The study will test the hypothesis that mindfulness-based neurofeedback (mbNF) will improve repetitive negative thinking and social and role functioning over sham neurofeedback in adolescents at risk for serious mental illness. To do so, 90 adolescents ages 14-21 with elevated repetitive negative thinking will be enrolled into a double-blind randomized clinical trial of sessions of mindfulness training with either active mindfulness-based neurofeedback or sham neurofeedback and three months of mindfulness practice and follow up.

Approximately 90 at-risk adolescents ages 14-21 years old will be enrolled in a double-blind, randomized clinical trial. All participants will undergo a baseline clinical assessment (Visit 1), which will serve as an important baseline for daily symptom fluctuation and use of mindfulness strategies prior to training. Approximately 1-2 weeks after the baseline assessments, all participants will complete an in-person visit (Visit 2) in which they will complete a brief MRI scan (resting state localizer) and a 45-minute mindfulness training. After the mindfulness training, participants will be randomized in a 1:1 ratio to receive either active or sham neurofeedback (n=45 each group). Randomization will be stratified by information obtained at the baseline assessment: biological sex, prior daily/near daily mindfulness practice for 8 weeks or more. A study staff member with no participant contact will create randomization tables in REDCap to alloacte participants to either active or sham mbNF. Participants and staff will remain blinded to assignment. Participants will then complete another MRI session what will include resting state scans as well as the active or sham mbNF. Approximately 1-2 weeks later, participants will return for another in-person visit (Visit 3) that includes a mindfulness refresher and repeats the procedures of Visit 2. Participants will briefly rate their mindfulness practice daily for three months using a brief, online survey. At 1-, 3- and 12-months post-neurofeedback, participants will complete self-report and clinician-rated assessments to probe repetitive negative thinking and prodromal psychiatric symptoms.

Inclusion Criteria:

• Ages 14-21, inclusive
• Recurrent negative thinking, defined as PTQ-C (<18 years) or PTQ (18 years or older) total score >30 and at least two questions scored 3 or 4.
• Able to understand study procedures, read, and write in English
• If age is 18 years or older: Competent and willing to provide written informed consent
• If age is less than 18 years: Competent and willing to provide written informed assent AND have a parent/legal guardian who is competent and willing to provide written informed consent
• Access to a mobile device to complete daily survey assessments

Exclusion Criteria:

• Any of the following lifetime mental health disorders by DSM-V criteria: psychotic disorders, anxiety disorder, bipolar disorder, oppositional defiant disorder, conduct disorder, developmental disorder (e.g., autism), post-traumatic stress disorder, or eating disorder
• Substance use disorder, moderate or severe in past six months.
• Unstable medical or neurologic condition, epilepsy or seizure disorder, head injury, loss of consciousness >5 minutes
• MRI contraindications (i.e. presence of ferromagnetic implants, cardiac pacemaker or pacemaker wires, metallic particles in the body, vascular clips in the head or previous neurosurgery, prosthetic heart valves, magnetic dental implants claustrophobia).
• Visual, auditory, or cognitive impairment (IQ<80 based on the Wechsler Abbreviated Intelligence Scale (WASI)) that may make it difficult to participate.
• Any condition or situation that would, in the investigator's opinion, make it unlikely that the participant could adhere safely to the study protocol.
• Pregnancy; a negative pregnancy test is required at enrollment
• Individuals who are under the legal protection of the government or state (Wards of the State)
• Inability to speak, read, or write English fluently

The data that support the findings of this study are available upon request. Data will include de-identified individual patient-level data and a data dictionary. Investigators proposing to use the data must execute a data use agreement with Massachusetts General Hospital and have approval from an Institutional Review Board (IRB), Independent Ethics Committee (IEC), or Research Ethics Board (REB), as applicable, before data is shared. Data will be available within three months of manuscript publication. Requests for data should be sent to aeevins@mgh.harvard.edu.

Beginning 3 months and ending 5 years following manuscript publication.