visual stimuli.

species

A group of individuals that can readily interbreed to produce fertile offspring.

specific nerve energies

The doctrine that the receptors and neural channels for the different senses are independent and operate in their own special ways and can produce only one particular sensation each.

spectral filtering

Alteration of the amplitude of some, but not all, frequencies in a sound.

spectrally opponent cell

A visual receptor cell that has opposite firing responses to different regions of the spectrum.

sperm

The gamete produced by males for fertilization of eggs (ova).

spinal animal

An animal whose spinal cord has been surgically disconnected from the brain to enable the study of behaviors that do not require brain control.

spinal nerve

Also called somatic nerve. A nerve that emerges from the spinal cord.

spinal nucleus of the bulbocavernosus (SNB)

A group of motor neurons in the spinal cord of rats that innervate striated muscles controlling the penis.

spinocerebellum

The uppermost part of the cerebellum, consisting mostly of the vermis and anterior lobe.

spinothalamic system

See anterolateral system.

split-brain individual

An individual whose corpus callosum has been severed, halting communication between the right and left hemispheres.

SRY gene

A gene on the Y chromosome that directs the developing gonads to become testes. The name SRY stands for sex-determining region on the Y chromosome.

SSRI

See selective serotonin reuptake inhibitor.

stage 1 sleep

Also called NREM 1. The initial stage of NREM sleep, which is characterized by small-amplitude EEG waves of irregular frequency, slow heart rate, and reduced muscle tension.

stage 2 sleep

Also called NREM 2. A stage of NREM sleep that is defined by bursts of regular 14- to 18-Hz EEG waves called sleep spindles.

stage 3 sleep

Also called NREM 3. A stage of NREM sleep that is defined by the presence of large-amplitude, very slow waves (delta waves).

standard condition (SC)

The usual environment for laboratory rodents, with a few animals in a cage and adequate food and water but no complex stimulation.

stapedius

A middle-ear muscle that is attached to the stapes.

stapes

Latin for “ stirrup.” A middle-ear bone that is connected to the oval window.

stem cell

A cell that is undifferentiated and therefore can take on the fate of any cell that a donor organism can produce.

stereocilium

A relatively stiff hair that protrudes from a hair cell in the auditory or vestibular system.

steroid hormones

A class of hormones, each of which is composed of four interconnected rings of carbon atoms.

steroid receptor cofactors

Proteins that affect the cell’s response when a steroid hormone binds its receptor.

stimulus

A physical event that triggers a sensory response.

stimulus cuing

A testing technique in which a cue to the stimulus location is provided before the stimulus itself.

STM

See short-term memory.

stop codon

A trio of nucleotides in DNA to mark the end of transcription.

stress

Any circumstance that upsets homeostatic balance.

stress immunization

The concept that mild stress early in life makes an individual better able to handle stress later in life.

stretch reflex

The contraction of a muscle in response to stretch of that muscle.

stria terminalis

A limbic pathway connecting the amygdala and hypothalamus.

striate cortex

See primary visual cortex.

striated muscle

A type of muscle with a striped appearance, generally under voluntary control.

striatum

The caudate nucleus and putamen together.

stroke

Damage to a region of brain tissue that results from blockage or rupture of vessels that supply blood to that region.

STX

See saxitoxin.

subcoeruleus

A brain region just ventral to the locus coeruleus, associated with REM sleep.

subcutaneous tissue

See hypodermis.

subfornical organ (SFO)

One of the circumventricular organs.

substance abuse

A maladaptive pattern of substance use that has lasted more than a month but does not fully meet the criteria for dependence.

substance P

A peptide transmitter implicated in pain transmission.

substantia nigra

Literally, “ black substance.” A group of pigmented neurons in the midbrain that provides dopaminergic projections to areas of the forebrain, especially the basal ganglia.

subthalamic nucleus

A nucleus just ventral to the thalamus that interacts with the basal ganglia. It is a favored site for deep brain stimulation to treat Parkinson’s disease.

sudden infant death syndrome (SIDS)

Also called crib death. The sudden, unexpected death of an apparently healthy human infant who simply stops breathing, usually during sleep.

sulcus

A furrow of a convoluted brain surface.

