Intracranial EEG Correlates of Expectancy and Memory Formation in the Human Hippocampus and Nucleus Accumbens

Nikolai Axmacher, Michael X. Cohen, Juergen Fell, Sven Haupt, Matthias Dümpelmann, Christian E. Elger, Thomas E. Schlaepfer, Doris Lenartz, Volker Sturm, Charan Ranganath

Research output: Contribution to journalArticlepeer-review

108 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)541-549
Number of pages9
Issue number4
StatePublished - Feb 25 2010
Externally publishedYes



ASJC Scopus subject areas

  • Neuroscience(all)


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