Power and coherence of cortical High Frequency Oscillations during wakefulness and sleep

Abstract

Recently, a novel type of fast cortical oscillatory activity that occurs between 110 and 160 Hz (high-frequency oscillations (HFO)) was described. HFO are modulated by the theta rhythm in hippocampus and neocortex during active wakefulness and REM sleep. Since theta-HFO coupling increases during REM, a role for HFO in memory consolidation has been proposed. However, global properties like the cortex-wide topographic distribution, and the cortico-cortical coherence remain unknown.

In the present study, we recorded the electroencephalogram during sleep and wakefulness in the rat, and analyzed the spatial extent of the HFO band power and coherence.

We confirmed that the HFO amplitude is phase-locked to theta oscillations and is modified by behavioral states. During active wakefulness, HFO power was relatively higher in the neocortex and olfactory bulb compared to sleep. HFO power decreased during non-REM and had an intermediate level during REM sleep. Furthermore, coherence was larger during active wakefulness than non-REM, while REM showed a complex pattern in which coherence increased only in intra and decrease in inter-hemispheric combination of electrodes. This coherence pattern is different from gamma (30-100 Hz) coherence, which is reduced during REM sleep.

The present data show an important HFO cortico-cortical dialogue during active wakefulness even when the level of theta co-modulation is lower than in REM. In contrast, during REM, this dialogue is highly modulated by theta, and restricted to intra-hemispheric medial-posterior cortical regions. Further studies combining behavior, electrophysiology and new analytical tools are needed to plunge deeper into the functional significance of the HFO.

This article is protected by copyright. All rights reserved.

http://ift.tt/2xKXy9R