superior

In anatomy, pertaining to the higher of two locations. Compare inferior.

superior colliculus (pl. colliculi)

A gray matter structure of the dorsal midbrain that receives visual information and is involved in direction of visual gaze and visual attention to intended stimuli.

superior olivary nuclei

Brainstem nuclei that receive input from both right and left cochlear nuclei and provide the first binaural analysis of auditory information.

supersensitivity psychosis

An exaggerated psychosis that may emerge when doses of antipsychotic medication are reduced, probably as a consequence of the up-regulation of receptors that occurred during drug treatment.

supplementary motor area (SMA)

A region of nonprimary motor cortex that receives input from the basal ganglia and modulates the activity of the primary motor cortex.

suprachiasmatic nucleus (SCN)

A small region of the hypothalamus above the optic chiasm that is the location of a circadian oscillator.

supraoptic nucleus

A hypothalamic nucleus containing neuroendocrine cells that send axons to the posterior pituitary to release oxytocin or vasopressin.

surface dyslexia

Acquired dyslexia in which the person seems to attend only to the fine details of reading.

sustained-attention task

A task in which a single stimulus source or location must be held in the attentional spotlight for a protracted period.

SWS

See slow-wave sleep.

Sylvian fissure

Also called lateral sulcus. A deep fissure that demarcates the temporal lobe.

symbolic cuing task

An attention task in which a symbol indicates to the participant where to voluntarily direct attention in order to detect a stimulus.

sympathetic chain

A chain of ganglia that runs along each side of the spinal column and is part of the sympathetic nervous system.

sympathetic nervous system

A component of the autonomic nervous system that arises from the thoracic and lumbar spinal cord.

synapse rearrangement

Also called synaptic remodeling. The loss of some synapses and the development of others; a refinement of synaptic connections that is often seen in development.

synapse

The tiny gap between neurons where information is passed from one to the other.

synaptic bouton

See axon terminal.

synaptic cleft

The space between the presynaptic and postsynaptic elements.

synaptic delay

The brief delay between the arrival of an action potential at the axon terminal and the creation of a postsynaptic potential.

synaptic remodeling

See synapse rearrangement.

synaptic transmitter

See neurotransmitter.

synaptic vesicle

A small, spherical structure that contains molecules of neurotransmitter.

synaptogenesis

The establishment of synaptic connections as axons and dendrites grow.

synaptotagmin

A specialized protein that responds to calcium ions to trigger vesicular exocytosis.

synergist

A muscle that acts together with another muscle.

synesthesia

A condition in which stimuli in one modality evoke the involuntary experience of an additional sensation in another modality.

syntax

The grammatical rules for constructing phrases and sentences in a language.

syrinx

The vocal organ in birds.

T cell

See T lymphocyte.

T lymphocyte

Also called T cell. An immune system cell, formed in the thymus (hence the T), which includes killer T cells that attack foreign microbes, and helper T cells that secrete cytokines.

T1R

A family of taste receptor proteins that, when particular members heterodimerize, form taste receptors for sweet flavors and umami flavors.

T2R

A family of bitter taste receptors.

TAARs

See trace amine– associated receptors.

tachistoscope test

A test in which stimuli are very briefly exposed in either the left or right visual half field.

tactile

Of or relating to touch.

tardive dyskinesia

A disorder characterized by involuntary movements, especially involving the face, mouth, lips, and tongue. It can be caused by prolonged use of antipsychotic drugs, such as chlorpromazine.

tastant

A substance that can be tasted.

taste bud

A cluster of 50– 150 cells that detects tastes. Taste buds are found in papillae.

taste pore

The small aperture through which tastant molecules are able to access the sensory receptors of the taste bud.

