Saccadic disorders caused by cooling the superior colliculus or the frontal eye field, or from combined lesions of...

We used reversible cold lesions to explore the oculomotor consequences of separate and combined dysfunction of the superior colliculus (SC) and the frontal eye field (FEF). Two monkeys were trained to fixate visual targets. In one we measured visually driven saccades while cooling the right SC, first alone, then in combination with bilateral FEF ablation. Two cryodes in the other subject permitted measurement of eye movements during cooling of either the right FEF or the right SC, or both structures together. Cooling FEF mainly caused a neglect. Raising the cryode temperature slightly alleviated the neglect and uncovered a subtle saccadic deficit. It consisted of a slight reduction in saccadic amplitude and increase in saccadic reaction time. Cooling the SC alone lengthened saccadic reaction time and reduced saccadic amplitude more dramatically, causing the monkeys' initial saccade to miss the target. Some correction occurred but a targeting error persisted to the end of the trial. Combined lesions of FEF and SC greatly increased reaction times, reduced saccadic amplitude, and caused large and persistent targeting errors. The changes in saccadic amplitude and the targeting errors were a function of the monkey's eye position. Combined lesions also truncated the ocular range of the monkeys.