Compensation of oculomotor deficits in monkeys with neonatal cerebellar ablations.

The oculomotor performance of 11 monkeys, who had various degrees of cerebellar ablation shortly after birth, is described in this study. Detailed numerical results were obtained on three of these adult macaques after extensive training of specific pursuit eye movements and fixation. The vestibular nuclei were kept intact. In the presence of the intracerebellar nuclei, quite extensive neonatal ablations of the cerebellar cortex leave the adult monkey without any discernible oculomotor deficits. If ablation also includes the nuclei on one side, compensation is never complete even several years later: while vestibulo-ocular and saccadic responses seem normal, there are deficits in pursuit and gaze holding performance. The residual deficits vary with the extent of the ablation and are comparable with the pattern exhibited by acute hemicerebellar ablations. Monkeys who had their cerebellum including the nuclei essentially completely removed just after birth, could pursue, albeit with limited velocity, and hold gaze, albeit in a limited zone. Their vestibulo-ocular responses seemed unaffected.