These studies suggest that individuals with the BDNF Val66Met polymorphism might be at risk for a smaller prefrontal cortex and hippocampus, leading to the susceptibility to mood disorders, which strengthens the hypothesis that BDNF plays an important role in depression (Montag et al., 2009; Yu and Chen, 2011; Duman, 2017). Here, BDNF is linked to depressive symptom measurement.