Primate phonation: unilateral and bilateral cingulate lesion effects.

Four juvenile Macaca mulatta were trained on a multiple schedule to perform discriminative vocalization and lever press tasks. Sequential unilateral and bilateral lesions of the anterior cingulate gyrus were made with testing of vocalization and lever press at each stage. Performance of the two behavioral tasks was assessed in terms of total responses, latency, efficiency and error index. Unilateral damage had a profound effect on vocal performance in one monkey. There was a significant deficit in total vocal responses and an increase of vocal response latency. No such impairment occurred from equivalent damage in the 3 remaining animals, despite comparable lesions. None of the 4 suffered changes in discriminative lever press following unilateral lesions. The second lesion (producing bilateral damage) had little further effect on the animal that exhibited an initial deficit from a unilateral insult. In contrast, this step in the remaining monkeys produced latency and total vocal response scores that approximated the scores obtained from the monkey with a single, unilateral hemisphere lesion. The evidence indicates there is lateral asymmetry in vocal mechanisms involving anterior cingulate cortex. This may be related to the hemisphere controlling the preferred hand. The principal effect of anterior cingulate damage involves impaired response initiation.