Anterograde Projections of the Motorcortical Tongue Area in the Saddle-Back Tamarin (Saguinus fuscicollis)

Abstract

In the New World monkey Saguinus fuscicollis, the anterograde projections of the motorcortical tongue area were studied. Three animals were analyzed. In two, biotin dextran amine was used as tracer; in the third, Phaseolus vulgaris leucoagglutinin was used. Identification of the tongue area was carried out by electrical brain stimulation. Intracortical projections were found into the neighboring primary motor cortex, ventral premotor cortex, frontoopercular cortex, and primary and secondary somatosensory cortex. Projections also ended in the ventrolateral prefrontal cortex, orbital cortex, supplementary motor area, anterior cingulate cortex and agranular as well as granular insula. In addition, weaker labeling was found in the inferior and dorsal parietal cortex, and perirhinal and inferotemporal cortex. Subcortically, there was a heavy projection into the ventral putamen, a moderate projection into the caudate nucleus and claustrum, and a weak projection into the anterior, central and lateral amygdala. In the thalamus, terminal labeling was found in the nuclei ventralis posterior medialis, ventralis lateralis, reticularis, centralis lateralis, medialis dorsalis, pulvinaris oralis, centrum medianum, reuniens and suprageniculatus in an order of intensity. Subthalamically, weak projections could be traced into the zona incerta and lateral hypothalamus. In the midbrain, labeling was found in the deep layers of the colliculus superior, area praetectalis, dorsal reticular formation and, very sparsely, in the periaqueductal gray. In the lower brainstem, fibers ended in the griseum pontis, medial and lateral parabrachial nuclei, lateral pontine and medullary reticular formation, paramedian and dorsal reticular nuclei, solitary tract nucleus and principal as well as spinal trigeminal nuclei. No terminals were found in the hypoglossal nucleus itself; there were, however, terminals in the immediately bordering reticular formation.