The Representation of Episodic Memory in Single Neurons of the Human Hippocampus - John Wixted

Prof. John Wixted

Distinguished Professor of Psychology

University of California, San Diego

The Representation of Episodic Memory in Single Neurons of the Human Hippocampus The hippocampus is known to play a fundamental role in episodic memory, but it is not known how mnemonic information is coded by the activity of individual hippocampal neurons. Three different coding schemes have been considered: a localist coding scheme, a fully distributed coding scheme, and a sparse distributed coding scheme. Sparse distributed coding has long been hypothesized to be the most efficient way for hippocampal neurons to rapidly encode pattern-separated episodic memories without overwriting previously stored information. We investigated the representation of episodic memory in 9 epilepsy patients undergoing intracranial monitoring as they discriminated between 32 recently studied words (targets) and 32 new words (foils). We found that single-unit activity was higher in response to targets compared to foils. Further, for each neuron, only one or two of the 32 targets elicited a strong response, and different neurons were activated by different targets. These findings support the idea that episodic memory is supported by a sparse distributed neural code.