Role of the extra-geniculate pathway in visual guidance. II. Effects of lesioning the pulvinar-lateral posterior thalamic complex in the cat.

Eight cats were trained to perform a paw movement towards a moving target. The target was a lever which moved at a variable speed across an aperture situated in front of the animal, from left to right or right to left at random, but only once per trial. The animals were trained until performances stabilized in terms of precision (correct movements versus misguided ones) and speed (response time distribution of correctly guided movements). Then they underwent bilateral electrolytic lesions restricted to the pulvinar nucleus (4 cats) or to the lateral posterior nucleus (4 cats). Pre- and postoperative performances were compared. The results showed a clear difference between the two nuclei; postoperative performances after pulvinar lesion were in the preoperative range, both for precision and response time, thus allowing this group to be considered as a control lesion group. On the other hand, a marked impairment in visual guidance followed lateral posterior lesions. This deficit affected both the precision and the speed of the response, with all cats showing a tendency to increase the response time of their efficient movements. This impairment disappeared progressively except for one animal, whose lesion was especially large. We suggest that the nucleus lateral posterior is involved in the control of visually guided movements; and its role as a component of the tecto-thalamo-cortical pathway is discussed.