SHORT-LATENCY VESTIBULAR EVOKED-POTENTIALS (VSEPS) TO LINEAR ACCELERATION IMPULSES IN RATS

In this study, short latency (t < 12.7 ms) vestibular evoked potential s (VsEPs) in response to linear acceleration impulses were recorded in 37 rats. A new technique (based on a solenoid) was used for generatin g linear force impulses that were delivered to the animal's head. The impulse had a maximal peak acceleration of 12 g. During the impulse, t he displacement was 50 mu m (at 4 g) and the rise time was 1.0 ms, A s timulation rate of 2/s was usually used. The VsEPs (averaged responses to 128 stimulations, digital filter: 300-1500 Hz) were recorded with electrodes on pinna and vertex, and were composed of 4-6 clear waves w ith mean amplitudes (for a 4 g stimulus) of 1-5 mu V. The VsEPs were r esistant. to while noise masking, and were significantly suppressed (P < 0.05) following bilateral application of a saturated KCl solution t o the inner ear, showing that contributions of the auditory and somato sensory systems are negligible. The latency of the response decreased as a power law function of stimulus magnitude, and the amplitude of th e first wave increased as a sigmoid function of stimulus magnitude. Vs EP responses were still present at the lowest intensities attainable ( 0.06-0.4 g) and reached saturation at 9 g. The amplitude of the later components was reduced when stimulus rate was elevated to 20/s. These results suggest that VsEPs in response to linear accelerations are sim ilar in their nature to VsEPs in response to angular acceleration impu lses that were previously recorded. These VsEPs to linear acceleration s are most likely initiated in the otolith organs. (C) 1997 Elsevier S cience Ireland Ltd.