Tau

A protein associated with neurofibrillary tangles in Alzheimer’s disease.

taxonomy

The classification of organisms.

tectorial membrane

A membrane that sits atop the organ of Corti in the cochlear duct.

tectum

The dorsal portion of the midbrain, including the inferior and superior colliculi.

telencephalon

The frontal subdivision of the forebrain that includes the cerebral hemispheres when fully developed.

temporal coding

The encoding of sound frequency in terms of the number of action potentials per second produced by an auditory nerve.

temporal lobe

Large lateral cortical region of each cerebral hemisphere, continuous with the parietal lobe posteriorly and separated from the frontal lobe by the Sylvian fissure.

temporal resolution

The ability of an imaging technique to track changes in the brain over time.

temporal summation

The summation of postsynaptic potentials that reach the axon hillock at different times. The closer in time the potentials occur, the more complete the summation.

temporoparietal junction (TPJ)

The point in the brain where the temporal and parietal lobes meet that plays a role in shifting attention to a new location after target onset.

tendon

Strong tissue that connects muscle to bone.

tensor tympani

The muscle attached to the malleus that modulates mechanical linkage to protect the delicate receptor cells of the inner ear from damaging sounds.

testes

The male gonads, which produce sperm and androgenic steroid hormones.

testosterone

A hormone, produced by male gonads, that controls a variety of bodily changes that become visible at puberty.

tetanus

An intense volley of action potentials.

tetanus toxin

A toxin that cleaves SNAREs, disabling neurotransmitter release.

tetrodotoxin (TTX)

A toxin from puffer fish ovaries that blocks the voltage-gated sodium channel, preventing action potential conduction.

thalamus

The brain regions surrounding the third ventricle at the top of the brainstem that trade information with the cortex.

THC

See δ9-tetrahydrocannabinol.

thermogenin

Also called UCP1. A specialized protein that allows mitochondria to turn energy directly into heat.

thermoregulation

The active process of closely regulating body temperature around a set value.

third ventricle

The midline ventricle that conducts cerebrospinal fluid from the lateral ventricle to the fourth ventricle.

thoracic

Referring to the 12 spinal segments below the cervical (neck) portion of the spinal cord, corresponding to the chest.

threshold

The stimulus intensity that is just adequate to trigger an action potential.

thyroid gland

An endocrine gland, located in the throat, that regulates cellular metabolism throughout the body.

thyroid hormones

Two hormones, triiodothyronine and thyroxine (also called tetraiodothyronine), released from the thyroid gland that have widespread effects, including growth and maintenance of the brain.

thyroid-stimulating hormone (TSH)

A tropic hormone, released by the anterior pituitary gland, that signals the thyroid gland to secrete its hormones.

thyrotropin-releasing hormone (TRH)

A hypothalamic hormone that regulates the release of thyroid-stimulating hormone from the anterior pituitary.

timbre

The characteristic sound quality of a musical instrument, as determined by the relative intensities of its various harmonics.

tinnitus

A sensation of noises or ringing in the ears.

tip link

A fine, threadlike fiber that runs along and connects the tips of stereocilia.

TMS

See transcranial magnetic stimulation.

tolerance

A condition in which, with repeated exposure to a drug, an individual becomes less responsive to a constant dose.

tonic receptor

A receptor in which the frequency of action potentials declines slowly or not at all as stimulation is maintained.

tonic-clonic seizure

Also called grand mal seizure. A type of generalized epileptic seizure in which nerve cells fire in high-frequency bursts.

tonotopic organization

A major organizational feature in auditory systems in which neurons are arranged as an orderly map of stimulus frequency, with cells responsive to high frequencies located at a distance from those responsive to low frequencies.

top-down attention

See voluntary attention.

top-down process

A process in which higher-order cognitive processes control lower-order systems, often reflecting conscious control.

Tourette’s syndrome

A heightened sensitivity to tactile, auditory, and visual stimuli that may be accompanied by the buildup of an urge to emit verbal or phonic tics.

TPJ

See temporoparietal junction.

trace amine– associated receptors (TAARs)

A family of probable pheromone receptors produced by neurons in the main olfactory epithelium.

tract

A bundle of axons found within the central nervous system.

tract tracer

A compound used to identify the routes and interconnections of neuronal projections.

transcranial magnetic stimulation (TMS)

Localized, noninvasive stimulation of cortical neurons through the application of strong magnetic fields.

transcript

The mRNA strand that is produced when a stretch of DNA is “ read.”

transcription factor

A substance that binds to recognition sites on DNA and alters the rate of expression of particular genes.

transcription

The process during which mRNA forms bases complementary to a strand of DNA. The resulting message (called a transcript) is then used to translate the DNA code into protein molecules.

transduction

The conversion of one form of energy to another.

