TAC1 and major depressive disorder: The MHb is anatomically and histochemically different from the LHb.[35] MHb is involved in regulating higher brain functions, including mood, reward, attention, and decision making.[36, 37, 38] Studies have shown that MHb‐interpeduncular nucleus pathway and substance P play an important role in the pathogenesis of depression.[39, 40] Our studies further confirm the differences between MHb and LHb and the important function of MHb in regulating depression.