Role of the SMA During Unimanual and Bimanual Movements Preparation: the Mirror Movements Paradigm

The aim of the project is to study the role of secondary motor area (more precisely the supplementary motor area, or SMA) during unimanual and bimanual voluntary movements externally (cue) or internally (subject's choice) triggered. In that view, we will study 3 experimental groups :

* a group of healthy volunteers (control group) * the same group of healthy volunteers after a transient inactivation of the SMA (by the aim of repetitive trans cranial magnetic stimulation or TMS) * a group of patients suffering from congenital mirror movements who are suspected to present a dysfunction of the SMA (according to our previous results) In each of these groups, by the aim of a serial reaction time task, we will study the influence of a SMA stimulation on the excitability of the primary motor cortex (M1) during the preparation of a voluntary movement (unimanual or bimanual). This will allow us to assess the communication between the SMA and M1 during movement preparation. Using the same task in functional imagery, we will study the activation's pattern of primary and secondary motor areas during movement preparation. This multimodal approach should allow us to better understand the synergistic functioning of these different structures involved in movement preparation. An other interesting aspect will be to determine the role of these structures in movement lateralization. Eventually, our results might allow us to precise to role of the motor preparation's dysfunction in the genesis of congenital mirror movements.

In the first place, this study aims at a better understanding of the cerebral physiology of movement preparation (which is not well known) using the mirror movements paradigm as a dysfunction model (according to our previous results). According to our hypothesis, there is a strong link between the SMA and M1 during movement preparation. This hypothesis will be assessed by the use of the same experimental task with combined neurophysiological and neuroimaging approaches, thus increasing the validity of the results obtained.

A secondary aim of this protocol is to precise the role of motor planning dysfunction in patients with congenital mirror movements. A better understanding of the mechanisms responsible for this condition is necessary in a medium-term therapeutic prospect.