Abstract
The primate superior colliculus (SC) is important for the execution of saccadic eye movements, but recent evidence suggests that it also plays a role in the higher-level process of target selection for saccadic and pursuit eye movements, as well as in covert attention shifts. Thus, we speculated that SC activity may participate in a generalized salience map used for target selection for a variety of purposes. To test this hypothesis, we recorded the activity of isolated intermediate-layer SC neurons in monkeys trained to perform a reach target selection task. The monkeys were rewarded for maintaining fixation and reaching to touch an odd-colored target presented in an array of distractors. Even though no eye movements were made in this task, many neurons discriminated the target before the onset of the reach, and this activity typically persisted throughout the trial, consistent with SC involvement in target selection for reaching movements. To further determine if this SC activity plays a causal role in reach target selection, we tested the effects of temporary focal SC inactivation on monkeys' performance in two reach target selection tasks. In one task, a target was followed after a variable SOA by a distractor, and monkeys were rewarded for reaching to the target. In the second task, two potential targets were shown and a cue at the fovea indicated which was the target. Monkeys were required to maintain eye fixation throughout each trial. In both tasks, after SC inactivation, when the target appeared in the inactivated part of the visual field, monkeys made more reaching errors to the distractor. In contrast, monkeys were unimpaired when the target was presented without distractors. These results establish that, in addition to its role in saccades, the SC plays a causal role in target selection for reaching movements.
National Eye Institute grant R01-EY014885, Core grant P30-EY006883, and R.C. Atkinson Fellowship Award.