BDNF and major depressive disorder: Decreased BDNF levels and mutations in genes associated with BDNF signaling have been associated with hippocampal dysfunction (Egan et al., 2003), memory impairment (Egan et al., 2003), increased risk for depression (Martinowich et al., 2007; Erickson et al., 2012), schizophrenia (Angelucci et al., 2005), and anxiety (Egan et al., 2003; Martinowich et al., 2007; Erickson et al., 2012).