This study will determine whether transcranial direct current stimulation (tDCS) can be used alter the amplitude of spontaneous neural activity, and thereby modulate cognitive function in healthy adults

An emerging neurological tool, called transcranial Direct Current Stimulation (tDCS), has recently been shown to safely and effectively enhance cognition in healthy individuals, as well as reduce key symptomatology in disorders such as stroke and depression, with only negligible side effects. tDCS delivers low-amplitude current to the scalp using small electrodes and part of this current passes through the skull and modulates neural activity in the underlying brain region. How this tiny amount of electric current acts to improve cognitive function and reduce symptoms (e.g., motor impairments in stroke patients with a lesion in motor brain areas) is currently unknown, although many investigators across the world are now working on this problem. Magnetoencephalography (MEG) offers a unique view of neural function, as it can delineate changes in active brain regions with excellent temporal resolution (< 1 ms) and high spatial accuracy (2-3 mm). MEG non-invasively measures the magnetic fields that emanate from active neocortical cells. The potential of the MEG technique to precisely monitor the neural effects of tDCS shows extreme promise, but to date the method has been rarely utilized in this area.

Under this protocol, Modulation of Spontaneous Cortical Activity by tDCS: BRAIN Initiative I, approximately 124 participants will provide written informed consent, undergo cognitive and behavioral testing and a structural MRI during a single visit, and then return several weeks later (2-4 weeks) to complete a short tDCS session followed by a MEG recording (i.e., after tDCS). Most participants will return for two more visits, each separated by 2-4 weeks, that include a tDCS session followed by a MEG recording (i.e., 4 total visits). The three tDCS-MEG visits will be identical except that the nature of the stimulation (e.g., location, amplitude, direction/polarity) will be different.

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 system (CNS) function as judged by the investigative team.
• History of clinically-significant head trauma.
• Pregnancy
• Any other condition that, in the opinion of the investigator, is a contraindication to participation
• The presence of any ferrous metal implant, including orthodontics (e.g., braces), which may interfere with the MEG data acquisition and/or be a MRI safety concern.
• Inability to correct visual acuity to 20/20 with corrective lenses (we can correct from +5 to -6 diopters in .5 diopter steps, separately for each eye, with non-magnetic corrective lenses in the laboratory).

Upon completion of the study, de-identified data from this study will be stored in the National Institute of Mental Health's (NIMH) Data Archive.

Data will be fully updated by the end of the study and will remain publicly available indefinitely.

Approval/Account from the NIMH

Of the 133 enrolled, 124 participants completed all interventions. The order of interventions was balanced and the goal was to identify the impact of the intervention and eliminate any effect of administration order.

Each participant was in the study for about one month (4 weeks).

Standard definitions for adverse events were used.

Focus on single stimulation amplitude and duration.

Double-blinded