In the current study, the investigators aim to understand the role of transcranial direct current stimulation (tDCS) in improving executive function across neuropsychiatric populations known to have deficits in this cognitive domain. The investigators will select 8 relevant diagnostic categories: traumatic brain injury, major depressive disorder, bipolar disorder, schizophrenia, attention deficit hyperactivity disorder, borderline personality disorder and substance use disorder. The study will also include a cohort of healthy controls for comparison.
