Changes in gain of the vestibulo-ocular reflex induced by combined visual and vestibular stimulation in goldfish.

Adaptive changes in the vestibulo-ocular reflex (VOR) of goldfish were produced in a few hours by sinusoidally rotating restrained fish in the horizontal plane inside a vertically striped drum. The drum could also be sinusoidally rotated so that the gain of the VOR (the ratio of eye to head angular velocity) would have to increase to two or decrease to zero in order to maintain a stable retinal image. During 'training' towards two VOR gain measured at the stimulation frequency of 0.125 Hz increased rapidly over 6 h of stimulation to about 1.5 from an initial gain of 0.7. Half of that change occurred in the first 30 min. During training towards zero VOR gain measured at the stimulation frequency decreased to 0.15. About one-third of that change occurred in the first 30 min. Testing at different sinusoidal frequencies after 6 h stimulation showed that increases in VOR gain were generated across a 6-octave range; however, reductions in gain were produced over a narrow frequency range close to the training frequency. Gain reductions occurred more rapidly on a second day of stimulation. In a paradigm simulating reversing prisms, partial reversal of the VOR was observed in some fish. However, these fish also demonstrated spontaneous slow sinusoidal eye movements that may have represented a different means of adjusting eye movements to stabilize the retinal image. Goldfish provide a useful preparation for the study of adaptive gain changes in vertebrate oculomotor systems.