Somatosensory input from the forelimb nerves to the hypoglossal neurons

Our results showed that hypoglossal neurons localized in the mediocaudal part of the XIIth nucleus modulate their firing in relation to somatosensory information travelling along the forelimb nerves. Large evoked potentials and responses of single hypoglossal units were recorded during electrical stimulation of the common radial nerve of both sides. A spinohypoglossal pathway has not been described before, but our results indicate this possibility. The latencies of the hypoglossal responses to somatosensory stimulation suggest that somatic afferent volleys may stop at the reticular level and contact the XIIth nucleus through a spinoreticulohypoglossal pathway. Previous work showed that visual and vestibular input contact the same mediocaudal region of the hypoglossal nucleus. Thus it is possible that the postural arrangement of the tongue is subject to a complex control depending on the vestibular, visual, and somatosensory system.