Projections from the cortical larynx area in the squirrel monkey.

The projections from the cortical vocal fold area were studied in five squirrel monkeys (Saimiri sciureus) with the aid of the autoradiographic tracing technique. The location of the cortical vocal fold area was determined by exploring the exposed frontal cortex with roving electrodes while examining the larynx for vocal fold adduction. The following projections were found: To the orbital cortex (area 11), dorsomedial frontal cortex (areas 6 and 8), Broca's area (area 44), lower fronto-parietal cortex (areas 6, 4, 3 and 1), fronto-parietal operculum (area 50), insula (areas 14 and 13), caudatum, putamen, claustrum nucl. reticularis th., nucl. ventralis anterior, nucl. ventralis lateralis, nucl. ventralis posteromedialis, nucl. centralis inferior, nucl. centralis lateralis, nucl. medialis dorsalis, nucl. pulvinaris medialis, griseum pontis, nucl. parabrachialis medialis and lateralis, nucl. tr. spinalis n. trigemini and nucl. tr. solitarri. A comparison of the projection system with a previous mapping study for vocalization (Jürgens and Ploog, 1970) revealed that there are two areas yielding vocalization when electrically stimulated which receive direct projections from the cortical larynx area, namely, the cortex around the anterior sulcus cinguli and the parabrachial nuclei at the pons-midbrain transition. The possible relevance of these structures for vocalization is discussed.