Several sleep studies have shown that the excitability of the sensorimotor system is reduced in sleep as compared with wakefulness (W), although the mechanisms underlying the reduction of excitability across the sleep-wake cycle are still unclear. We recently reported reduction in the excitability of the jaw-opening reflex evoked by low-intensity intra-oral electrical stimulation during quiet sleep (QS) in monkeys (Lavigne et al. SfN Abst 618.15, 2003), and the aim of this study was to determine if there are also differences between W and QS in the excitability of corticobulbar projections producing rhythmic jaw movements (RJM). RJM were evoked by intracortical microstimulation (ICMS; 3s train, 150 x 0.2 ms pulses, 333 Hz) applied by a microelectrode to the monkey’s cortical masticatory area (CMA). The monkey (macaca fascicularis; 4.1 kg) was trained to sleep in a primate chair, in a sound-attenuated and dark room. Sleep was recorded and scored with standard criteria and commercial software. The physiologi...