The reactivity of the somesthetic S1 cortex during sleep and waking in the rat.

The reactivity of the somesthetic S1 cortex was studied in the rat, in the course of the seven principle stages of the sleep-waking cycle, in terms of the variation in amplitude of positive wave 4 of the evoked potential induced by stimulation of the thalamocortical radiations. The amplitude of positive wave 4 is minimal during waking with theta (attentive and/or active). It increases in the course of waking without theta, to reach its maximum during the stage of sleep with slow waves. The amplitude decreases with the deepening of slow sleep (spindles, intermediate stage) to a level near to waking without theta, during rapid sleep. No significant difference is observed during periods of eye movements bursts. The variability of the amplitude of intra-state responses is lowest in the phases of waking and paradoxical sleep. The recovery cycle of the S1 cortex responses is long (several hundreds of milliseconds). The rate of recovery is inversely proportional to the amplitude of the response to the conditioning stimulus. It is therefore higher during waking and rapid sleep than during the different stages of slow sleep. These results are integrated in the neurophysiological data of sleep in the rat.