Characterization of vestibular potentials evoked by linear acceleration pulses in the chinchilla

The objective of this study was to improve vestibular evoked potentials as a qualitative parameter for vestibular function in small laboratory animals. Linear upward acceleration pulses (up to 8 g within 1 ms) were applied to the head of anesthetized chinchillas. Electrophysiologic responses recorded by a chronically implanted electrode within the facial nerve canal consisted of an initial negative potential, labeled N1, within the first millisecond following the onset of acceleration. This potential was followed by a series of positive and negative potentials found to be highly labile to acoustic masking. The initial negative potential was only minimally sensitive to acoustic masking and persisted following surgical cochlear ablation, but completely disappeared following administration of potassium chloride into the inner ear. Recorded from the contralateral ear, N1 was unaffected by these procedures. Amplitudes of N1 decreased with attenuating stimulus intensity (1.45 microV/dB), whereby N1 latencies slightly increased (-0.015 ms/dB). These data, when coupled with the ability to completely abolish N1 with potassium intoxication while the contralateral ear remained intact, indicate that this potential represents electrophysiologic activity resulting from activation of the ipsilateral vestibular labyrinth.