Sharp wave ripples during visual exploration in the primate hippocampus

Timothy K. Leonard, Jonathan M. Mikkila, Emad N. Eskandar, Jason L. Gerrard, Daniel Kaping, Shaun R. Patel, Thilo Womelsdorf, Kari L. Hoffman

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


Hippocampal sharp-wave ripples (SWRs) are highly synchronous oscillatory field potentials that are thought to facilitate memory consolidation. SWRs typically occur during quiescent states, when neural activity reflecting recent experience is replayed. In rodents, SWRs also occur during brief locomotor pauses in maze exploration, where they appear to support learning during experience. In this study, we detected SWRs that occurred during quiescent states, but also during goal-directed visual exploration in nonhuman primates (Macaca mulatta). The exploratory SWRs showed peak frequency bands similar to those of quiescent SWRs, and both types were inhibited at the onset of their respective behavioral epochs. In apparent contrast to rodent SWRs, these exploratory SWRs occurred during active periods of exploration, e.g., while animals searched for a target object in a scene. SWRs were associated with smaller saccades and longer fixations. Also, when they coincided with target-object fixations during search, detection was more likely than when these events were decoupled. Although we observed high gamma-band field potentials of similar frequency to SWRs, only the SWRs accompanied greater spiking synchrony in neural populations. These results reveal that SWRs are not limited to off-line states as conventionally defined; rather, they occur during active and informative performance windows. The exploratory SWR in primates is an infrequent occurrence associated with active, attentive performance, which may indicate a new, extended role of SWRs during exploration in primates.

Original languageEnglish (US)
Pages (from-to)14771-14782
Number of pages12
JournalJournal of Neuroscience
Issue number44
StatePublished - Nov 4 2015
Externally publishedYes


  • Change detection
  • Macaque
  • Natural scenes
  • Search
  • Sleep
  • Theta

ASJC Scopus subject areas

  • General Neuroscience


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