The thalamic projection of hypoglossal afferents in the rhesus monkey

Abstract

The present experiments were designed to determine the location within the thalamus of the hypoglossal nerve afferent projection. Electrolytic lesions were placed within the ventral posterior nuclear complex of ten rhesus monkeys, all under barbiturate anesthesia, and the effects of the lesions on the cortical potentials evoked by stimulation of the contralateral lingual and hypoglossal nerves were observed. In addition, activity in response to hypoglossal and lingual nerve volleys was recorded from the ventral posterior nuclear complex. Both sets of data were consistent in indicating that hypoglossal afferents project to a restricted region of the nucleus ventralis posteromedialis which is confined to the anterodorsal portion of the nucleus. In contrast, the lingual nerve representation, as has been shown in other studies, occupies a much greater volume of VPM. The relationship between the lingual and hypoglossal nerve projections in VPM was discussed with respect to the relation shown to exist between superficial and deep modality projections in the nucleus ventralis posterolateralis.