VESTIBULAR COMPENSATION IN THE HORIZONTAL VESTIBULOOCULAR REFLEX OF THE GOLDFISH

Vestibular compensation is the process whereby vestibular system funct ion is restored following unilateral removal of the vestibular recepto rs (hemilabyrinthectomy). Vestibular compensation was studied in the h orizontal vestibule-ocular reflex (VOR) of the goldfish. Spontaneous V OR (spontaneous nystagmus) was not observed in the goldfish following recovery from the surgery for hemilabyrinthectomy (a period of about 3 0 min). However, hemilabyrinthectomy resulted in an acute decrease in the gain of the horizontal VOR to approx. 50% of normal, and an increa se in phase lead for mid-range frequencies (0.05 to 0.5 Hz). After 1 w eek of compensation, VOR gain had increased toward normal, and phase l ead had returned to normal levels for mid-range frequencies, but incre ased above normal at low frequencies. After 1 month of compensation, h orizontal VOR gain had recovered its normal value for head rotational velocity up to 60 deg/s, but it appeared to saturate for higher head v elocity, and phase lead had decreased to normal, and even slightly bel ow normal, at low frequencies. The results suggest that the goldfish i s capable of almost completely recovering both the gain and phase of t he horizontal VOR following 1 month of compensation for hemilabyrinthe ctomy. The extent of compensation in the horizontal VOR of the goldfis h is greater than that which has been reported for mammals.