Fast Gamma Rhythms in the Hippocampus Promote Encoding of Novel Object-Place Pairings

eNeuro. 2016 May 12;3(2):ENEURO.0001-16.2016. doi: 10.1523/ENEURO.0001-16.2016. eCollection 2016 Mar-Apr.

Abstract

Hippocampal gamma rhythms increase during mnemonic operations (Johnson and Redish, 2007; Montgomery and Buzsáki, 2007; Sederberg et al., 2007; Jutras et al., 2009; Trimper et al., 2014) and may affect memory encoding by coordinating activity of neurons that code related information (Jensen and Lisman, 2005). Here, a hippocampal-dependent, object-place association task (Clark et al., 2000; Broadbent et al., 2004; Eacott and Norman, 2004; Lee et al., 2005; Winters et al., 2008; Barker and Warburton, 2011) was used in rats to investigate how slow and fast gamma rhythms in the hippocampus relate to encoding of memories for novel object-place associations. In novel object tasks, the degree of hippocampal dependence has been reported to vary depending on the type of novelty (Eichenbaum et al., 2007; Winters et al., 2008). Therefore, gamma activity was examined during three novelty conditions: a novel object presented in a location where a familiar object had been (NO), a familiar object presented in a location where no object had been (NL), and a novel object presented in a location where no object had been (NO+NL). The strongest and most consistent effects were observed for fast gamma rhythms during the NO+NL condition. Fast gamma power, CA3-CA1 phase synchrony, and phase-locking of place cell spikes increased during exploration of novel, compared to familiar, object-place associations. Additionally, place cell spiking during exploration of novel object-place pairings was increased when fast gamma rhythms were present. These results suggest that fast gamma rhythms promote encoding of memories for novel object-place associations.

Keywords: CA1; gamma oscillations; gamma rhythms; hippocampus; memory; place cells.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Action Potentials / physiology
  • Analysis of Variance
  • Animals
  • Association Learning / physiology*
  • Discrimination, Psychological / physiology
  • Exploratory Behavior
  • Gamma Rhythm / physiology*
  • Hippocampus / cytology*
  • Hippocampus / physiology
  • Locomotion / physiology
  • Male
  • Nerve Net / physiology
  • Place Cells / physiology
  • Rats
  • Rats, Long-Evans
  • Recognition, Psychology / physiology*
  • Spectrum Analysis