Afferent subcortical connections into the motor cortical larynx area in the rhesus monkey.

In three rhesus monkeys (Macaca mulatta), the inferior motor cortex was explored by electrical stimulation for sites yielding vocal fold adduction. The retrograde tracer wheat germ-agglutinin-conjugated horseradish peroxidase was injected into the effective sites. Within the forebrain, retrogradely labeled cells were found in the claustrum, basal nucleus of Meynert, substantia innominata, extended amygdala, lateral and posterior hypothalamic area, field H of Forel, and a number of thalamic nuclei with the strongest labeling in the nuclei ventralis lateralis, ventralis posteromedialis, including its parvocellular part, medialis dorsalis and centrum medianum, and weaker labeling in the nuclei ventralis anterior, ventralis posterolateralis, intermediodorsalis, paracentralis, parafascicularis and pulvinaris anterior. In the midbrain, labeling was found in the deep mesencephalic nucleus, ventral tegmental area, and substantia nigra. In the lower brainstem, labeled cells were found in the pontine reticular formation, median and dorsal raphe nuclei, medial parabrachial nucleus, and locus coeruleus. The findings are discussed in terms of the possible role of these structures in voluntary vocal control.