Hippocampal pattern completion is linked to gamma power increases and alpha power decreases during recollection

Research output: Contribution to journalArticlepeer-review


  • Sebastian Michelmann
  • Mathilde Bonnefond
  • Nikolai Axmacher
  • Juergen Fell

External organisations

  • Ruhr-Universität Bochum
  • University of Bonn, Bonn, Germany.
  • Radboud Universiteit


How do we retrieve vivid memories upon encountering a simple cue? Computational models suggest that this feat is accomplished by pattern completion processes involving the hippocampus. However, empirical evidence for hippocampal pattern completion and its underlying mechanisms has remained elusive. Here, we recorded direct intracranial EEG as human participants performed an associative memory task. For each study (encoding) and test (retrieval) event, we derived time-frequency resolved representational patterns in the hippocampus and compared the extent of pattern reinstatement for different mnemonic outcomes. Results show that successful associative recognition (AR) yields enhanced event-specific reinstatement of encoding patterns compared to non-associative item recognition (IR). Moreover, we found that gamma power (50–90 Hz) increases – in conjunction with alpha power (8–12 Hz) decreases not only distinguish AR from IR, but also correlate with the level of hippocampal reinstatement. These results link single-shot hippocampal pattern completion to episodic recollection and reveal how oscillatory dynamics in the gamma and alpha bands orchestrate these mnemonic processes.


Original languageEnglish
Article numbere17397
Number of pages18
Publication statusPublished - 10 Aug 2016


  • episodic memory, hippocampus, intracranial EEG, neural oscillations, pattern completion