Mechanisms of Change in Cognitive Behavioral Therapy for Insomnia (CBTi)

Inclusion Criteria: * Aged 50-65 * Normal hearing with or without hearing aids * Ability to speak and read English and ability to give informed consent * Possession of a computer with video and audio capabilities * Meets DSM-5 Criteria for Insomnia Disorder * Internet speed sufficient for participating in teletherapy (e.g., Zoom Health) or SHUTi (for iCBTi group) * MoCA scores ≥24 will be deemed normal cognitive status and considered eligible for study participation and/or assessed by the ability to comprehend the baseline screening questionnaires * Willing to refrain from new external behavioral health or medication treatment for issues pertaining to sleep during participation in the study * Indication that the individual plans to be in the area for the 6 months following the first baseline assessment Exclusion Criteria: * Failure to meet the above "inclusion criteria" * Current circadian rhythm disorder, sleep deprivation, or hypersomnia and related sleep disorders (assessed with clinical interview and/or self-report) as CBTi has not been validated in these populations. Verified by self-report and/or clinical interview (SCISD-R) * Untreated sleep disordered breathing (e.g., obstructive sleep apnea) assessed by self-report, clinical interview, and/or diagnostic sleep study (i.e., baseline sleep study PSG) * Failing to meet criteria for MRI scan (e.g., having metallic implants); see Pre-screen MRI Checklist for full list of exclusions for MRI scans. * Fear/phobia of needles (conflict with blood draw) and/or small spaces (conflict with MRI scanner) * Current suicide risk meriting crisis intervention as assessed by the Patient Health Questionnaire (PHQ-9) and/or disclosure of serious suicidal ideation * Pregnancy (self-report, proposed instruments and treatments have not been validated in this population) * Sleep efficiency \> 85%, assessed by the sleep diary * Serious mental health diagnosis (e.g., bipolar disorder or psychosis) assessed by structured interview (M.I.N.I.) * Currently engaged in evidence-based psychotherapy for Insomnia (i.e., Cognitive Behavioral Therapy) by self-report * Failure to follow protocol (e.g., consistent "no show" for appointments, answering questionnaires dishonestly, refusal to complete more than 2 assessments \[e.g., fMRI and Neuropsych\])