Other non‐imaging primary brain health outcomes were: EEG (27 studies, 7.4%); BDNF levels (11 studies, 3.0%); cognitive testing (one study, 0.3%); the Beck depression score (one study, 0.3%); and serum τ and amyloid β levels (one study, 0.3%). This evidence concerns the gene TBXT and major depressive disorder.