Hippocampus
Volume 18, Issue 5 , Pages 519 - 529
Transient 23-30 Hz oscillations in mouse hippocampus during
exploration of novel environments
Joshua D. Berke 1 2 *, Vaughn Hetrick 1, Jason Breck 1, Robert W.
Greene 3 4
1Department of Psychology, University of Michigan, Ann Arbor, Michigan
2Program in Neuroscience, University of Michigan, Ann Arbor, Michigan
3Department of Psychiatry, University of Texas Southwestern, Dallas,
Texas
4Department of Psychiatry, Dallas VAMC, Dallas, Texas
email: Joshua D. Berke (jdberke@[EMAIL PROTECTED]
)
*Correspondence to Joshua D. Berke, Department of Psychology,
University of Michigan, Ann Arbor, MI 48104, USA
Abstract
The hippocampus is a key brain structure for the encoding of new
experiences and environments. Hippocampal activity shows distinct
oscillatory patterns, but the relation****ps between oscillations and
memory are not well understood. Here we describe bursts of hippocampal
23-30 Hz (beta2) oscillations in mice exploring novel, but not
familiar, environments. In marked contrast to the relatively invariant
8 Hz theta rhythm, beta2 power was weak during the very first lap of
the novel environment, increased sharply as the mice reencountered
their start point, then persisted for only a few minutes. Novelty-
evoked oscillations reflected precise synchronization of individual
neurons, and participating pyramidal cells showed a selective
enhancement of spatial specificity. Through focal viral manipulations,
we found that novelty-evoked oscillations required functional NMDA
receptors in CA3, a subregion critical for fast oscillations in vitro.
These findings suggest that beta2 oscillations indicate a hippocampal
dynamic state that facilitates the formation of unique contextual
representations.
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