VISUAL-AUDITORY INTERACTIONS MODULATE SACCADE-RELATED ACTIVITY IN MONKEY SUPERIOR COLLICULUS

This paper reports on single-unit activity of saccade-related burst ne urons (SRBNs) in the intermediate and deep layers of the monkey superi or colliculus (SC), evoked by bimodal sensory stimulation. Monkeys wer e trained to generate saccadic eye movements towards visual stimuli, i n either a unimodal visual saccade task, or in a bimodal visual-audito ry task. In the latter task, the monkeys were required to make an accu rate saccade towards a visual target, while ignoring an auditory stimu lus. The presentation of an auditory stimulus in temporal and spatial proximity of the visual target influenced neither the accuracy nor the kinematic properties of the evoked saccades, However, it had a signif icant effect on the activity of 90% (45/50) of the SRBNs, The motor-re lated burst increased significantly in some neurons, but was suppresse d in others. In visual-movement cells, comparable bimodal interactions were observed in both the visually evoked burst and the movement-rela ted burst. The large differences observed in the movement-related acti vity of SRBNs for identical saccades under different sensory condition s do not support the hypothesis that such cells encode dynamic motor e rror. The only behavioral parameter that was affected by the presentat ion of the auditory stimulus was saccade latency. Auditory stimulation caused saccade latency changes in the majority of the experiments. Me anwhile, the timing of peak collicular motor activity and saccade onse t remained tightly coupled for all stimulus configurations. In additio n, saccade latency varied as function of the distance between the stim uli in 36% of the recordings. Interestingly, the occurrence of a spati al latency effect covaried significantly with a similar spatial influe nce on the SRBNs firing rate. These cells were always most active in t he bimodal task when both stimuli were in spatial register, but activi ty decreased with increasing stimulus separation. (C) 1998 Elsevier Sc ience Inc.