Vestibular compensation in the horizontal vestibulo-ocular reflex of the goldfish

Vestibular compensation is the process whereby vestibular system function is restored following unilateral removal of the vestibular receptors (hemilabyrinthectomy). Vestibular compensation was studied in the horizontal vestibulo-ocular reflex (VOR) of the goldfish. Spontaneous VOR (spontaneous nystagmus) was not observed in the goldfish following recovery from the surgery for hemilabyrinthectomy (a period of about 30 min). However, hemilabyrinthectomy resulted in an acute decrease in the gain of the horizontal VOR to approx. 50% of normal, and an increase in phase lead for mid-range frequencies (0.05 to 0.5 Hz). After 1 week of compensation, VOR gain had increased toward normal, and phase lead had returned to normal levels for mid-range frequencies, but increased above normal at low frequencies. After 1 month of compensation, horizontal VOR gain had recovered its normal value for head rotational velocity up to 60 deg/s, but it appeared to saturate for higher head velocity, and phase lead had decreased to normal, and even slightly below normal, at low frequencies. The results suggest that the goldfish is capable of almost completely recovering both the gain and phase of the horizontal VOR following 1 month of compensation for hemilabyrinthectomy. The extent of compensation in the horizontal VOR of the goldfish is greater than that which has been reported for mammals.