Visual-vestibular interactions in the vestibular nuclei of the goldfish.

The responses of vestibular nuclei neurons of relaxed unanaesthetized goldfish have been examined with trapezoid velocity stimuli under three conditions. Responses to horizontal body rotation in the dark (pure vestibular stimulation) resemble those observed in vestibular nerve afferents. Optokinetic responses to exclusive visual surround-motion are also direction-specific and, in contrast to vestibular responses, exhibit a tonic response to constant velocity. They show three different response profiles, classified A,B or C, based on the neuron's discharge rate: either increasing, decreasing or remaining constant once surround motion is maintained at constant velocity. Following these dynamic effects, optokinetic responses have a maintained modulation of resting discharge until deceleration commences. The time constants associated with the dynamic effects vary between 1 and 11 seconds. Steady-state modulation of optokinetic responses shows a weak relation to stimulus velocities exceeding 10 deg/sec. Responses to body rotation in the light were found to linearly combine the weighted vestibular and optokinetic responses so that accurate velocity information is available for sensory and motor functions independent of the neuron's vestibular (I,II) or optokinetic (A,B,C) response type. The principle of this visual-vestibular interaction is discussed with respect to multisensory processing within the vestibular nuclei.