The intervention group (N=68) will include participants with Huntington's disease (N=34) and Parkinson's disease (N=34). Participants will download the MindTrails-Movement app with active CBM-I training condition and will be prompted to complete brief, daily CBM-I training sessions for a period of 6 weeks. They will complete surveys assessing mood symptoms and interpretation bias at baseline, end of week 2, end of week 4, and end of week 6 (end of intervention), then again at the end of week 10.

The waitlist control group (N=68) will include participants with Huntington's disease (N=34) and Parkinson's disease (N=34). Participants will be asked to download a control version of the app that includes access to a list of support resources but does not include daily CBM-I training content. They will complete surveys assessing mood symptoms and interpretation bias at baseline, end of week 2, end of week 4, and end of week 6, and end of week 10. Waitlist control participants will be offered the opportunity to complete the intervention version of the app after they complete their final study assessments.

CBM-I training app with active CBM-I training condition

Patient-reported anxiety symptoms will be measured using the Quality of Life in Neurological Disorders Anxiety short form (NeuroQoL-Anxiety) total raw scores. This measure includes 8 items ranked 1-5, where the total score is the sum of item scores (range 8-40), and higher scores indicate worse anxiety symptoms.

Movement Disorders Interpretation Bias Scale (MDIB) is a measure of interpretation bias in people with movement disorders. Participants rate the likelihood (0-4) of three alternate explanations (two benign and one negative) for why an ambiguous event occurred. To obtain negative external and internal bias scores, the mean of 5 negative ratings for external threats (Items 3c, 5a, 7a, 10a, 11c) and the mean of 4 negative ratings for internal threats (Items 1b, 4c, 8b, 12b) will be computed, where higher scores (possible range: 0-4) reflect more severe negative interpretation biases.

Patient-reported depressive symptoms will be measured using the Quality of Life in Neurological Disorders Depression short form (NeuroQoL-Depression) total raw scores. This measure includes 8 items ranked 1-5, where the total score is the sum of item scores (range 8-40), and higher scores indicate worse depressive symptoms.