The goal of this study is to monitor the brain using electroencephalography (EEG) while transcranial direct current stimulation (tDCS) is being administered, as a potential pathway to determine neurophysiological markers capable of forecasting the intensity of a subject's response to tDCS.

Transcranial direct current stimulation is a non-invasive neuromodulation technique that has been the subject of many recent investigations. There is a growing body of evidence to suggest that tDCS can enhance the efficacy of various therapies. However, progress in the field is slow: many studies suffer from reproducibility issues, or highly variable results, including stroke rehabilitation. It is feasible that much of the variance in experimental results can be explained by an inability to quantitatively track individual responses to tDCS in real-time, and personalize stimulation parameters for maximum effect.

Monitoring the brain via EEG while tDCS is being administered is a potential pathway to determine neurophysiological markers capable of forecasting the intensity of a subject's response to tDCS. This research has not previously been attempted due to technical difficulties- namely, the electromagnetic interference that is associated with tDCS degrades EEG signal quality. Recent advances in electrode and amplification technology have made it possible to make EEG recordings simultaneously with tDCS.

The investigators will attempt to determine whether specific EEG signatures can indicate the magnitude of a tDCS response. Subjects will receive either real or sham anodal tDCS to the hand representation of their left primary motor cortex.

The efficacy of the tDCS protocol will be quantitatively determined using transcranial magnetic stimulation (TMS) to generate a motor-evoked potential (MEP) in the hand pre- and post-tDCS. Additionally, prior to, during, and following the tDCS protocol, we will record EEG event-related potentials (ERPs) in response to a finger-tapping (motor) task.

The investigators aim to draw a correlation between the magnitude of MEP changes and pre- and post-tDCS and changes in recorded ERPs before, during and after tDCS in order to quantify the response to tDCS over the motor cortex. If EEG metrics can be used to gauge efficacy in real-time during tDCS administration, the investigators will gain significant insight into how to appropriately and quantitatively individualize tDCS dosage parameters for each patient.

Inclusion Criteria:

• Neurologically healthy

Exclusion Criteria:

• Ongoing use of CNS-active medications

• Ongoing use of psychoactive medications, such as stimulants, antidepressants, and anti-psychotic medications

• Presence of a potential tDCS/TMS Risk Factor:

  1. Damaged skin at the site of stimulation (i.e. skin with ingrown hairs, acne, razor nicks, wounds that have not healed, recent scar tissue, broken skin, etc)
  2. Presence of an electrically, magnetically or mechanically activated implant (including cardiac pacemaker), an intracerebral vascular clip or any other electrically sensitive support system
  3. Metal in any part of the body, including metal injury to the eye (Jewelry must be removed during stimulation)
  4. A history of medication-resistant epilepsy in the family
  5. Past history of seizures or unexplained spells of loss of consciousness

There is no plan to make individual participant data available to other researchers at this time.