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