BDNF and major depressive disorder: Studies were included for review if they met all the following criteria: (1) published research articles investigating the association between BDNF and PSD or post-stroke depressive mood in recent two decades; (2) study participants were adults (≥18 years of age), with clinical diagnoses of PSD or evaluations of depression scores conducted in stroke patients, and objective assessments of BDNF levels performed for all participants; (3) changes in BDNF levels in stroke patients were clearly described; (4) peer-reviewed articles published in English.