Power and Coherence in the EEG of the Rat: Impact of Behavioral States, Cortical Area, Lateralization and Light/Dark Phases.

Alejandra Mondino,Matías Cavelli,Lucía Osorio,Pablo Torterolo,Alicia Costa,Giancarlo Vanini,Joaquín González,Santiago Castro-Zaballa

doi:10.3390/clockssleep2040039

Abstract

The sleep-wake cycle is constituted by three behavioral states: wakefulness (W), non-REM (NREM) and REM sleep. These states are associated with drastic changes in cognitive capacities, mostly determined by the function of the thalamo-cortical system, whose activity can be examined by means of intra-cranial electroencephalogram (iEEG). With the purpose to study in depth the basal activity of the iEEG in adult rats, we analyzed the spectral power and coherence of the iEEG during W and sleep in the paleocortex (olfactory bulb), and in neocortical areas. We also analyzed the laterality of the signals, as well as the influence of the light and dark phases. We found that the iEEG power and coherence of the whole spectrum were largely affected by behavioral states and highly dependent on the cortical areas recorded. We also determined that there are night/day differences in power and coherence during sleep, but not in W. Finally, we observed that, during REM sleep, intra-hemispheric coherence differs between right and left hemispheres. We conclude that the iEEG dynamics are highly dependent on the cortical area and behavioral states. Moreover, there are light/dark phases disparities in the iEEG during sleep, and intra-hemispheric connectivity differs between both hemispheres during REM sleep.

Highlights

The brain is a complex system, in which parallel processing coexists with serial operations within highly interconnected networks, but without a single coordinating center
The sleep–wake cycle is a critical physiological process and one of the most preserved biological rhythms through evolution [6]. This cycle is composed of wakefulness (W), non-rapid eye movement (NREM) and rapid eye movement (REM) sleep states, that are distinguished by their behavior and electrophysiological signatures, which can be captured by intra-cranial electroencephalogram (iEEG) signals [3,7]
We studied the influence of the cortical site, employing electrodes located on the olfactory bulb (OB), frontal, parietal and occipital cortex, as well as the impact of laterality and the influence of dark and light phases

Summary

Introduction

The brain is a complex system, in which parallel processing coexists with serial operations within highly interconnected networks, but without a single coordinating center. The sleep–wake cycle is a critical physiological process and one of the most preserved biological rhythms through evolution [6] This cycle is composed of wakefulness (W), non-rapid eye movement (NREM) and rapid eye movement (REM) sleep states, that are distinguished by their behavior and electrophysiological signatures, which can be captured by iEEG signals [3,7]. Accompanying these electro-cortical differences among states, the cognitive capacities drastically change during the cycle. Consciousness is lost during deep NREM sleep, and emerges in an altered fashion during REM sleep, when most vivid dreams occur [3,8]

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