This article reviewed the beneficial effects of moderate voluntary physical exercise on brain health according to the studies on humans and animals, which includes improving psychological status and cognitive function, enhancing psychological well-being, decreasing the risks of Alzheimer＇s disease （AD） and dementia, and promoting the effects of antidepressant and anxiolytic. The possible underlying neurobiological mechanisms are involved up-active and down-active pathways. The up-active pathway is associated with enhancements of several neurotransmitters systems afferent to hippocampus, including norepinephrine （NE）, serotonin （5-Hydroxytryptamine, 5-HT）, acetylcholine （ACh） and γ-aminobutyric acid （GABA）. The down-active pathway is mainly concerned with up-regulation of the brain-derived neurotrophic factor （BDNF） and neurogenesis. It is suggested that NE activation via β-adrenergic receptors may be essential for exercise-induced BDNF up-regulation. The possible intracellular signaling pathways of NE-mediated BDNF up-expression may be involved in GPCR-MAPK-PI-3K crosstalk and positive feedback.
