Gamma Oscillations and Their Cross-frequency Coupling in the Primate Hippocampus during Sleep

Abstract

Study Objectives:

The mechanism by which sleep consolidates memory is unclear. Based on the two-stage model of memory consolidation, different functions for slow wave sleep (SWS) and rapid eye movement (REM) sleep have been proposed; thus, state-dependent changes of neural oscillations in the hippocampus might clarify this fundamental question.

Methods:

We recorded hippocampal local field potentials from freely behaving monkeys via telemetry and analyzed their nonstationary oscillations using Hilbert-Huang transform.

Results:

By applying a recently developed empirical mode decomposition analysis, we found strong cross-frequency coupling between high-frequency and slow wave oscillations during SWS and a prominent increase of gamma band activity in short bursts during REM sleep in unanesthetized primates' hippocampus.

Conclusion:

Spatiotemporal integration through coupled oscillations during slow wave sleep might be a physiological basis of system consolidation, whereas gamma bursts during rapid eye movement sleep might be related to synaptic consolidation in the local hippocampal neural circuit.

cross-frequency coupling, Hilbert-Huang transform, hippocampus, monkey, REM sleep