Role of the extra-geniculate pathway in visual guidance. I. Effects of lesioning the superior colliculus in the cat.

We investigated the effect of superior colliculus lesions on the performance of a visually guided paw movement. Six cats were trained to perform a paw movement toward a lever moving in front of them at an adjustable speed. The target was visible and accessible for approximately 700 ms, corresponding to the time needed to traverse the aperture situated in front of the animal. To receive a food pellet reward the cat had to press on the lever during this presentation period. Efficient and misguided movements were recorded, and their relative proportions calculated. For each rewarded movement, the response time (delay between the appearance of the lever in the aperture and the cat's press) was automatically computed. After stabilization of their performance, each cat underwent a bilateral electrolytic lesion of the superior colliculi. In all cases it markedly affected precision. The cats first recovered their ability to reach an immobile lever and later on their ability to point to the lever while it was moving. However, even after two months of postoperative training, two cats had still not completely recovered their preoperative precision. All lesioned animals displayed a perturbation in their response time distribution. Anterior lesions, involving area centralis projection, were more effective in producing the deficits than more posterior ones. The results are discussed in relation to the involvement of the superior colliculus in the analysis of peripheral fixed or moving stimuli.