Electroconvulsive therapy (ECT) is a non-pharmacological treatment used in resistant depression whose effectiveness has been demonstrated. However, the brain mechanisms underlying this therapeutic effect remain unclear. Many animal studies show a neurotrophic action of ECT on the hippocampus: increased neurogenesis, synaptogenesis, proliferation of glial cells. In addition, functional imaging of "resting state" type have shown, among depressed patients after ECT, increased functional connectivity . These results were reinforced by the recent work of Perrin (2012). In view of this a priori contradictory, it seems appropriate to continue research neuroanatomical correlates subtending neurofunctional processes responsible at the same time improving the clinical depressive. The investigators suggest using an original technique never used in this type of population: Functional magnetic resonance imaging (fMRI) or multimodal structural-functional. This method will allow us to study the impact of ECT on brain structures involved in major depressive disorder: hippocampus.