Visual and saccadic activity in the goldfish torus longitudinalis

Abstract

1. Multiunit activity was recorded in the torus longitudinalis (TL) of unanesthetized, immobilized goldfish while spontaneous eye movements were monitored with a search coil. Each saccade was accompanied by a burst of activity that started at the beginning of the saccade and peaked 120–150 ms later. Normally, the integrated burst amplitude was proportional to the saccade amplitude, but was independent of saccade direction or eye position. Saccadic bursts cannot be visual or proprioceptive in origin because they occur in the dark; are not evoked by passive eye movements; and persist after total paralysis with Flaxedil. Ablation of TL did not affect spontaneous eye movements. 2. Photic responses, also recorded in TL, were predominantly sustained multiunit discharges to dimming of the visual field of the contralateral eye. Diffuse receptive fields were located somewhat below the field equator, and mapped naso-temporally upon the rostro-caudal axis of TL. The photic responses of TL were more sustained and of longer latency than activity recorded simultaneously in the tectum. 3. Photic responses occurred more superficially in TL than the saccadic responses. Lesions of tectum abolished the photic response in the ipsilateral TL, but only attenuated the saccadic response. Lesioning the valvula, but not other parts of the cerebellum abolished the saccadic response of TL without affecting the photic response. After small lesions in the TL itself, saccadic responses were diminished, and sometimes depended upon the direction of eye movement, and the eye-in-orbit position. 4. It was concluded that the photic responses in one TL derive from a topographic input from the ipsilateral tectum. These responses are probably generated by a population of neurons different from those responsible for the saccadic responses. The latter originate in the valvula of the cerebellum, which apparently transmits information about saccade direction and eye position.