ID: Intradimensional; ED: Extradimensional; CANTAB: Cambridge Neuropsychological Test Automated Battery; EEG: Electroencephalography; vLTP: Visual long-term potentiation; Y-BOCS: Yale-Brown Obsessive Compulsive Scale; MADRS: Montgomery-Asberg Depression Rating Scale; PROM: Patient-reported outcome measure; BDNF: Brain-derived neurotrophic factor. This evidence concerns the gene BDNF and major depressive disorder.