VISUAL AND VESTIBULAR PROJECTIONS TO TONGUE MOTONEURONS

The rabbit hypoglossal neurons, localized in the mediocaudal part of t he XIIth nucleus receive visual and vestibular inputs able to induce r eflex responses functionally driven both to prepare the oral cavity fo r food reception and to ensure a correct postural arrangement of the t ongue. The aim of the present research was to show a possible converge nce of visual input on the hypoglossal neurons modulated by the vestib ular system and, thus, demonstrate that visual input plays a part in t he control of the tongue posture. It was found that 78% of tested neur ons responded to both photic stimulation of the retinae, performed by a conventional strobe unit, and electrical stimulation of the labyrint h, with different patterns of response. Moreover, visual input signifi cantly modified both the hypoglossal neuron response and the electromy ographic genioglossal response to caloric stimulation of the labyrinth . Because a significant visual influence on the hypoglossal nucleus re sponse and the genioglossal muscle response to labyrinthine stimulatio n was observed, it can be concluded that vision does integrate the spa tial information of the labyrinth to modulate thr postural tone of the tongue muscles.