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A PUTATIVE ROLE FOR THE CEREBELLUM IN AVIAN VESTIBULAR RESPONSES TO LINEAR TRANSLATION.    S. Irons-Brown¹, S.M. Jones², and T.A. Jones^{1, 2}. ¹Dept of Physiology, and ²Surgery/ENT, University of Missouri-Columbia.

There have been a number of studies that have identified the higher order central relays involved in generating auditory brain stem responses (ABR). Similarly, vestibular responses elicited by acceleration pulses, also known as vestibular evoked potentials (VsEPs), are generated by peripheral and central relays. Specifically, VsEP response components P1 and N1 are generated by the vestibular portion of the peripheral eighth nerve, whereas response components beyond P2 are generated by central relays (Nazareth and Jones, 1998, J.Vestib.Res. 8, 233-252). However, little is known about which central relays are involved. The purpose of the present study was to determine the involvement of the cerebellum in generating avian vestibular evoked potentials (VsEPs). Linear acceleration pulses were used to elicit VsEPs before and after aspiration of the cerebellum in eleven- to fourteen-day-old chicks (Gallus domesticus). Response peak latencies (e.g., P1, P2, P3, P4) and amplitudes (e.g., P1/N1, P2/N2, P3/N3, P4/N4) were then measured and compared between pre and postoperative conditions. Animals were grouped into two categories: 1) those where more than 50% of the cerebellum was removed, and 2) those where less than 50% had been removed. The results revealed, on average, that both groups of animals demonstrated major reductions in the amplitude of P2/N2. In animals where more than 50% of the cerebellum had been removed, reductions were also apparent for P4/N4. No changes were seen for response peak latencies. The results support the hypothesis that the cerebellum is involved in the generation of VsEPs to linear acceleration stimuli.

(Supported by NASA NAG5 4607 and NIH R01 DC04477.)