BDNF and depressive symptom measurement: Although the pathophysiology of depression has not yet been fully elucidated, the typically assumed molecular biologic causes include a lack of monoamines such as serotonin, noradrenaline, and dopamine; hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis (Stetler and Miller, 2011); neuroinflammation (Schiepers et al., 2005); BDNF dysfunction; decreased gamma-aminobutyric acid (GABA) activity; and glutamate system dysfunction (Maletic et al., 2007; Hasler, 2010).