Can a phone app train your brain to beat the blues?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Male or Female, between the ages of 18 and 80 at the time of screening. 2. Primary diagnosis of nonpsychotic major depressive disorder (MDD) without a history of psychotic features. 3. Score on the MADRS scale between 15-25 4. Able to read, understand, and provide written, dated informed consent prior to screening. Proficiency in English sufficient to complete questionnaires / follow instructions during fMRI. Stated willingness to comply with all study procedures, including availability for the duration of the study, and to communicate with study personnel about adverse events and other clinically important information. 5. Must possess an iPhone with the latest iOS version compatible with the app or must be willing to use a loaner iPhone from the study if available. 6. Has had at least one lifetime antidepressant treatment failure (ATHF) 7. The dose of the primary antidepressant medication (if applicable) must be stable for 4 weeks prior to baseline, and participants must agree to continue at this dose throughout the study period. 8. In good general health, as evidenced by medical history and determined by study physician 9. For women of reproductive potential: agree to the use of highly effective contraception during study participation. 10. Adequate visual acuity (with or without corrective lenses) to view study materials while in the MRI. 11. Agreement to adhere to Lifestyle Considerations throughout study duration. Exclusion Criteria: 1. Contraindication to MRI (ferromagnetic metal in their body) 2. Severe claustrophobia 3. Women that are pregnant or breastfeeding or with a positive urine pregnancy test at participation, or who are planning to become pregnant during the study period. 4. Primary psychiatric condition other than MDD requiring treatment except stable comorbid anxiety disorder 5. History of or current psychotic disorder, schizophrenia, psychosis, bipolar disorder, or severe borderline personality disorder. 6. Diagnosis of intellectual disability, autism spectrum disorder, or other neurodevelopmental disorder. 7. Current moderate or severe substance use disorder or demonstrating signs of acute substance withdrawal 8. Urine screening test positive for recent use of recreational drugs except for marijuana.. 9. Considered at significant risk for suicide during the course of the study. 10. Recent (within 4 weeks of any clinical effect) or concurrent use of rapid acting antidepressant agent (i.e., a course of ECT or TMS). Excluding ketamine. 11. History of significant neurologic disease, including dementia, Parkinson's or Huntington's disease, brain tumor, seizure disorder, subdural hematoma, multiple sclerosis, or history of significant head trauma as determined by the PD. 12. Untreated or insufficiently treated endocrine or metabolic disorder. 13. Any other condition deemed by the PD to interfere with the study or increase risk to the participant 14. Alexithymia as determined by the Toronto Alexithymia Scale 15. Treatment with an investigational drug or other intervention within the study period. 16. Not currently in a major depressive episode as defined by the MINI. 17. More than 5 lifetime adequate antidepressant medication failures (ATHF).