Modulation of Motor Cortex Excitability by TMS and tDCS (MAGS1)

Purpose of this pilot study is to modulate the motor cortex excitability by transcranial magnetic stimulation and transcranial direct current stimulation. Electromyography will be recorded on right abductor digiti minimi muscle to find the motor threshold and measure motor evoked potentials for each healthy participant. In addition, electroencephalography (EEG) data will be collected on the scalp with a high-density EEG net. Eighteen healthy participants will be in this study. Each participant will be seated in a reclining chair and applied non-invasive magnetic and electrical stimulations on the scalp. At baseline, the participant's resting motor threshold (RMT) will be estimated by adjusting the intensity of TMS applied on the left motor cortex to achieve motor-evoked potentials of about 50 uV with 10 TMS pulses at a rate of 0.25 Hz. Then a 3-condition, 3-session, 6-sequence randomized crossover experiment will be used to characterize and compare three versions of tDCS stimulation: anode, cathode, sham. Before and after a 10-min tDCS condition is applied, TMS pulses at 120% of RMT intensity will be applied for 10 minutes and TMS-evoked potential and motor-evoked potential amplitudes will be measured. Each session has at least 1-day gap to remove outlasting effects. We will also be collecting structural magnetic resonance imaging (sMRI) to target primary motor cortex precisely.

Inclusion criteria

• Male
• Between the ages of 18 and 35
• Right-handed
• Capacity to understand all relevant risks and potential benefits of the study (informed consent)
• Willing to comply with all study procedures and be available for the duration of the study
• Speak and understand English

Exclusion criteria

• Prior concussion
• Diagnosis of eating disorder (current or within the past 6 months)
• Diagnosis of obsessive compulsive disorder (lifetime)
• Attention-deficit/hyperactivity disorder (currently under treatment)
• Neurological disorders and conditions, including, but not limited to:

• History of epilepsy
• Seizures (except childhood febrile seizures and electroconvulsive therapy-induced seizures)
• Dementia
• History of stroke
• Parkinson's disease
• Multiple sclerosis
• Cerebral aneurysm
• Brain tumors
• Medical or neurological illness or treatment for a medical disorder that could interfere with study participation (e.g., unstable cardiac disease, HIV/AIDS, malignancy, liver or renal impairment)
• Prior brain surgery
• Any brain devices/implants, including cochlear implants and aneurysm clips
• Traumatic brain injury
• Anything that, in the opinion of the investigator, would place the participant at increased risk or preclude the participant's full compliance with or completion of the study