State-dependent respiratory depression elicited by stimulation of the orbital frontal cortex

The effect of electrical stimulation of the orbital frontal cortex on respiration was studied in unanesthetized, freely moving cats across sleep-waking states. Single trains of forty 300-microA, 0.5-ms, constant-current pulses at 60 Hz were delivered to the orbital frontal cortex at four points in the respiratory cycle. Stimuli delivered during expiration produced an immediate switch to inspiration. Stimuli delivered during inspiration reduced inspiratory EMG slope and peak EMG amplitude, and prolonged inspiration. Stimuli delivered during early inspiration produced greater effects than stimuli delivered during late inspiration. Stimulation effects were elicited during quiet waking and quiet sleep but not during rapid-eye-movement sleep. These results suggest that the orbital frontal cortex may contribute to respiratory phase switching, and that its influence on brain stem structures is attenuated during rapid-eye-movement sleep.