The relationship of periaqueductal gray neurons to vocalization and laryngeal EMG in the behaving monkey.

The midbrain periaqueductal gray (PAG) of most higher animals has been shown by stimulation and lesion methods to be important in vocalization. In order to learn how the PAG is involved in vocalization, activity from single PAG neurons was recorded from 3 awake, vocalizing monkeys. From a population of 149 units that were temporally related to vocalization, 91 were analyzed with respect to specific parameters of vocalization and laryngeal EMG activity. Measures of the activity of 52 units were significantly correlated with vocalization or EMG activity. Units tended to be correlated with only a few measures of vocalization or EMG activity suggesting rather specific relationships between PAG units and vocalization measures. Microstimulation near recorded cells usually did not excite every muscle sampled, suggesting PAG projections to brainstem motor nuclei may be somewhat specific. The results confirm previous suggestions that the PAG may be involved in the coordination of brainstem motor nuclei during vocalization.