BDNF and major depressive disorder: The effective mechanism of Qigong may be attributed to Qigong training increasing excitation of the middle cerebral cortex, which has been shown to modulate the hypothalamic-pituitary-adrenal axis [57–58], monoamine neurotransmitter [57], brain-derived neurotrophic factor [57] and adiponectin [59] to alleviate severe psychological symptoms, such as anxiety and depression.