Prof. John Wixted
Distinguished Professor of Psychology
University of California, San DiegoThe 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.