Power and coherence in the EEG of the rat: impact of behavioral states, cortical area, lateralization and light/dark phases

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. Thalamo-cortical activity can be examined by means of the 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), as well as in motor, somatosensory and visual neocortical areas. We also analyzed the laterality (right Vs. left hemispheres) of the signals, as well as the iEEG in function 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 were 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, while we did not find right/left differences in power either in W or sleep, we observed that during REM sleep intra-hemispheric coherence differs between both hemispheres. We conclude that the iEEG dynamics is highly dependent on the cortical area and behavioral states. We also determine that there are light/dark phases disparities in the iEEG that emerge during sleep, and that intra-hemispheric connectivity differs between both hemispheres only during REM sleep.