Revisiting sensorimotor adaptation: new insights from inter-task transfer of after-effects in prism adaptation

The plasticity that characterizes our nervous system enables us to realize smooth and precise movement despite varying demands. The understanding and distinction of processes enabling to modify existing movements when facing a perturbation (adaptation) or to learn new ones (learning) represents a crucial challenge. Sensorimotor adaptation is reflected not only by the gradual error reduction during the perturbation but mostly by the presence of after-effects once the perturbation is removed. The nature of after-effects provides information concerning the modifications entailed in the sensorimotor system and thus the type of processes involved.

The aim of this thesis was to shed light on the comprehension of sensorimotor plasticity processes. More precisely, we hypothesized that the transfer of after-effects to a task that has not been performed under the perturbation might uncover the contribution of distinct processes during sensorimotor adaptation. Therefore, the objective was to isolate the characteristics of processes favouring transfer. In addition, we aimed at investigating the role of the cerebellum in these processes.

To complete these objectives, we used a behavioural approach through a prism adaptation paradigm, using googles laterally shifting the visual field. Our first study showed a transfer of after-effects acquired during pointing prism exposure to a throwing task. However, the transfer from throwing to pointing was possible only for experts in throwing. Thus, the expertise on the task performed during prism exposure strongly influenced the nature of processes at work to face the perturbation. In the second study, we demonstrated that prism adaptation by motor imagery of pointing movements under exposure led to substantial transfer to throwing movements. This was the case only for participants with high motor imagery abilities. Finally, using tDCS, the two last studies emphasized the possible role of the cerebellum in after-effects transfer.

Altogether, these results underline the interest to study inter-task transfer of after-effects to unravel the contribution of distinct processes during sensorimotor adaptation, beyond the classical measure of after-effects. We propose that the development of transferable after-effects relies on sustained adjustments of the internal models in the sensorimotor system.

These modifications may be guided by sensory prediction errors and controlled by cerebellar regions. In a translational view, these fundamental findings pave the way for clinical perspectives of research to optimize the transfer of compensations from rehabilitation context to other daily life situations in patients with motor disorders.

Key words:  sensorimotor plasticity, adaptation, learning, after-effects, transfer, prism adaptation, internal models, cerebellum, tDCS, motor imagery