Effects of hypnogenic vagal stimulation on thalamic neuronal activity in cats.

Neuronal responses from the ventro-postero-medial (VPM) and reticular (NR) nuclei of cat thalamus to vagal stimulation was recorded during wakefulness (W), slow-wave-sleep (SWS), and paradoxical sleep (PS) using chronically implanted microelectrodes. Cellular firing was facilitated in NR and depressed in VPM when weak, hyponogenic stimuli were delivered to the vagal nerve during W and SWS. Higher intensity vagal stimulation increased firing frequency and duration of discharge in both nuclei. Vagally induced discharges of several VPM neurons were depressed by NR stimulation. We speculate that intrathalamic mechanisms play a role in the genesis of induced synchronization and sleep.