To determine the cognitive and neurophysiological dose-response relationships of anodal tDCS to the left DLPFC as a function of absolute current intensity, individualized E-field intensity, and stimulation duration.

To determine the cognitive and neurophysiological dose-response relationships of anodal tDCS to the left DLPFC as a function of absolute current intensity, individualized E-field intensity, and stimulation duration.

Inclusion Criteria (Patients)

1. Male and female outpatients 18-55 years of age
2. A diagnosis of ADD/ADHD or meeting the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria.
3. Patient will be either off stimulant medications or, if undergoing treatment with stimulants, will be asked to discontinue two days prior to the experiment, under physician-guided protocol, and allowed to resume afterwards. Subjects may resume stimulant use between the two study visits so long as they discontinue use two days prior to the second study visit. If fatigue is problematic in subjects discontinuing medication, they will be allowed to continue with the study if they are able to follow the suggested taper plan (50% of the dose day one, 25% dose day 2, stop day of visit (day 3)).
4. If on non-stimulant medications, dose must have been stable for at least 4 weeks.

Exclusion Criteria (Patients)

1. Contraindication to tDCS: history or epilepsy, metallic implants in the head and neck, brain stimulators, vagus nerve stimulators, VP shunt, pacemakers, pregnancy.
2. Active substance dependence (except for tobacco).
3. Pregnant or nursing females.
4. Inability to participate in testing procedures.

Inclusion Criteria (Healthy Control)

1. Male and female outpatients 18-55 years of age

Exclusion Criteria (Healthy Control)

1. Diagnosis of psychiatric of neurological disorder
2. Ongoing treatment with any psychotropic medications.
3. Contraindication to tDCS: history or epilepsy, metallic implants in the head and neck, brain stimulators, vagus nerve stimulators, VP shunt, pacemakers, pregnancy.
4. Active substance dependence (except for tobacco).
5. Pregnant or nursing females.
6. Inability to participate in testing procedures.