To evaluate the effects of a two-week anodal tDCS regimen on the left dorsolateral prefrontal cortex, focusing on functional connectivity changes in neural networks in MCI patients resulting from various possible underlying disorders, considering individual factors associated to AD such as amyloid-beta deposition, APOE ε4 allele, BDNF Val66Met polymorphism, and sex. The gene discussed is BDNF; the disease is Alzheimer disease.