Optimizing Volunteer Comfort for Transcranial Electrical Stimulation (TES): An Assessment

Inclusion criteria - healthy adult men and non-pregnant, non-lactating women aged 18-39 years, inclusive. Exclusion criteria - The following exclusion criteria apply to all volunteers, are consistent with those used in our other sleep studies, and are applied in this protocol in order to obtain a sample of volunteers who are likely to be representative of future study populations: * Self-reported habitual nightly sleep amounts outside the target range of 6-9 hours (i.e., less than 6 hours per night or more than 9 hours per night, on average): * Nighttime lights-out times earlier than 2100 hours on average during weeknights (Sunday through Thursday) for the past month * Morning wake-up times later than 0900 on average during weekdays (Monday through Friday) for the past month. * History of cardiovascular disease (to include but not limited to arrhythmias, valvular heart disease, congestive heart failure, history of sudden cardiac death or myocardial infarction) * Reported habitual napping (\> 3 times a week in conjunction with normal sleep habits) * Resting blood pressure above 140/90 * Resting pulse \> 110 * Neurologic disorder (to include but not limited to epilepsy or another seizure disorder, amnesia for any reason, hydrocephalus, MS, narcolepsy or other sleep disorders) * Kidney disease * History of psychiatric disorder requiring hospitalization or psychiatric medication for any length of time * Beck Depression Inventory score of 14 or above * Underlying pulmonary disease requiring daily inhaler use * Regular nicotine use (or addiction) (defined as more than 1 cigarette or equivalent per week) within the last 1 year * Positive nicotine/cotinine screen as determined by NicCheck™ I test strips * Heavy alcohol use to be determined by the PI or his/her representative (minimum limit to define heavy alcohol use is 14 drinks per week) * Use of other illicit drugs (to include but not limited to benzodiazepines, amphetamines, cocaine, marijuana) * Known liver disease or liver abnormalities as determined by a laboratory test * Self-reported history of caffeine use in excess of 400 mg (approximately 8 caffeinated sodas or 3-4 cups of coffee) per day on average * Pregnancy (females) * Inability to read and sign consent * Use of certain medications (including use of vitamins or supplements), to be determined on a case-by-case basis by the examining study licensed physician. * BMI ≥ 30 (Obese Class I or greater) * The PI also maintains the prerogative to disqualify a volunteer if it is deemed that the volunteer's participation would be unsafe for the volunteer or staff or would be disruptive to study conduct.