Positive resource-based group reminiscence therapy for older adults with subthreshold depression: protocol for a three-arm randomized controlled trial

Subthreshold depression (StD) is common in later life and is associated with substantial health burden and an increased risk of progression to major depressive disorder. Reminiscence therapy is a feasible intervention for older adults, particularly in long-term care settings, but its effects may partly depend on the emotional characteristics of the cues used to evoke autobiographical memories. Conventional reminiscence interventions rarely select or standardize nostalgic materials by emotional valence. This study will evaluate whether group reminiscence therapy incorporating standardized positive nostalgic resources produces greater improvement in depressive symptoms than traditional reminiscence therapy, and will explore potential mechanisms underlying its effects. This assessor-blinded, three-arm randomized controlled trial will be conducted in multiple nursing homes in Changchun, China. Eligible older adults with StD will be randomly assigned in a 1:1:1 ratio to positive reminiscence therapy (PRT), traditional reminiscence therapy (TRT), or a waitlist control (WLC). Interventions will comprise 8 weekly 45–60-min group sessions. PRT will use standardized positive nostalgic resources, including photographs, music, and videos selected by prespecified affective criteria, whereas TRT will use nostalgic resources without positive-valence selection. Outcomes will be assessed at baseline, mid-intervention (week 4), post-intervention (week 8), and 3 months (week 20). The primary outcome will be depressive symptoms measured using the 15-item Geriatric Depression Scale (GDS-15) at week 8. Secondary outcomes will include anxiety, positive and negative affect, self-identity, life satisfaction, hope, and autobiographical memory specificity. The primary analysis will use a linear mixed-effects model accounting for repeated measurements and therapy-subgroup clustering in both active intervention arms. Exploratory mediation analyses will examine whether mid-intervention changes in autobiographical memory and positive affect predict subsequent changes in depressive symptoms. By comparing positive resource-based reminiscence therapy with an active reminiscence intervention and a waitlist control, this trial will estimate the incremental benefit of incorporating affectively selected nostalgic resources into group reminiscence therapy. The longitudinal assessment of autobiographical memory and affect will also provide preliminary evidence on how positive nostalgic cues influence depressive symptoms. The findings may inform the development of more standardized and theoretically grounded reminiscence interventions for older adults with StD in long-term care settings. Chinese Clinical Trial Registry (ChiCTR), ChiCTR2600129905, registered on 11 August 2026.