Concept cells: the building blocks of declarative memory functions

Abstract

Intracranial recordings in subjects suffering from intractable epilepsy — made during their evaluation for an eventual surgical removal of the epileptic focus — have allowed the extraordinary opportunity to study the firing of multiple single neurons in awake and behaving human subjects. These studies have shown that neurons in the human medial temporal lobe respond in a remarkably selective and abstract manner to particular persons or objects, such as Jennifer Aniston, Luke Skywalker or the Tower of Pisa. These neurons have been named 'Jennifer Aniston neurons' or, more recently, 'concept cells'. I argue that the sparse, explicit and abstract representation of these neurons is crucial for memory functions, such as the creation of associations and the transition between related concepts that leads to episodic memories and the flow of consciousness.

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Figure 1: Visual perception and memory pathway.
Figure 2: Example of a neuron with multimodal invariance.
Figure 3: Example of all-or-none responses with conscious perception.
Figure 4: Hierarchical processing in the human medial temporal lobe.
Figure 5: Sparse representation of concepts in the medial temporal lobe.

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Acknowledgements

The author is indebted to his collaborators, C. Koch and I. Fried, all the researchers in their laboratories and his laboratory that have contributed to the recording and analysis of these data, and the patients for their willingness to participate in these studies.

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Borges and Memory: Encounters with the Human Brain

Glossary

Attractor

A state or set of states towards which neighbouring states converge. In neuroscience, percepts and memories are thought to act as attractors of neuronal representations.

Cell assembly

A network of functionally connected neurons that is activated by a specific mental process (for example, a visual stimulus or the retrieval of a memory).

Combinatorial explosion

A problem in which the number of possibilities increases exponentially. A combinatorial explosion argument has been raised to disprove the possibility of grandmother cells, as there are not enough neurons in the brain to encode all possible concepts and their instances (for example, grandmother smiling, grandmother drinking tea, grandmother wearing a red pullover, and so on).

Declarative memory

Also known as explicit memory, this is the memory of things that can be named and consciously recalled things that one can be explicitly aware of.

Episodic memory

A form of declarative memory that involves personally experienced events and situations.

Grandmother cell

A neural representation in which relatively few neurons encode for only one thing. Grandmother cell coding is the extreme version of sparse coding.

Grid cells

Neurons in the rodent entorhinal cortex that fire when the animal is at one of several specific locations in an environment and that are organized in a grid-like manner.

Lateral processing

Recurrent processing within a given brain area.

Medial temporal lobe

(MTL). A system of anatomically connected structures that is critical for declarative memory. It comprises the hippocampus, amygdala and the entorhinal, parahippocampal and perirhinal cortices.

Non-topographic organization

A representation in which nearby neurons represent disparate things. It contrasts with a topographic organization, in which nearby neurons encode similar stimulus features or motor outputs (and connect to nearby neurons in other areas).

Oddball task

A task in which subjects have to detect an infrequent deviant stimulus (the oddball or target) that is randomly placed in a sequence of frequent non-target stimuli.

Pattern completion

The process by which a whole-cell assembly is activated from partial inputs.

Semantic memory

A form of declarative memory that involves the memory of facts and knowledge about the world.

Theta phase precession

A phenomenon in which place cells fire at increasingly earlier phases of the underlying theta oscillation when approaching the place field.

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Quiroga, R. Concept cells: the building blocks of declarative memory functions. Nat Rev Neurosci 13, 587–597 (2012). https://doi.org/10.1038/nrn3251

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