BDNF and major depressive disorder: Combined with the above demonstration that SIRT1/miR-134 can regulate hippocampal plasticity through CREB/BDNF and that exercise can upregulate the expression of BDNF, it is inferred that exercise can promote the increase in BDNF and CREB by improving the expression of SIRT1, thus improving synaptic plasticity, promoting neurogenesis, and relieving depression.