BDNF and depressive disorder: Chang et al. [15] studied 45 patients with subacute stroke and found that serum BDNF levels were significantly and positively correlated with scores on the Geriatric Depression Scale short form (GDS-SF) at each of three time points: before the start of the study, one week, and two weeks after the clinical trial (r = .480, p = .013; r = .477, p = .014; r = .480, p = .013, respectively).