There are indications that in the therapsid-mammalian transition changes in the auditory and vocal apparatus afforded audiovocal communication as a means of maintaining maternal-offspring contact and contact of members of a group. The just completed present project is part of an investigation concerned with identifying the cerebral representation of the separation call, a basic mammalian vocalization that serves the above noted functions. For this purpose, squirrel monkeys are tested for their ability to produce spontaneous calls in isolation before and after ablations of different parts of the brain. The present study has focused on the midline frontolimbic cortex, one of two cortical areas where stimulation elicits vocalization in monkeys. Evidence derived by the process of elimination indicates that the spontaneous calls depend on the concerted action of a continuous band of rostal limbic cortex comprising parts of areas 24, 25, and 12. Ablation of the midline frontal neocortex peripheral to this limbic zone is compatible with criterion performance in the production of the call. The present report also includes ancillary observations in regard to separation calls emitted while the subject is awakening from sodium pentobarbital (Nembutal) anesthesia, as well as following the intraventricular administration of oxytocin.
