BDNF and depressive symptom measurement: As the Met allele of the Val66Met gene may also be associated with structural and functional changes of prefrontal cortical areas (Liu et al., 2012; Kim et al., 2013), as well as decreased white matter integrity in frontal lobe tracts (Ziegler et al., 2013; Tatham et al., 2016), it might be reasonable to expect that the BDNF genotype would moderate the relations between loneliness, self-efficacy, and depression.