Modulation of Spontaneous Cortical Activity by tDCS: BRAIN Initiative I

Inclusion Criteria: * Informed consent obtained from the participant. * Age: 19-35 years of age at enrollment or 55-72 years of age at enrollment. * Gender: males and females included. * Right-handed based on the Edinburgh Handedness Inventory * Cognitive functioning: Intelligent Quotient (IQ) of 85 - 115 on the Wechsler Adult Intelligence Scale-Revised * Ability to complete the questionnaires in English, as not all the neuropsychological tests and questionnaires have been validated in other languages. Exclusion Criteria: * Current use of the following medications: psychotropic medications or other medications with significant CNS effects (e.g., antipsychotics, psychostimulants, anticonvulsants, alpha-agonists, adrenergic blockers, lithium, and sedating antihistamines), or other excluded medication. * Current psychiatric diagnosis based on the Mini-International Neuropsychiatric Interview (MINI) and/or the adult attention-deficit/hyperactivity disorder (ADHD) diagnostic interview. * Current substance abuse or substance dependence at any time. * The presence of a known neurological disorder or any major medical illness or injury impacting neurological/psychiatric function (e.g., diabetes, epilepsy, cerebral palsy, traumatic brain injury, significant environmental/toxic injury, neurodegenerative disorder, past meningitis/encephalitis). * General medical conditions: any major medical conditions that would interfere with involvement in the study or may affect central nervous s…