transgenic

Referring to an animal in which a new or altered gene has been deliberately introduced into the genome.

transient receptor potential type M3 (TRPM3)

A receptor, found in some free nerve endings, that opens its channel in response to rising temperatures.

transient receptor potential vanilloid type 1 (TRPV1)

Also called vanilloid receptor 1. A receptor that binds capsaicin to transmit the burning sensation from chili peppers and normally detects sudden increases in temperature.

translation

The process by which amino acids are linked together (directed by an mRNA molecule) to form protein molecules.

transmitter

See neurotransmitter.

transmitter reuptake

The reabsorption of synaptic transmitter by the axon terminal from which it was released.

transporter

Specialized receptor in the presynaptic membrane that recognizes transmitter molecules and returns them to the presynaptic neuron for reuse.

transverse plane

See coronal plane.

treble

An aspect of pitch corresponding to the subjective experience of high-frequency sounds (especially musical sounds, such as cymbals).

TRH

See thyrotropin-releasing hormone.

trichromatic hypothesis

A hypothesis of color perception stating that there are three different types of cones, each excited by a different region of the spectrum and each having a separate pathway to the brain.

tricyclics or tricyclic antidepressants

A class of drugs that act by increasing the synaptic accumulation of serotonin and norepinephrine.

trigeminal nerve

Cranial nerve V, which receives information from the face and controlling jaw musculature.

trinucleotide repeat

Repetition of the same three nucleotides within a gene, which can lead to dysfunction, as in the cases of Huntington’s disease and fragile X syndrome.

trophic factor

See neurotrophic factor.

tropic hormones

A class of anterior pituitary hormones that affect the secretion of other endocrine glands.

TRPM3

See transient receptor potential type M3.

TRPM8

See cool-menthol receptor 1.

TRPV1

See transient receptor potential vanilloid type 1.

TSH

See thyroid-stimulating hormone.

t-SNARE

Specialized protein anchored to the presynaptic “ target” membrane to bind v-SNAREs to dock vesicles, making them ready for release.

TTX

See tetrodotoxin.

tuberomammillary nucleus

A region of the basal hypothalamus, near the pituitary stalk, that plays a role in generating SWS.

tuning curve

A graph of the responses of a single auditory nerve fiber or neuron to sounds that vary in frequency and intensity.

Turner’s syndrome

A condition seen in individuals carrying a single X chromosome but no other sex chromosome.

two-photon excitation microscopy

Method of providing many low-energy photons that can penetrate deep into tissues, such that the simultaneous arrival of two photons at a fluorescent molecule is sufficient to elicit a visible photon in response.

tympanic canal

See scala tympani.

tympanic membrane

Also called eardrum. The partition between the external ear and the middle ear.

typical antipsychotics

Also called typical neuroleptics. A major class of antischizophrenic drugs that share an antagonist activity at dopamine D2 receptors.

UCP1

See thermogenin.

ultradian

Referring to a rhythmic biological event whose period is shorter than that of a circadian rhythm, usually from several minutes to several hours long.

ultrasound

High-frequency sound, generally above the threshold for human hearing, at about 20,000 Hz.

umami

One of the five basic tastes (along with salty, sour, sweet, and bitter), probably mediated by amino acids in foods.

unipolar neuron

Also called monopolar neuron. A nerve cell with a single branch that leaves the cell body and then extends in two directions: one end is the receptive pole, the other end the output zone.

up-regulation

A compensatory increase in receptor availability at the synapses of a neuron.

utricle

A small, fluid-filled sac in the vestibular system above the saccule that responds to static positions of the head.

V1

See primary visual cortex.

vaccination

Injection of a foreign substance, such as deactivated viruses or conjugated molecules of drugs of abuse like cocaine, in order to provoke the production of antibodies against the foreign substance.

vagus nerve

Cranial nerve X, which regulates the viscera (organs) and transmits signals from the viscera to the brain.

vanilloid receptor 1

See transient receptor potential vanilloid type 1.

varicosity

The axonal swelling from which neurotransmitter diffuses in a nondirected synapse.

ventral

In anatomy, toward the belly or front of the body, or the bottom of the brain. Compare dorsal.

