The objectives of this study is to explore if there are any differences in neurobiochemistry, metabonomics and neuroimaging (1) at the baseline, between the subjects who are the normal controls (C Group) and who both meet diagnostic criteria of the Diagnostic and Statistical Manual of 5th edition (DSM-V) on MDD and TCM criteria of 'pattern of Liver Depression and Qi Stagnation (LDQS)' or'pattern of Deficiency of Both Heart and Spleen (DBHS)' (T Group); (2) at the baseline, between the MDD subjects of LDQS and DBHS; (3) after 6-week venlafaxine administration, between the MDD subjects of LDQS and DBHS. 50 subjects in T Group and 25 in C Group are recruited in the study and the main laboratory tests include High Performance Liquid Chromatography(HPLC), Gas Chromatography-Mass Spectrum(GCMS) and neuroimaging DTI technology.