Dorsal cerebellar vermis lesions impair adaptive gain control of saccadic and pursuit eye movements

Purpose. To find out if the dorsal cerebellar vermis participates in adaptive gain control of saccades and pursuit eye movements. Methods. Three rhesus monkeys (A, B, C) were trained to follow targets. Eye movements were measured with the search coil method. Saccade gain adaptation was induced with a double step paradigm in which the target jumped back by 30 % during the saccade. Adaptation of the initial (100 ms) acceleration of pursuit was induced by a step-ramp paradigm in which target speed doubled or halved 200 ms after the target began moving. The dorsal cerebellar vermis of each monkey was surgically aspirated. Results. Post-lesion, monkeys developed saccadic dysmetria (A: hypometria (79 % of pre-lesion amplitude), B: hypermetria (128 %), C: hypometria (80 %)) with greater SD (A: 1.4, B: 1.9, C:2.3 times pre-lesion value). Saccade gain adaptation was nearly completely lost (< 20 % of pre-lesion value) in A and B but intact in C. Post-lesion, initial acceleration of pursuit decreased (A: 74 %, B: 94 %, C: 84 % of pre-lesion value) but without change in variability. Pursuit adaptation was also impaired (A: 89 %, B: 40 %, C: 61 % of pre-lesion value for gain increase paradigm, A: 45 %, B: 75 %, C: 38 % for gain decrease paradigm). Conclusion. The dorsal cerebellar vermis is important for control of saccade gain and pursuit initiation and for adaptive modification of these parameters.