Contextually Mediated Spontaneous Retrieval Is Specific to the Hippocampus

• Type of Material: Article
• Authors: Nicole Long, University of Oregon; Michael Sperling, Thomas Jefferson University Hospital; Gregory A. Worrell, Mayo Clinic; Kathryn A. Davis, Hospital of the University of Pennsylvania; Robert Gross, Emory University; Bradley C. Lega, University of Texas Southwestern; Barbara C. Jobst, Dartmouth Medical School; Sameer A. Sheth, Columbia University; Kareem Zaghloul, National Institute of Health; Joel M. Stein, Hospital of the University of Pennsylvania; Michael J. Kahana, University of Pennsylvania
• Language: English
• Date: 2017-04-03
• Publisher: Elsevier (Cell Press)
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2017 Elsevier Ltd
• Final Published Version (URL): http://dx.doi.org/10.1016/j.cub.2017.02.054
• Title of Journal or Parent Work: Current Biology
• ISSN: 0960-9822
• Volume: 27
• Issue: 7
• Start Page: 1074
• End Page: 1079
• Grant/Funding Information: 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: HIGH-FREQUENCY ACTIVITY; PARIETAL CORTEX; FALSE MEMORIES; Science & Technology; EPISODIC MEMORY; ACTIVITY PATTERNS; DORSOLATERAL PREFRONTAL CORTEX; Cell Biology; Life Sciences & Biomedicine; WORKING-MEMORY; Biochemistry & Molecular Biology; TEMPORAL-LOBE; FREE-RECALL; SUBSEQUENT MEMORY
• Research Categories: Biology, Neuroscience; Biology, Molecular; Chemistry, Biochemistry

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.