Heart-Smile Training (HST) is a compassion and loving-kindness-based intensive introduction program consisting of a 3-day retreat, 4-weeks of weekly 2 hour meetings, and a 1-day final retreat. This study is a randomized controlled trial study to evaluate the effectiveness of Heart-Smile Training as compared to the passive control group on measures of neural, physiological, and clinically-relevant outcomes among individuals with symptoms of depression. Participants will be randomized to either the HST group or a waitlist control group. Both groups will complete assessments before and after HST including electroencephalography (EEG), electrocardiogram (EKG), electrodermal activity tests, and self-report surveys. All study activities except surveys will be conducted in person.

This will be a randomized controlled trial with two arms: Heart-Smile Training Intensive Introduction Program (HST-IIP) vs. a waitlist control group. These two arms will be compared on measures of neural, physiological, and clinically-relevant outcomes.

The investigators will enroll up to 50 adult volunteers from the general population from the ages of 18 to 65 with depression, with Computerized Adaptive Test- Depression Inventory (CAT-DI) scores from 35-75. Volunteers interested in the study will be consented and screened for their eligibility. Eligible participants will be randomized to join either the HST-IIP arm or a waitlist control arm after completing all baseline assessments and the EEG session.

Both the HST-IIP and waitlist arm will complete a baseline measurement session between study weeks -3 to 0, before starting any group sessions. Prior to completing the baseline measurement section, they will be randomized to either HST-IIP or the waitlist arm. Participants enrolled in the HST-IIP arm will join the intervention group between week 1 to 5. The waitlist arm will not join any program between week 1 to 5. They will continue their treatment as usual without any change in their therapy session or medication. Both arms will complete weekly survey measures for 5 weeks. Both arms will then complete a post measurement session during study weeks 5 to 7.

At both baseline and post-intervention measurement sessions, all participants will complete in-person study tasks and remote surveys. In-person study visits will include neurophysiological measures; EEG, EKG, skin conductance, and respiration rate measures and will take place at the Spaulding Rehabilitation Hospital/Mass General Brigham in Charlestown, MA. Remote self-report surveys will be completed by participants during baseline and post-measurement either at home through a link secure to the Cambridge Health Alliance (CHA) REDCap database sent via email or using an electronic device at the CHA Center for Mindfulness and Compassion.

Inclusion Criteria:

• Sufficient English fluency to understand procedures and questionnaires
• Ability to provide informed consent
• Mild to moderately severe depression (CAT-DI score 35-75) (Achtyes et al., 2015; Gibbons et al., 2012)

Exclusion Criteria:

• Cognitive inability as demonstrated by Montreal Cognitive Assessment (MOCA) <24 OR the inability to complete consent quiz and baseline assessments (Nasreddine et al., 2005);
• Current participation in another research study;
• Unavailable or unable to participate in planned dates for the HST-IIP sessions;
• Expected hospitalization during the study period, including second and third trimester pregnancy at screening;
• Expected incarceration during the study period;
• Previous experience with mindfulness or other mind-body practices, defined as more than 10 minutes of practice per day, more than 5 days a week for the past 6 months; participation in an 8-week mindfulness group program in the last 2 years; or participation in a meditation retreat longer than 1 day in the past 2 years;
• Inability to successfully complete in-person study sessions with EEG, EKG, respiration rate, and skin conductance response measurement as determined by the principal investigator;
• Inability to participate safely in the study intervention and without disrupting the group (in the opinion of principal investigator OR meeting any of the following criteria):
• Active psychosis defined by a PSY-S-CAT score > 60 (from the CAT-MH assessment) will trigger the requirement of a clinical assessment prior to participation in the program (Achtyes et al., 2015)
• Bipolar I disorder history or severe level of mania on CAT-MH (score >70) (Achtyes et al., 2015): In addition, current use of mood stabilizing medication for bipolar disorder.
• Severe depression, indicated by CAT-DI > 75 (Achtyes et al., 2015; Gibbons et al., 2012)
• Acute homicidality with plan and/or intent;
• Acute suicidality or hospitalization for suicide attempt or self-harm within three months of the enrollment period;
• Severe Borderline Personality Disorder or other severe personality disorder that may lead to disruptions within the group; and/or
• Moderate or severe Substance Use Disorder. In addition, reported use of illicit drugs (i.e., cocaine, methamphetamine) OR non-prescribed controlled medications (opioids, stimulants, or benzodiazepines) in the past 3 months.