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A cortical–hippocampal system for declarative memory

Abstract

Recent neurobiological studies have begun to reveal the cognitive and neural coding mechanisms that underlie declarative memory — our ability to recollect everyday events and factual knowledge. These studies indicate that the critical circuitry involves bidirectional connections between the neocortex, the parahippocampal region and the hippocampus. Each of these areas makes a unique contribution to memory processing. Widespread high-order neocortical areas provide dedicated processors for perceptual, motor or cognitive information that is influenced by other components of the system. The parahippocampal region mediates convergence of this information and extends the persistence of neocortical memory representations. The hippocampus encodes the sequences of places and events that compose episodic memories, and links them together through their common elements. Here I describe how these mechanisms work together to create and re-create fully networked representations of previous experiences and knowledge about the world.

Key Points

  • Neuropsychological and experimental lesion studies indicate that the hippocampus plays a critical role between initial formation of memories and their final storage in the brain.

  • Neocortical association areas and the parahippocampal region play different roles in declarative memory as shown by electrophysiological recordings and the results of experimental lesions on various memory tests.

  • Neocortical areas play a role in the perceptual and cognitive demands of memory tests and can mediate short-term memory.

  • The parahippocampal region is involved in extending the persistence of memory for single stimuli for short periods of time in the absence of interference and for the maintenance of information concerning stimulus familiarity for longer periods in the face of interference.

  • The hippocampus encodes the sequences of places and events that constitute episodic memory and links them together in an organization that underlies the ability to make inferential associations across different experiences.

  • Interactions between the various components of the system are critical and may underlie the eventual storage of declarative memories in neocortical areas of the brain.

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Figure 1: The anatomy of the hippocampal memory system.
Figure 2: Firing patterns associated with memory performance in ideal cortical neurons.
Figure 3: Performance of rats with hippocampal damage in the Morris water maze.
Figure 4: The social transmission of food preferences task.
Figure 5: Hippocampal neuronal firing patterns in rats during an odour DNMS task.
Figure 6: Place cell firing patterns associated with performance in a spatial memory task on a T-maze87.

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Acknowledgements

This work was funded by grants from the NIMH and the NIA.

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FURTHER INFORMATION

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ENCYCLOPEDIA OF LIFE SCIENCES

Learning and memory

Amnesia

Neural activity and the development of brain circuits

Neural networks and behaviour

Long-term potentiation

Protein phosphorylation and long-term synaptic plasticity

Glossary

EPISODIC REPRESENTATIONS

Neural firing patterns, which encode the sequence of events that compose a unique, personal experience.

SEMANTIC KNOWLEDGE

An organization of factual information independent of the specific episodes in which that information was acquired.

PROCEDURAL MEMORY

The representation of a series of actions or perceptual processing functions that occur unconsciously, and typically result in increased speed or accuracy with repetitions.

EMOTIONAL MEMORY

The representation of a positive or negative affect associated with specific stimuli. Typically not subject to conscious recollection but reflected in attraction, avoidance or autonomic nervous system activation.

WORKING MEMORY

The representation of items held in consciousness during experiences or after retrieval of memories. Short-lasting and associated with active rehearsal or manipulation of information.

PRIMING

The facilitation of recognition, reproduction or biases in selection of stimuli that have recently been perceived.

SPATIAL LEARNING

Acquisition of information about spatial relations among objects in the environment, typically reflected in the ability to navigate through the environment using new routes.

PLACE CELLS

Hippocampal principal cells that fire selectively when an animal is in a particular location in its environment.

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Eichenbaum, H. A cortical–hippocampal system for declarative memory. Nat Rev Neurosci 1, 41–50 (2000). https://doi.org/10.1038/35036213

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