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Robert M. McPeek, Edward L. Keller; Deficits in saccade target selection after temporary inactivation of superior colliculus. Journal of Vision 2002;2(7):573. doi: 10.1167/2.7.573.
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© ARVO (1962-2015); The Authors (2016-present)
During tasks which require selecting one eye-movement target from among several possibilities, neurons recorded in the primate superior colliculus (SC) show responses consistent with a role in saccade target selection. However, it is possible that this SC activity is merely a passive read-out of target-selection processes occurring in cortical areas that project to the SC, such as the frontal eye field (FEF) and lateral intraparietal area (LIP). In order to determine whether the SC plays an active role in the target selection process, we induced changes in SC activity (using small injections of lidocaine or muscimol) and tested subsequent performance in single-target and target-selection tasks. When a single saccade target is presented inside the portion of the visual field affected by the injection, monkeys show relatively minor motor impairments, including smaller saccade amplitudes, lower movement velocities, and longer latencies. If the SC were not involved in saccade target selection, and were merely involved in movement execution, impairments in the target-selection task would be similar to those seen with a single stimulus. However, we found that local inactivation of the SC causes major target-selection deficits in a pop-out visual search task: when the target is presented inside the affected field, monkeys execute relatively accurate saccades, but the saccades are often directed to a distractor stimulus rather than to the target. No deficits are seen when the target is presented outside the affected field. Control experiments show that the target-selection deficits are not due to a low-level visual impairment within the affected field, nor can they be explained as a simple motor impairment, since saccades to single stimuli in the affected field can still be made. These results indicate that the SC plays an active, functional role in the network of brain areas underlying saccade target selection.
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