ventral root

The branch of a spinal nerve, arising from the ventral horn of the spinal cord, that carries motor messages from the spinal cord to the peripheral nervous system.

ventral tegmental area (VTA)

A portion of the midbrain that projects dopaminergic fibers to the nucleus accumbens.

ventricular system

A system of fluid-filled cavities inside the brain.

ventricular zone

Also called ependymal layer. A region lining the cerebral ventricles that displays mitosis, providing neurons early in development and glial cells throughout life.

ventromedial hypothalamus (VMH)

A hypothalamic region involved in eating, sexual, and aggressive behaviors.

vertebral arteries

Arteries that ascend the vertebrae, enter the base of the skull, and join together to form the basilar artery.

vertex spike

A sharp-wave EEG pattern that is seen during stage 1 slow-wave sleep.

vestibular canal

See scala vestibuli.

vestibular nuclei

Brainstem nuclei that receive information from the vestibular organs through cranial nerve VIII (the vestibulocochlear nerve).

vestibular system

The inner ear system that encodes the orientation and acceleration of the head in three axes, crucial for the sense of balance.

vestibulocerebellum

The middle portion of the cerebellum, sandwiched between the spinocerebellum and the cerebrocerebellum and consisting of the nodule and the flocculus.

vestibulocochlear nerve

Cranial nerve VIII, which runs from the cochlea to the brainstem auditory nuclei.

vestibulo-ocular reflex (VOR)

The brainstem mechanism that maintains gaze on a visual object despite movements of the head.

visual acuity

Sharpness of vision.

visual field

The whole area that you can see without moving your head or eyes.

visual P1 effect

An increase in amplitude of the P1 component of event-related potentials that occurs for stimuli that are the focus of attention.

vitamin A aldehyde

See retinal.

VMH

See ventromedial hypothalamus.

VNO

See vomeronasal organ.

voltage clamping

The use of electrodes to inject current into an axon or neuron to keep the membrane potential at a set value. The apparatus measures how much current must be injected to counteract any ion channel openings.

voltage-gated Na⁺ channel

A Na⁺-selective channel that opens or closes in response to changes in the voltage of the local membrane potential and mediates the action potential.

voluntary attention

Also called consciously or endogenously controlled attention or top-down attention. The voluntary direction of attention toward specific aspects of the environment, in accordance with our interests and goals.

vomeronasal organ (VNO)

A collection of specialized receptor cells, near to but separate from the olfactory epithelium, that detect pheromones and send electrical signals to the accessory olfactory bulb in the brain.

vomeronasal system

A specialized chemical detection system that detects pheromones and transmits information to the brain.

VOR

See vestibulo-ocular reflex.

v-SNARE

Specialized protein anchored to vesicles to aid their fusing to the presynaptic membrane to release neurotransmitter.

VTA

See ventral tegmental area.

Wada test

A test in which a short-lasting anesthetic is delivered into one carotid artery to determine which cerebral hemisphere principally mediates language.

Wallerian degeneration

See anterograde degeneration.

wavelength

The length between two peaks in a repeated stimulus such as a wave, light, or sound.

Wernicke’s aphasia

See fluent aphasia.

Wernicke’s area

A region of temporoparietal cortex in the brain that is involved in the perception and production of speech.

Western blot

A method of detecting a particular protein molecule in a tissue or organ, by separating proteins from that source with gel electrophoresis, blotting the separated proteins onto nitrocellulose, and then using an antibody that binds, and highlights, the protein of interest.

white matter

A pale-colored layer underneath the cortex that consists largely of axons with white myelin sheaths.

Williams syndrome

A disorder characterized by fluent linguistic function but poor performance on standard IQ tests and great difficulty with spatial processing.

withdrawal symptom

An uncomfortable symptom that arises when a person stops taking a drug that he or she has used frequently, especially at high doses.

wolffian ducts

A duct system in the embryo that will develop into male structures (the epididymis, vas deferens, and seminal vesicles) if testes are present.

word deafness

The specific inability to hear words, although other sounds can be detected.

working memory

A type of short-term memory that holds information available for ready access during performance of a task.

zeitgeber

Literally, “ time giver” (in German). The stimulus (usually the light-dark cycle) that entrains circadian rhythms.

zygote

The fertilized egg.