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Author Notes:

Nicole M. Long, Department of Psychology, University of Oregon, Eugene, OR 97403, USA, niclong@uoregon.edu.

N.M.L. and M.J.K. designed experiments.

N.M.L. analyzed the data.

J.M.S. localized the electrodes.

M.R.S., G.A.W., K.A.D., R.E.G., B.C.L., B.C.J., S.A.S., and K.Z. recruited participants and provided general assistance.

N.M.L. and M.J.K. wrote the manuscript.

All authors provided feedback on the manuscript.

M.J.K. supervised the research.

We thank Blackrock Microsystems for providing neural recording equipment.

We are indebted to all patients who have selflessly volunteered their time to participate in our study.

The views, opinions, and/or findings contained in this material are those of the authors and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.

Subjects:

Research Funding:

This work was supported by the DARPA Restoring Active Memory program (Cooperative Agreement N66001-14-2-4032) and National Institutes of Health grant MH55687.

Keywords:

  • Science & Technology
  • Life Sciences & Biomedicine
  • Biochemistry & Molecular Biology
  • Cell Biology
  • DORSOLATERAL PREFRONTAL CORTEX
  • HIGH-FREQUENCY ACTIVITY
  • FREE-RECALL
  • EPISODIC MEMORY
  • FALSE MEMORIES
  • TEMPORAL-LOBE
  • SUBSEQUENT MEMORY
  • ACTIVITY PATTERNS
  • PARIETAL CORTEX
  • WORKING-MEMORY

Contextually Mediated Spontaneous Retrieval Is Specific to the Hippocampus

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Journal Title:

Current Biology

Volume:

Volume 27, Number 7

Publisher:

, Pages 1074-1079

Type of Work:

Article | Post-print: After Peer Review

Abstract:

Although it is now well established that the hippocampus supports memory encoding [1, 2], little is known about hippocampal activity during spontaneous memory retrieval. Recent intracranial electroencephalographic (iEEG) work has shown that hippocampal activity during encoding predicts subsequent temporal organization of memories [3] , supporting a role in contextual binding. It is an open question, however, whether the hippocampus similarly supports contextually mediated processes during retrieval. Here, we analyzed iEEG recordings obtained from 215 epilepsy patients as they performed a free recall task. To identify neural activity specifically associated with contextual retrieval, we compared correct recalls, intrusions (incorrect recall of either items from prior lists or items not previously studied), and deliberations (matched periods during recall when no items came to mind). Neural signals that differentiate correct recalls from both other retrieval classes reflect contextual retrieval, as correct recalls alone arise from the correct context. We found that in the hippocampus, high-frequency activity (HFA, 44–100 Hz), a proxy for neural activation [4], was greater prior to correct recalls relative to the other retrieval classes, with no differentiation between intrusions and deliberations. This pattern was not observed in other memory-related cortical regions, including DLPFC, thus supporting a specific hippocampal contribution to contextually mediated memory retrieval.

Copyright information:

© 2017 Elsevier Ltd

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