Pontine reticular formation neurons: relationship of discharge to motor activity

Abstract

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.

Fig. 1.

Relationship of PRF unit discharge to motor activity. (A) Polygraphic display of unit firing in unrestrained cat. Unit discharge is accompanied by phasic EMG activity. (Inset) High speed oscilloscopic tracing from same record (arrow) demonstrating the absence of artifact in the microwire recording. This unit had an average signal-to-noise ratio. (B) Unit responses to strong shock stimuli were brief, most discharge being time-locked to movements (augmented EMG) occurring during stimulation rather than to the shock stimulus itself. Dots indicate time of delivery of 1-msec shock stimulus to receptive field. (Inset) Brief response time-locked to shock in microwire recording of same unit. (C) Two units with different spontaneous activity levels simultaneously recorded during head restraint. Augmented unit discharge was correlated with muscle contraction. (D) During grooming, unit dischaiged rhythmically, with bursts time-locked to movements. Head motion created the slow rhythmic artifact in this broad-spectrum EMG recording. Grooming had been in progress for 20 minutes and continued for an additional 5 minutes. Abbreviations: EMG, electromyogram of dorsal neck muscles; Unit, the pulse output of a window discriminator. (A) and (D) are from the same cell. The 10-seconds marker applies to all four panels, exclusive of the two insets.