title: Intracranial EEG correlates of expectancy and memory formation in the human hippocampus and nucleus accumbens.
abstract: The human brain is adept at anticipating upcoming events, but in a rapidly changing world, it is essential to detect and encode events that violate these expectancies. Unexpected events are more likely to be remembered than predictable events, but the underlying neural mechanisms for these effects remain unclear. We report intracranial EEG recordings from the hippocampus of epilepsy patients, and from the nucleus accumbens of depression patients. We found that unexpected stimuli enhance an early (187 ms) and a late (482 ms) hippocampal potential, and that the late potential is associated with successful memory encoding for these stimuli. Recordings from the nucleus accumbens revealed a late potential (peak at 475 ms), which increases in magnitude during unexpected items, but no subsequent memory effect and no early component. These results are consistent with the hypothesis that activity in a loop involving the hippocampus and the nucleus accumbens promotes encoding of unexpected events.
authors.affiliation: Department of Epileptology, University of Bonn, 53105 Bonn, Germany. nikolai.axmacher@ukb.uni-bonn.de <nikolai.axmacher@ukb.uni-bonn.de>
authors.forename: Nikolai
authors.initials: N
authors.lastname: Axmacher
authors.forename: Michael X
authors.initials: MX
authors.lastname: Cohen
authors.forename: Juergen
authors.initials: J
authors.lastname: Fell
authors.forename: Sven
authors.initials: S
authors.lastname: Haupt
authors.forename: Matthias
authors.initials: M
authors.lastname: Dümpelmann
authors.forename: Christian E
authors.initials: CE
authors.lastname: Elger
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Schlaepfer
authors.forename: Doris
authors.initials: D
authors.lastname: Lenartz
authors.forename: Volker
authors.initials: V
authors.lastname: Sturm
authors.forename: Charan
authors.initials: C
authors.lastname: Ranganath
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D003463:Cues; D003866:Depressive Disorder / Q000503:physiopathology; D004569:Electroencephalography; D004827:Epilepsy / Q000503:physiopathology; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006624:Hippocampus / Q000502:physiology*; D006801:Humans; D008297:Male; D008568:Memory / Q000502:physiology*; D008875:Middle Aged; D009415:Nerve Net / Q000502:physiology; D009483:Neuropsychological Tests; D009714:Nucleus Accumbens / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D021641:Recognition, Psychology / Q000502:physiology; D012153:Retention, Psychology / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors