Role of the primary motor cortex (M1) in reward-based motor decision

Details

Supervisors

Duque, Julie ; Klein, Pierre-Alexandre

Faculty

Faculté des sciences de la motricité

Degree label

Master [60] en kinésithérapie et réadaptation

Abstract

enThe primary motor cortex (M1) was long thought to be the structure of pure motor functions. Nowadays, the concept of M1 is no longer that of a low-level output stage, but a highly plastic processor able to deal with decision making through a competition process occurring within M1 itself. Motor areas (especially M1) could be critical in integrating cognitive information, such as reward, that drives our decisions. We tested this hypothesis in humans by means of a finger selection task, in which subjects performed right index finger or right middle finger key presses according to an imperative signal. This signal was either obvious or ambiguous, but subjects were always asked to react as fast as possible. Hence, subjects had to respond at ‘random’ on a proportion of trials. A monetary reward based on the response’ accuracy and on the reaction times was provided after each response. Importantly, the score was manipulated, that is, it was higher in some condition (rewardpref and rewardnon-pref) that implicitly favors the use of the preferential finger. Using transcranial magnetic stimulation (TMS) over the dominant M1 in half the participant (TMS group), we induced a virtual lesion of this area thought to be involved in reward integration. For the control group (no-TMS group), we applied TMS over the non-dominant M1. Hence, we expected that, in the TMS group, no more reward-related learning could occur in M1. We measured the proportion of middle finger responses and compare the values obtained in the TMS group with respect to the no-TMS group. We found that subjects in the TMS group selected their preferential finger less than the ones of the no-TMS group. These results suggest that M1 is possibly involved in the integration of reward during motor decision.