Design of the Study Patients will be randomized to receive 15 sessions of active rTMS or sham rTMS over the bilateral pre-SMA with a 1:1: ratio. After the randomized phase, all patients will undergo a 4 weeks washout phase. During the wash out phase each patients will be re-assessed every two weeks in order to detect long-lasting rTMS effects. At the end of the wash phase each patient will be classified as responder, partial responder or non-responder. After the washout phase responder patients will enter a follow-up phase up to 12 months while partial responders or non-responders in both the active and sham rTMS groups, will undergo an open phase of 15 sessions of active rTMS over the bilateral pre-SMA. After the open rTMS phase, all patients will undergo a 4 weeks washout phase. During the wash out phase each patients will be re-assessed every two weeks in order to detect long-lasting rTMS effects. Responder patients will then continue in the follow-up phase, while non-responder or partial responders will leave the study.