Chapter 9 Summary

Declarative memory is conscious memory for events (episodic memory) and facts (semantic memory). Episodic memory may involve remembering contextual details (recollection) or merely having vague feelings of knowing (familiarity).
According to the most popular model of declarative memory, during encoding, memory traces are stored in the cortical regions that process each type of information; at the same time, the hippocampus stores indices pointing to these cortical locations. During this period of storage, some memories are strengthened (by consolidation) while others are lost. During retrieval, activation of hippocampal index representations leads to the reactivation of cortical traces. Damage to the hippocampus prevents access to cortical memory traces, producing memory loss (amnesia). Importantly, the hippocampus is no longer needed after memories have been consolidated, explaining why amnesia patients like H.M. can often remember remote memories. Prefrontal and parietal regions are assumed to mediate control processes during both encoding and retrieval.
Hippocampal memory representations have been described as spatial, relational, or episodic. Developmental and adult amnesia cases suggest that the hippocampus is more critical for episodic than for semantic memory. Conversely, semantic dementia cases indicate that the anterior temporal lobe is more critical for semantic than for episodic memory. The hippocampus has also been more strongly linked to recollection than to familiarity.
According to a three-process model, the perirhinal cortex is concerned with memory for objects; the parahippocampal cortex, with memory for spatial layouts; and the hippocampus, with domain-general relational memory.
The organization of semantic knowledge may reflect the sensory and functional properties of objects and/or semantic categories. Semantic dementia cases suggest that the anterior temporal lobes could be an amodal semantic “hub,” with some links to social knowledge.
Functional neuroimaging studies and single-unit recordings show that regions activated during encoding tend to be reactivated during retrieval. Consistent with transfer-appropriate processing, this reactivation varies with specific encoding strategies.
The left inferior frontal gyrus has been associated with successful episodic encoding, possibly because of its role in semantic processing. The left middle frontal gyrus has been associated with organizing information during encoding and during retrieval. The right dorsolateral prefrontal cortex has been linked to monitoring processes; and the frontopolar cortex, to retrieval mode.
Posterior lateral parietal regions are often activated in episodic retrieval. Dorsal parietal activations have been linked to top-down attention; and ventral parietal activations, to bottom-up attention. During encoding, ventral parietal activations are associated with subsequent forgetting.
Encoding is not completed immediately, but requires a process of synaptic consolidation, involving gene expression, protein synthesis, and synaptic plasticity.
System consolidation is the formation of direct connections among cortical traces, which allows these traces to be accessed independently of the hippocampus and could explain why remote memories are often spared by hippocampal damage. According to a multiple-trace theory, the sparing of remote memories reflects the creation of new hippocampal traces each time a memory is reactivated.
Consolidation is promoted by memory reactivation, whether by intentional practice, during slow-wave sleep, or at rest.