Overnight Thalamic TES-TI to Modulate Sleep Spindles in Individuals With Schizophrenia Spectrum Disorders and Matched Healthy Controls

Inclusion Criteria (all participants): * U.S. citizen or holding permanent resident status * English-speaking Inclusion Criteria (Participants with SSD): * DSM-5 schizophrenia spectrum disorder (SSD) diagnosis, defined as schizophrenia, schizoaffective disorder, or schizophreniform disorder (confirmed by clinical interview and/or chart review) * Chronic illness, defined as diagnosis of SSD for at least 1 year * Clinically stable outpatient (no psychiatric hospitalization in past 6 months; no change in antipsychotic medication in the past 6 weeks) Inclusion Criteria (Healthy Controls): * Medically healthy (based on self-report and study team review) * Matched to SSD participants on age (±5 years) and sex Exclusion Criteria (all participants): * 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) * Active suicidal ideation, plan, or intent (assessed via PHQ-9 item 9 and follow-up Columbia-Suicide Severity Rating Scale (C-SSRS) Screener; see Safety Response Procedure) * Inability to provide informed consent, including inadequate decisional capacity in the judgment of the study team and/or study psychiatrist * History of head trauma resulting in prolonged loss of consciousness; or a history of \>3 grade I concussions * Current poorly controlled headaches, including intractabl…