RESPONSES OF FLOCCULAR PURKINJE-CELLS TO SINUSOIDAL VERTICAL ROTATION AND EFFECTS OF MUSCIMOL INFUSION INTO THE FLOCCULUS IN ALERT CATS

To understand how the flocculus is involved in the integration process in the vertical VOR, we examined the responses of floccular Purkinje cells during whole-body rotation in many vertical and horizontal planes in alert cats. The great majority of cells that responded to pitch rotation received excitation from the contralateral posterior canal, whereas the minority received excitation from the anterior canal, either on the ipsilateral or contralateral side; 35% of these vertical canal responding cells received convergent inputs, either from the ipsilateral or contralateral horizontal canal. After infusion of a GABA agonist (muscimol) into the area where many posterior canal responding Purkinje cells were recorded, the downward VOR induced by nose-up pitch was selectively impaired at low stimulus frequencies, together with an impairment of gaze holding after downward saccades. These results indicate a crucial role for posterior canal responding floccular Purkinje cells in generating downward eye position signals. Since the flocculus inhibits VOR interneurons related to the anterior and horizontal canals but not the posterior canal (Ito, 1984), our results suggest the possibility that posterior canal responding floccular Purkinje cells may form a transfloccular inhibitory pathway to anterior canal related VOR interneurons. This pathway may facilitate the positive feedback effect in the vestibular commissural inhibitory pathway between the co-planar vertical canals for the posterior canal signal, and may thereby be specifically involved in integration in the vertical VOR.