Direct evidence for the contribution of the superior colliculus in the control of visually guided reaching movements in the cat.

The production of visually guided reaching movements relies on a large neural network. Based on indirect experimental evidence, it has been suggested that the superior colliculus, a subcortical centre known for its key role in controlling rapid orienting gaze shifts, also belongs to this network. The aim of the present study was to investigate the role of the cat superior colliculus (SC) in the control of visually guided reaching movements. To address this issue, we studied the effect of SC electrical stimulation on forelimb reaching movements in two cats trained to catch a piece of food. Electrical stimulation delivered just after the movement onset yielded a consistent perturbation of the movement trajectory of the forelimb extremity. This perturbation followed stimulation onset by 56 +/- 11 ms on average, and consisted of a deviation of the spatial path and a deceleration of the movement. The forelimb perturbation was elicited in the absence of concomitant gaze or head displacement in 52% of the stimulation trials. Forelimb perturbations were followed by in-flight adjustments so that reaching movements reliably ended on the target. The present results constitute the first behavioural evidence for a contribution of the cat SC to the control of visually guided forelimb movements.