Convergent projections of different limbic vocalization areas in the squirrel monkey

The projections of four different sub-areas within the anterior limbic cortex, all yielding vocalization when electrically stimulated, were compared in six squirrel monkeys by the autoradiographic tracing technique. Areas of convergence of the projections from all four vocalization loci were the cortex within the anterior cingulate sulcus, a zone following the inferior thalamic peduncle from the central amygdaloid nucleus through the substantia innominata into the midline thalamus, a second zone following the periventricular fibre system from the anterior diencephalon to the caudal midbrain and dorsolateral pontine tegmentum and, finally, the tail of the caudate nucleus. Except for the latter, all of these brain structures produce vocalization when electrically stimulated. The call types elicitable from these projection areas are sometimes different from those elicitable from the anterior limbic cortex. It is hypothesized that the anterior limbic cortex controls vocalization directly, independently of the specific motivational state underlying it.