Mechanistic Validation of Human Multipolar TES-TI: Amplitude Modulation, Frequency, and Benchmarking

Inclusion Criteria:

* Medically healthy (based on self-report and study team review)
* U.S. citizen or holding permanent resident status
* English-speaking (able to provide consent and complete questionnaires)

Exclusion Criteria:

* Current or past history of clinically significant neurological disorder or acquired neurological disease (e.g., stroke, traumatic brain injury), including intracranial lesions (including clinically significant findings identified on the structural MRI)
* History of inpatient psychiatric hospitalization
* History of head trauma resulting in prolonged loss of consciousness; or a history of \>3 grade I concussions
* Current poorly controlled headaches, including intractable or frequent migraines
* Any systemic illness or unstable medical condition that may cause a medical emergency in case of a provoked seizure (cardiac malformation, cardiac dysrhythmia, asthma, etc.)
* History of seizures, diagnosis of epilepsy, history of abnormal (epileptiform) EEG, or family history of treatment resistant epilepsy except for a single seizure of benign etiology (e.g. febrile seizures) in the judgment of a board-certified neurologist
* Possible pregnancy or plan to become pregnant in the next 6 months (self reported)
* Any metal in the head or body
* Any medical devices or implants (i.e. cardiac pacemaker, medication infusion pump, cochlear implant, vagal nerve stimulator)
* Dental implants
* Permanent retainers
* Any hair braid, dreadlocks, hair pieces, or extensions which cannot be taken out before the study sessions
* Any head coverings or headdress that participant feels uncomfortable removing for the purposes of study sessions
* Current use of medications known to substantially lower seizure threshold, specifically chlorpromazine, clozapine, bupropion, clomipramine, or maprotiline; or other medications at doses known to substantially lower seizure threshold in the judgment of the PI
* Active scalp lesions, broken skin, or skin conditions at planned electrode sites that would preclude safe electrode application
* Claustrophobia (a fear of small or closed places)
* Back problems that would prevent lying flat for up to two hours