Contextually Mediated Spontaneous Retrieval Is Specific to the Hippocampus.
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.
Department of Psychology, University of Oregon, Eugene, OR 97403, USA. Electronic address: niclong@uoregon.edu.
Nicole M
NM
Long
Department of Neurology, Thomas Jefferson University Hospital, Philadelphia, PA 19107, USA.
Michael R
MR
Sperling
Department of Neurology, Mayo Clinic, Rochester, MN 55905, USA.
Gregory A
GA
Worrell
Department of Neurology, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA.
Kathryn A
KA
Davis
Department of Neurosurgery, Emory University Hospital, Atlanta, GA 30322, USA.
Robert E
RE
Gross
Department of Neurosurgery, University of Texas Southwestern, Dallas, TX 75390, USA.
Bradley C
BC
Lega
Department of Neurology, Dartmouth Medical Center, Lebanon, NH 03756, USA.
Barbara C
BC
Jobst
Department of Neurosurgery, Columbia University Medical Center, New York, NY 10032, USA.
Sameer A
SA
Sheth
Surgical Neurology Branch, National Institutes of Health, Bethesda, MD 20814, USA.
Kareem
K
Zaghloul
Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA.
Joel M
JM
Stein
Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: kahana@psych.upenn.edu.
Michael J
MJ
Kahana
D000293:Adolescent; D000328:Adult; D004569:Electroencephalography; D004827:Epilepsy / Q000503:physiopathology; D005260:Female; D006624:Hippocampus / Q000502:physiology*; D006801:Humans; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D008875:Middle Aged; D055815:Young Adult
context; episodic memory; free recall; iEEG; retrieval