Study hypothesis: psychotherapy and SSRI treatment effect in different brain way: psychotherapy in "up to down" way and SSRI in "down to up" way. The investigators will explore this hypothesis in major depressive disorder outpatients with Magnetic Resonance Imaging analysis in this study. Patients in different groups will be treated by psychotherapy or SSRI treatment. They will all be checked with Magnetic Resonance Imaging pro and after 12 weeks of treatment.