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Chronic experiments were performed on four cats to study evoked spike activity in neurons in the oral nucleus of the pons to electrical stimulation of the posterior hypothalamus in the waking, slow-wave sleep, and paradoxical sleep states. A total of 42% of study neurons were found to respond to stimulation during waking. PS-on and PS-off neurons were identified in the oral nucleus of the pons, along with phasic cells showing bursts of activity during the physical manifestations of paradoxical sleep. Stimulation induced inhibitory responses in PS-on neurons, excitatory responses in PS-off neurons, and excitatory and inhibitory responses in 68% and 32% respectively of phasic neurons. The magnitudes of evoked responses in these neurons changed during the sleep-waking cycle. These data demonstrate the involvement of the posterior hypothalamus in controlling the mechanisms of paradoxical sleep, these mechanisms being located in the oral nucleus of the pons.