Pontine reticular formation neurons: relationship of discharge to motor activity.

The discharge correlates of pontine reticular formation units were investigated in unrestrained cats. In agreement with previous investigations using immobilized preparations, we found that these cells had high rates of activity in rapid eye movement sleep, and responded in waking to somatic, auditory, and vestibular stimuli at short latencies, many having polysensory responses and exhibiting rapid "habituation." However, despite the sensory responses of these cells, most unit activity could not be explained by the presence of sensory stimuli. Intense firing occurred in association with specific movements. Units deprived of their adequate somatic, vestibular, and auditory stimuli showed undiminished discharge rates during motor activity. Discrete sensory stimuli evoked sustained unit firing only when they also evoked a motor response. We conclude that activity in pontine reticular formation neurons is more closely related to motor output than to sensory input.