Role of the periaqueductal grey in vocal expression of emotion.

In 32 squirrel monkeys (Saimiri sciureus) the role of the periaqueductal grey has been investigated by combined stimulation/lesioning and by neuroanatomical experiments. The results are as follows. Firstly, periaqueductal lesions invading the laterally adjacent tegmentum abolish species-specific calls elicitable by electrical brain stimulation. This holds for stimulation sites rostral as well as caudal to this area. The only vocalizations which survive are phonations of an artificial character which can be evoked from the lateral medulla. Spontaneous vocalizations also seem to be abolished. Secondly, vocalizations elicited from the periaqueductal grey are not affected by bilateral lesions in vocalization-eliciting areas rostral to it, but are abolished by lesions in the dorsolateral pons and ventrolateral medulla. Thirdly, the periaqueductal grey receives direct projections from all vocalization-eliciting areas tested, viz. the precallosal cingulate gyrus, gyrus rectus, medial amygdata, central amygdaloid nucleus/substantia innominata, nucleus striae terminalis, dorsal hypothalamus, midline thalamus, periventricular grey, dorsolateral and ventrolateral midbrain tegmentum. Fourthly, the periaqueductal grey projects directly to the nucleus ambiguus, the site of the laryngeal motoneurones. The course of the main bulk of fibres corresponds to the lesion sites effective in abolishing periaqueductally elicited vocalizations. From these results, it was concluded that the caudal periaqueductal-lateral tegmental area is a necessary relay station for all external and internal stimuli capable of inducing species-specific calls. Its position within the stimulus-response loop seems to be on the output side, immediately above the level of motor-corrdination but below that of stimulus recognition.