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Curr Biol. 2019 Apr 1;29(7):1100-1111.e4. doi: 10.1016/j.cub.2019.02.020. Epub 2019 Mar 21.

Dynamic Theta Networks in the Human Medial Temporal Lobe Support Episodic Memory.

Author information

1
Department of Bioengineering, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: esolo@pennmedicine.upenn.edu.
2
Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA.
3
Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, PA 19107, USA.
4
Department of Neurology, Thomas Jefferson University Hospital, Philadelphia, PA 19107, USA.
5
Department of Neurology, Department of Physiology and Bioengineering, Mayo Clinic, Rochester, MN 55905, USA.
6
Department of Neurosurgery, Emory School of Medicine, Atlanta, GA 30322, USA.
7
Department of Neurosurgery, University of Texas Southwestern, Dallas, TX 75390, USA.
8
Department of Neurology, Dartmouth Medical Center, Lebanon, NH 03756, USA.
9
Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104, USA.
10
Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: kahana@psych.upenn.edu.

Abstract

The medial temporal lobe (MTL) is a locus of episodic memory in the human brain. It is comprised of cytologically distinct subregions that, in concert, give rise to successful encoding and retrieval of context-dependent memories. However, the functional connections between these subregions are poorly understood. To determine functional connectivity among MTL subregions, we had 131 subjects fitted with indwelling electrodes perform a verbal memory task and asked how encoding or retrieval correlated with inter-regional synchronization. Using phase-based measures of connectivity, we found that synchronous theta (4-8 Hz) activity underlies successful episodic memory. During encoding, we observed a dynamic pattern of connections converging on the left entorhinal cortex, beginning with the perirhinal cortex and shifting through hippocampal subfields. Retrieval-associated networks demonstrated enhanced involvement of the subiculum and CA1, reflecting a substantial reorganization of the encoding network. We posit that coherent theta activity within the MTL marks periods of successful memory, but distinct patterns of connectivity dissociate key stages of memory processing.

KEYWORDS:

ECoG; LFP; connectivity; entorhinal cortex; episodic memory; hippocampus; networks; theta

PMID:
30905609
PMCID:
PMC6445741
[Available on 2020-04-01]
DOI:
10.1016/j.cub.2019.02.020

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