title: Theta and high-frequency activity mark spontaneous recall of episodic memories.
abstract: Humans possess the remarkable ability to search their memory, allowing specific past episodes to be re-experienced spontaneously. Here, we administered a free recall test to 114 neurosurgical patients and used intracranial theta and high-frequency activity (HFA) to identify the spatiotemporal pattern of neural activity underlying spontaneous episodic retrieval. We found that retrieval evolved in three electrophysiological stages composed of: (1) early theta oscillations in the right temporal cortex, (2) increased HFA in the left hemisphere including the medial temporal lobe (MTL), left inferior frontal gyrus, as well as the ventrolateral temporal cortex, and (3) motor/language activation during vocalization of the retrieved item. Of these responses, increased HFA in the left MTL predicted recall performance. These results suggest that spontaneous recall of verbal episodic memories involves a spatiotemporal pattern of spectral changes across the brain; however, high-frequency activity in the left MTL represents a final common pathway of episodic retrieval.
authors.affiliation: Neuroscience Graduate Group.
authors.forename: John F
authors.initials: JF
authors.lastname: Burke
authors.affiliation: Departments of Neurological Surgery, and.
authors.forename: Ashwini D
authors.initials: AD
authors.lastname: Sharan
authors.affiliation: Neurology, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania 19107.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Sperling
authors.affiliation: Neuroscience Graduate Group.
authors.forename: Ashwin G
authors.initials: AG
authors.lastname: Ramayya
authors.affiliation: Departments of Neurological Surgery, and.
authors.forename: James J
authors.initials: JJ
authors.lastname: Evans
authors.affiliation: Departments of Psychology.
authors.forename: M Karl
authors.initials: MK
authors.lastname: Healey
authors.affiliation: Departments of Psychology.
authors.forename: Erin N
authors.initials: EN
authors.lastname: Beck
authors.affiliation: Neurology, and.
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Davis
authors.affiliation: Neurosurgery, University of Pennsylvania, Philadelphia, Pennsylvania 19104, and.
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Lucas
authors.affiliation: Departments of Psychology, kahana@sas.upenn.edu.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Kahana
mesh_terms: D001931:Brain Mapping; D002540:Cerebral Cortex / Q000503:physiopathology*; D004569:Electroencephalography; D004827:Epilepsy / Q000473:pathology / Q000601:surgery; D005260:Female; D007839:Functional Laterality; D065818:Gamma Rhythm / Q000502:physiology*; D006801:Humans; D007802:Language; D008137:Longitudinal Studies; D008297:Male; D061212:Memory, Episodic; D011939:Mental Recall / Q000502:physiology*; D009483:Neuropsychological Tests; D010775:Photic Stimulation; D013057:Spectrum Analysis; D013826:Theta Rhythm / Q000502:physiology*; D013997:Time Factors; D014706:Verbal Learning
keywords: ECoG; episodic retrieval; high-frequency activity; memory; theta