1 2 Vestibulo - Ocular Reflex Adaptation Investigated with Chronic Motion - 3 Modulated Electrical Stimulation of Semicircular Canal Afferents . 4 5 Richard

26 To investigate vestibulo-ocular reflex (VOR) adaptation produced by changes in 27 peripheral vestibular afference, we developed and tested a vestibular “prosthesis” that 28 senses yaw-axis angular head velocity and uses this information to modulate the rate of 29 electrical pulses applied to the lateral canal ampullary nerve. The ability of the brain to 30 adapt the different components of the VOR (gain, phase, axis, and symmetry) during 31 chronic prosthetic electrical stimulation was studied in two squirrel monkeys. After 32 characterizing the normal yaw-axis VOR, electrodes were implanted in both lateral canals 33 and the canals were plugged. The VOR in the canal-plugged/instrumented state was 34 measured and then unilateral stimulation was applied by the prosthesis. The VOR was 35 repeatedly measured over several months while the prosthetic stimulation was cycled 36 between off, low-sensitivity, and high-sensitivity stimulation states. The VOR response 37 initially demonstrated a low gain, abnormal rotational axis, and substantial asymmetry. 38 During chronic stimulation the gain increased, the rotational axis improved, and the VOR 39 became more symmetric. Gain changes were augmented by cycling the stimulation 40 between the off, low, and high-sensitivity states every few weeks. The VOR time 41 constant remained low throughout the period of chronic stimulation. These results 42 demonstrate that the brain can adaptively modify the gain, axis, and symmetry of the 43 VOR when provided with chronic motion-modulated electrical stimulation by a canal 44 prosthesis. 45