The goal of this clinical trial is to find out whether a type of electrical brain stimulation, called temporal interference stimulation, can temporarily change the way different parts of the brain communicate with each other.

Participants will:

• Complete two stimulation phases - overnight and during wakefulness
• Undergo two MRIs per study phase

This study will evaluate the effectiveness of personalized thalamic temporal interference transcranial electrical stimulation (TI-TES) to modulate thalamocortical activity and connectivity in healthy adults. Using a within-subject, counterbalanced crossover design, participants will complete two stimulation phases: (1) repeated overnight TI-TES or sham stimulation during NREM sleep and (2) repeated during quiet wakefulness. Each phase consists of two sessions. Phases are separated by a ≥4-week washout. Resting-state functional magnetic resonance imaging (fMRI) will be acquired before and after each phase to assess sustained changes in thalamocortical functional connectivity, with high-density EEG providing secondary measures of brain-state-specific oscillatory modulation (sigma/spindles in sleep, alpha in wake).

Inclusion Criteria:

• Adults aged 18-50
• Medically healthy
• U.S. citizen or holding permanent resident status
• English-speaking

Exclusion Criteria:

• Any current or past history of neurological disorders or acquired neurological disease (e.g. stroke, traumatic brain injury), including intracranial lesions (including clinically significant findings identified in first MRI)
• History of inpatient psychiatric hospitalization
• History of head trauma resulting in prolonged loss of consciousness; or a history of greater than 3 grade I concussions
• Current history of poorly controlled headaches including intractable or poorly controlled 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
• 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
• Any medication that may alter seizure threshold taken during the study i.e., Attention-deficit/hyperactivity disorder (ADHD) stimulants (Adderall, amphetamine); Tricyclic/atypical antidepressants (amitriptyline, doxepin, imipramine, maprotiline, nortriptyline, bupropion); SSRIs (Escitalopram, Fluoxetine, Sertraline); Antipsychotics (chlorpromazine, clozapine), Bronchodilators (theophylline, aminophylline); Antibiotics (fluoroquinolones, imipenem, penicillin, cephalosporins, metronidazole, isoniazid); Antivirals (valacyclovir, ritonavir); over the counter antihistamines (diphenhydramine, Benadryl); Estradiol-based birth control
• Claustrophobia (a fear of small or closed places)
• Back problems that would prevent lying flat for up to two hours
• Regular night-shift work (second or third shift)
• Sleep apnea or other sleep disorder (self-reported)