Evaluation of the Prophylactic Efficacy of tDCS in Chronic Migraine

Consenting patients will report on a book, all of their migraine attack for 1 month. Then they will be randomized to the active tDCS group or sham tDCS group. Patients will have one session of tDCS per day during the first week, then one session per week for a month and finally a session every 15 days for 1 month. After tDCS sessions, patients will be followed for 3 months. Throughout their participation in the study, patients will complete their migraine record (1month of base line before tDCS, 2 months during tDCS, 3 months after tDCS). Patients will have 5 evaluation examinations: * The first, one before tDCS, * The second, 1 month after the beginning of tDCS * The third, immediately after the end of tDCS * The fourth, 1 month after the end of tDCS * And the last one, 3 months after the end of tDCS. The physician responsible for conducting tDCS sessions will make the randomization via a website. The physician in charge of the evaluation examinations will don't know the allocated treatment.