Coding of Episodic Memory in the Human Hippocampus
Neurocomputational models have long posited that episodic memories in the human hippocampus are represented by sparse, stimulus-specific neural codes. A concomitant proposal is that when sparse-distributed neural assemblies become active, they suppress the activity of competing neurons (neural sharpening). We investigated episodic memory coding in the hippocampus and amygdala by measuring single-neuron responses from 20 epilepsy patients (12 female) undergoing intracranial monitoring while they completed a continuous recognition memory task. In the left hippocampus, the distribution of single-neuron activity indicated that only a small fraction of neurons exhibited strong responding to a given repeated word and that each repeated word elicited strong responding in a different small fraction of neurons. This finding reflects sparse distributed coding. The remaining large fraction of neurons exhibited a concurrent reduction in firing rates relative to novel words. The observed pattern accords with longstanding predictions that have previously received scant support from single-cell recordings from human hippocampus.
Medical Subject Headings
Proceedings of the National Academy of Sciences of the United States of America
Digital Object Identifier (DOI)
Wixted, John T.; Goldinger, Stephen D.; Squire, Larry R.; Kuhn, Joel R.; Papesh, Megan H.; Smith, Kris A.; Treiman, David M.; and Steinmetz, Peter N., "Coding of Episodic Memory in the Human Hippocampus" (2018). Neurology. 259.