Short-term adaptation of saccades does not affect smooth pursuit eye movement initiation

Abstract

Scrutiny of the visual environment requires saccades that shift gaze to objects of interest. In case the object should be moving, smooth pursuit eye movements (SPEM) try to keep the image of the object within the confines of the fovea in order to ensure sufficient time for its analysis. Both saccades and SPEM can be adaptively changed by the experience of insufficiencies, compromising the precision of saccades or the minimization of object image slip in the case of SPEM. As both forms of adaptation rely on the cerebellar oculomotor vermis (OMV), most probably deploying a shared neuronal machinery, one might expect that the adaptation of one type of eye movement should affect the kinematics of the other. In order to test this expectation, we subjected two monkeys to a standard saccadic adaption paradigm with SPEM test trials at the end and, alternatively, the same two monkeys plus a third one to a random saccadic adaptation paradigm with interleaved trials of SPEM. In contrast to our expectation, we observed at best marginal transfer which, moreover, had little consistency across experiments and subjects. The lack of consistent transfer of saccadic adaptation decisively constrains models of the implementation of oculomotor learning in the OMV, suggesting an extensive separation of saccade- and SPEM-related synapses on P-cell dendritic trees.

Pontine Lesions Impair Visually Guided Eye and Hand Movements

“…Recent work (Junker et al 2018) has callenged this view and suggests a more complicated influence of the olivary signal. Sun and co-workers (Sun 2017) showed the separation of adaptation-mechanisms of saccades on one hand and SP on the other in the OMV of nonhuman primates suggesting a separation of saccade- and SP-related synapses on P-cell dendritic trees.…”