The study was approved by the ethics review committee of Yu Quan Hospital, and written informed consent was obtained from all participants prior to the commencement of the study. Patients with MDD were recruited from inpatient departments of Yu Quan Hospital from September 2013 to August 2016. The diagnoses of all patients were established by the Structured Clinical Interview according to the DSM-IVTR (SCID). Exclusion criteria include: 1) age less than 18 or over 60 years; 2) left-handed which is evaluated by Edinburgh handedness inventory; 3) major physical illnesses such as malignant tumor, chronic renal failure, severe heart disease, and severe respiratory disease; 4) other psychiatric disorders and neurological disorders; 5) substance abuse; 6) took medication within the 3-month period prior to the study; and 7) received electroconvulsive therapy. Finally, 40 patients were include in the present study. Twenty-three right-handed healthy controls (HC) were recruited from the local community by advertisements. Age, gender and educational level were matched between MDD groups and HC. The control subjects were screened using the non-patient edition of the SCID to confirm the lifetime absence of a history of psychiatric or neurological disorders and were interviewed to exclude family history of psychiatric illness.