tDCS and Prismatic Adaptation: Roles of the Cerebellum and the Primary Motor Cortex in the Transfer of After-effects

Human beings are able to produce precise and smooth movements despite varying demands thank to the nervous system plasticity. Primastic exposure is a method that allows to easily study these sensorimotor plasticity processes in a laboratory context. In a typical protocol, participants wear prismatic goggles that induce a lateral deviation of the visual field while performing a goal directed motor task (e.g. pointing). During the first trials, participants make errors in the direction of the deviation and correct them trial-by-trial. Finally, participants go back to baseline performances after a few dozen of trials. Upon goggles removal, participants make mistakes toward the direction opposition to the initial prismatic deviation. These after-effects reflect adaptive processes that occurred to counteract the perturbation. The way that these after-effects can be transferred to other situations which have not been exposed to the prismatic perturbation bring crucial information about the nature of the processes involved. Additionally, these transfer properties might be of great interest in the field of neuro rehabilitation. In fact, the purpose of therapeutic strategies is to induce compensations that can be transferred to daily life situations.

In previous studies, the investigator showed that expertise on the exposed had a notable influence on transfer properties. However, these studies did not allow to identify the cerebral regions involved in transfer.

The cerebellum is described as a major area implied during motor adaptation and the occurrence of after-effects, while the primary motor cortex might play a crucial role in the formation of motor memory. As such, these two regions are likely to be involved in transfer properties.

The objective of this project is to identify the roles of the cerebellum and the primary motor cortex in the transfer of visuomotor compensations acquired during prism exposure to task that has not been practiced under the perturbation. To do so, the investigator will use transcranial direct current stimulation (tDCS) which is a non-painful and non-invasive functional brain stimulation method. Several groups will be constituted to test if stimulation (inhibitory and excitatory) of the cerebellum or the primary motor on the transfer of prism acquired compensations to a non-exposed task. More precisely, the investigator aim to study the influence of different stimulation modalities (cerebellum vs MA, inhibitory vs excitatory vs sham) on the error reduction during prism exposure, on the amount of after-effects and on the amount on transfer to the non-exposed task.

On a fundamental level, this project will allow a better understanding of the sensorimotor plasticity processes involved to counteract a perturbation and about mechanisms underlying transfer properties. Future results would allows to shed light on the conditions necessary to give rise to transfer as well as the implied brain regions. On longer-term these results will be used to optimize rehabitation strategies in motor function recovery in order to favour the transfer of acquired compensations to daily life situations.


Eligibility Criteria:
Inclusion Criteria:

* Male or female
* Right-handed
* Aged 18 to 70
* Normal or corrected vision
* Signed written informed consent
* Affiliated to a health care organism.

Exclusion Criteria:

* Neurological or psychiatric disorder
* Pregnancy
* Epilepsy antecedents
* Presence of metallic implant, pace maker, cochlear implant, chirurgical brain clip.
* Cognitive disorders
* presence of corrective eyeglasses
* Right upper limb orthopedic disorders