Reinforcing concomitants of electrically elicited vocalizations.

In 38 squirrel monkeys 251 vocalization-producing electrode positions were tested for their positive and negative reinforcing properties. Two groups of vocalization-producing brain areas could be distinguished: One group in which the electrically elicited vocalization was independent of the accompanying reinforcement effect, and a second group in which vocalization and reinforcement effect were correlated. The first group included the anterior cingulate gyrus, the adjacent supplementary motor area, gyrus rectus, ventromedial edge of the capsula interna, caudal periaqueductal gray and adjacent parabrachial region. The second group consited of the caudatum, septum, substantia innominata, amygdala, inferior thalamic peduncle, stria terminalis, midline thalamus, ventral and periventricular hypothalamus, substantia nigra, rostral periaqueductal gray, dorsolateral midbrain tegmentum and lateral medulla. It is hypothesized that the first group contains predominantly or exclusively "primary" vocalization substrates; the second group is thought to be composed mainly of structures whose stimulation yields vocalization secondarily due to stimulus induced motivational changes.