These processes further influence brain-derived neutotrophic factor (BDNF) production leading to long-term potentiation (anodal tDCS) or depression (cathodal tDCS) (14, 15), and produce post-modulatory synaptic changes, with long-term potentiation strengthening connections between neurons and long-term depression weakening them (16). This evidence concerns the gene BDNF and depressive symptom measurement.