SPATIOTEMPORAL CHARACTERISTICS OF CENTRAL OTOLITH NEURONS

Purpose To review the spatiotemporal behaviours of central otolith neu rons in decerebrate animals. Data sources Laboratory of neurophysiolog y, Department of Physiology, Faculty of Medicine, The University of Ho ng Kong. Data extraction Results of key research findings from 1992 to 1997. Results With constant velocity colckwise (CW) and counterclockw ise (CCW) off-vertical axis rotations as stimuli to the otolith organs , neurons in the vestibular nuclei and medullary reticular formation s howed characteristic spatiotemporal behavious. One-dimensional neurons showed symmetric and stable bidirectional response sensitivities (del ta) to change in velocity while two-dimensional neurons showed asymmet ric and variable delta to velocity. This CW-CCW asymmetry to bidirecti onal rotations may provide directional coding in the modulation of neu ral signals. Vestibular nuclear neurons also displayed distinct sponta neous discharge patterns at the stationary and earth-horizontal positi on, indicating that one-and two-dimensional neurons belong to physiolo gically distinct etities. These spatiotemporal behavious of the vestib ular nuclear neurons were also shown to be precisely controlled by imp uts from the vestibulocerebellum and/or bilateral otoliths. In both th e vestibular nucleus and the reticular formation, the best response or ientations of one-dimensional neurons and the orientations of the maxi mum response vector of two-dimensional neurons were found to point in all directions close to the horizontal plane, indicating that ail head orientations on this plane are encoded across an ensemble of neurons. Conclusion Otolith-evoked behaviours of the one-dimensional and two-d imensional neurons constitute an important element for the recognition of the direction and orientation of head motion in space.