Loss of relative-motion sensitivity in the monkey superior colliculus after lesions of cortical area MT.

Many cells in the superficial layers of the monkey superior colliculus are sensitive to relative motion. The response to a small stimulus moving through a cell's receptive field is strongly modulated by the relative motion between the stimulus and a textured pattern moving through the surrounding visual field; modulation is independent of absolute direction and speed of the stimulus. To determine whether cortical visual area MT is essential for this type of relative-motion sensitivity, colliculus cells were studied in the anesthetized, immobilized preparation after ablation of area MT. Unilateral MT lesions were made by either aspiration, kainic acid injection, or a combination of both methods. Data from the lesioned animals were compared with those from intact animals. Ipsilateral to the lesions, colliculus cells showed an almost total loss of sensitivity to relative motion. This loss was related neither to inadvertent injury of cortical areas neighboring MT nor to incidental optic radiation damage. Two other forms of motion-dependent, center-surround interactions were still present in the colliculus after the cortical lesions. These were a rudimentary sensitivity to differential motion between stimulus and background, which occurs for only one direction of stimulus movement, and a nonselective center-surround suppression, which is induced by movement of a background stimulus in any direction. Visual responsiveness, ocular dominance, and flash-evoked responses were also unaffected by the cortical lesions. We conclude that input from area MT is crucial for relative-motion sensitivity, but not for other response properties, in the superficial layers of the monkey colliculus.