Increased neuroplasticity of BDNF is implicated in neurotrophic theories of depression and its treatment (Caddy et al., 2014) since there is robust evidence that serum BDNF concentrations are decreased in depressed individuals and that antidepressant treatment regulates its levels (Duman, 2004; Sen et al., 2008). Here, BDNF is linked to major depressive disorder.