SPONTANEOUS ACTIVITY OF OTOLITH-RELATED VESTIBULAR NUCLEAR NEURONS INTHE DECEREBRATE RAT

The discharge properties of lateral and descending vestibular neurons responsive to constant velocity off-vertical axis rotations (OVAR) in thr clockwise (CW) and counterclockwise (CCW) directions. were studied at the stationary and earth-horizontal position of decerebrate adult rats. From the coefficient of variation (CV), the spontaneous activiti es of OVAR-responsive neurons were classified into regular and irregul ar patterns. Of the neurons (it = 36)that showed symmetric and stable bidirectional response sensitivity (delta defined as CW gain over CCW gain) to QVAR (10 degrees tilt), some exhibited progressive phase shif t with velocity (1.75-15 degrees/s) while others exhibited stable resp onse phase. Most neurons of the former group (93% or 12/13) showed reg ular discharge pattern while only 22% (n = 5/23) of the latter group s howed such a pattern. Though the phase-stable neurons showed a signifi cantly higher average CV than the phase-shifted neurons, there was no significant difference between the mean spontaneous firing rates of th ese neurons. The neurons (ii = 17) that showed asymmetric and Variable delta to OVAR velocity can also be grouped - those that exhibited a g reater gain with rotations directed towards the side of recording (I n eurons) showed irregular discharge pattern while those that exhibited a greater gain with rotations directed towards the side contralateral to recording (C neurons) showed regular discharge pattern, The I and C neurons also exhibited significant difference in mean firing rates. n le relationship between the response characteristics of the OVAR-respo nsive neurons and their spontaneous activity at the stationary and ear th-horizontal position is discussed.