Visuomotor properties of corticotectal cells in area 17 and posteromedial lateral suprasylvian (PMLS) cortex of the cat

We studied the visuomotor activity of corticotectal (CT) cells in two visua l cortical areas [area 17 and the posteromedial lateral suprasylvian cortex (PMLS)] of the cat. The cats were trained in simple oculomotor tasks, and head position was fixed. Most CT cells in both cortical areas gave a vigoro us discharge to a small stimulus used to control gaze when it fell within t he retinotopically defined visual field. However, the vigor of the visual r esponse did not predict, latency to initiate a saccade, saccade velocity, a mplitude, or even if a saccade would be made, minimizing any potential role these cells might have in premotor or attentional processes. Most CT cells in both areas were selective fur direction of stimulus motion, and cells i n PMLS showed a direction preference favoring motion away from points of ce ntral gaze. CT cells did not discharge with eye movements in the dark. Duri ng eye movements in the light, many CT cells in area 17 increased their act ivity. In contrast, cells in PMLS, including CT cells, were generally unres ponsive during saccades. Paradoxically, cells in PMLS responded vigorously to stimuli moving at saccadic velocities, indicating that the oculomotor sy stem suppresses visual activity elicited by moving the retina across an ill uminated scene. Nearly all CT cells showed oscillatory activity in the freq uency range of 20-90 Hz, especially in response to visual stimuli. However, this activity was capricious; strong oscillations in one trial could disap pear in the next despite identical stimulus conditions. Although the CT cel ls in both of these regions share many characteristics, the direction aniso tropy and the suppression of activity during eye movements which characteri ze the neurons in PMLS suggests that these two areas have different roles i n facilitating perceptual/motor processes at the level of the superior coll iculus.