Neurons in the human medial temporal lobe track multiple temporal contexts during episodic memory processing

Hye Bin Yoo, Gray Umbach, Bradley Lega

Research output: Contribution to journalArticlepeer-review

Abstract

Episodic memory requires associating items with temporal context, a process for which the medial temporal lobe (MTL) is critical. This study uses recordings from 27 human subjects who were undergoing surgical intervention for intractable epilepsy. These same data were also utilized in Umbach et al. (2020). We identify 103 memory-sensitive neurons in the hippocampus and entorhinal cortex, whose firing rates predicted successful episodic memory encoding as subjects performed a verbal free recall task. These neurons exhibit important properties. First, as predicted from the temporal context model, they demonstrate reinstatement of firing patterns observed during encoding at the time of retrieval. The magnitude of reinstatement predicted the tendency of subjects to cluster retrieved memory items according to input serial position. Also, we found that spiking activity of these neurons was locked to the phase of hippocampal theta oscillations, but that the mean phase of spiking shifted between memory encoding versus retrieval. This unique observation is consistent with predictions of the “Separate Phases at Encoding And Retrieval (SPEAR)” model. Together, the properties we identify for memory-sensitive neurons characterize direct electrophysiological mechanisms for the representation of contextual information in the human MTL.

Original languageEnglish (US)
Article number118689
JournalNeuroImage
Volume245
DOIs
StatePublished - Dec 15 2021

Keywords

  • Episodic memory
  • Local field potential
  • MTL
  • Phase offset
  • Single unit
  • Temporal clustering

ASJC Scopus subject areas

  • Neurology
  • Cognitive Neuroscience

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