Inactivation of Primate Superior Colliculus Biases Target Choice for Smooth Pursuit, Saccades, and Button Press Responses

In addition to its well-known role in the control of saccades, the primate superior colliculus (SC) has been implicated in the processes of target choice for overt orienting movements and for covert spatial attention. We focally inactivated the SC, by muscimol injection, while monkeys selected the target of a smooth pursuit, saccade, or button press response from two competing stimuli. The choice stimuli were placed so that one appeared within and the other appeared outside the affected visual field. SC inactivation biased the subject to choose stimuli out of the affected visual field for all three types of responses, although the effects on target choice were significantly smaller for button presses. Inactivation caused no changes in the selection of single stimuli within or out of the affected visual field, indicating the choice bias was not caused by deficits in response execution. The inactivation-induced bias for smooth pursuit and button press responses indicates SC activity is important for selecting the target, independent of any role in saccade preparation.