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Chapter Summary
This chapter introduces the theoretical approaches and practical methodologies common to the field of cognitive neuroscience. Cognitive neuroscience is an interdisciplinary field dedicated to the study of brain mechanisms and of the human mental functions that are intimately associated with these brain mechanisms (modules). Originally theorists such as Gall and Spurzheim attempted to map specific mental functions to specific locations of the brain. This localization of function approach has its roots in phrenology—the “science” of divining personality traits from the physical features of the skull. Later theorists such as Franz and his students, using an approach called “ablation,” demonstrated that the amount of brain tissue remaining after ablation was more important than the location of the ablation. Their approach—rooted in the laws of mass action and equipotentiality—maintained that mental processes result from of the brain as a whole and not from individual parts.
Due to its equal consideration of both mental functions and brain functions, cognitive neuroscience does not limit itself to studying the human brain as a mere organ, and thus often finds itself at the crossroads of the seemingly unresolvable philosophical debate over how mind and brain relate. Descartes’ interactionism theory maintains that the mind and brain are separate, although they interact with each other, and each can influence the other. Another view is Huxley’s concept of epiphenomenalism, which postulated that the mind is merely a by-product of the brain, and thus only the brain has any causal influence. Fechner, on the other hand, supported the idea of parallelism, whereby the mind and the brain are simply two aspects of a single reality. Finally, isomorphism, which is related to Gestalt psychology, extends the claims of parallelism further in claiming that internal representations and the underlying brain processes are inherently organized into patterns, and that these patterns in the mind and brain are similar in all their structural traits.
There are several methods that researchers used and still use today in order to conduct their inquiries or support their theories. A popular although limited way to explore human processes and behaviours is the use of animal research. Many approaches to studying the brain, such as experimental brain lesioning, can be conducted only using animal models. The use of animal models raises a number of considerations, and researchers are held to high ethical standards. Much of what we know of the micro-organization of brain structure is attributed to animal studies. A second way to examine brain functions is to conduct behavioural studies in humans. Researchers can either study healthy participants or individuals with pre-existing brain injuries. Although no single case of brain injury provides definitive results, studying large numbers of individuals can lead to important breakthroughs in the understanding of brain functioning (e.g., Broca’s and Wernicke’s areas and other aphasias). Similarly, surgical intervention can also be insightful (e.g., Sperry’s Nobel Prize–winning work using split brain studies). Another research method consists of placing electrodes on the scalp and measuring the electrical signals emitted in response to a stimulus (event-related potential). Position emission tomography (PET) can also be used to determine which areas of the brain are active during select tasks. However, because it requires subjects to be exposed to radioactive sub-stances, PET has recently been replaced with functional magnetic resonance imagery (fMRI), which measures changes in blood oxygen levels with the aid of a large magnetic field and has been used to make assumptions on cortical activity. A recent application of fMRI is called diffusion tensor imagining (DTI), which allows researchers to visualize white-matter tracts in the brain. Magnetoencephalography (MEG) measures the magnetic fields produced by electrical activity in the brain, and therefore provides an enhanced temporal resolution when compared with fMRI, although, the spatial resolution is still superior in fMRI. None of these methods tells the whole story of what the brain is doing and when it is doing it, but they do provide a useful aid in understanding human brain functioning. In addition to the methods that measure brain activity, other approaches, such as connectionism, aim to model mental functions based on brain-like neural networks. While no approach alone is capable of providing researchers with a complete understanding of the mind’s processes, combining approaches has enabled a more complete understanding of behaviour and function.
Chapter Objectives
- To examine the key issues in the localization of function debate.
- To outline the theoretical issues surrounding the relationship between the mind and the brain.
- To explain approaches to studying that relationship.
- To identify the advantages and limitations of the various methods used to localize cognitive processes in the brain.