Neuromodulation for treatment-resistant depression: a narrative review and clinical translation framework

Abstract

Treatment-resistant depression (TRD) is a common and disabling clinical problem associated with persistent symptoms, functional impairment, relapse risk, suicidality, and high health-system burden. Neuromodulation has become an increasingly important treatment pathway because it directly modulates neural circuits implicated in mood regulation rather than relying exclusively on pharmacological mechanisms. To review and critically synthesize current evidence on neuromodulation for TRD, with emphasis on electroconvulsive therapy, repetitive transcranial magnetic stimulation (rTMS), intermittent theta-burst stimulation (iTBS), transcranial direct current stimulation, vagus nerve stimulation, deep brain stimulation, safety, clinical translation, and implementation challenges. We conducted a structured narrative review of clinically relevant literature identified through searches of PubMed/MEDLINE, Scopus, Web of Science, guideline repositories, and reference lists. The search was intended to improve the breadth and transparency of the narrative synthesis and was not conducted as a formal systematic review. No protocol was registered, and no duplicate screening, formal risk-of-bias assessment, certainty-of-evidence evaluation, or quantitative synthesis was performed. The literature supports a provisional multidimensional clinical-positioning framework rather than a head-to-head efficacy hierarchy. Electroconvulsive therapy remains the most established intervention for severe, psychotic, catatonic, suicidal, or life-threatening depression. Repetitive transcranial magnetic stimulation is a validated non-invasive outpatient treatment with favorable tolerability and expanding protocol options. Intermittent theta-burst stimulation provides similar clinical utility with shorter sessions, whereas accelerated and image-guided iTBS protocols are promising but require further replication, durability, and maintenance data. Transcranial direct current stimulation, including supervised home-based models, is being investigated as a potentially scalable approach, but its TRD-specific evidence and real-world implementation remain less established than those of rTMS. Vagus nerve stimulation and deep brain stimulation may benefit selected highly refractory patients, but delayed response, invasiveness, cost, evidentiary heterogeneity, and long-term device-management requirements limit routine use and largely restrict these modalities to specialized services. Neuromodulation may be incorporated as a staged, protocol-based component of multidisciplinary TRD care where appropriate expertise, infrastructure, and follow-up are available, rather than being viewed as a single interchangeable device category. Broader adoption requires standardized definitions, individualized targeting, maintenance planning, adverse-event monitoring, equitable access, and pragmatic implementation research. Neuromodulation is a clinically important therapeutic domain for treatment-resistant depression, ranging from established non-invasive treatments to emerging personalized circuit-based interventions. The most reproducible clinical support currently favors electroconvulsive therapy for urgent or severe depression and repetitive transcranial magnetic stimulation as an evidence-based outpatient option after inadequate pharmacotherapy response. Intermittent theta-burst stimulation (iTBS) can improve treatment feasibility through shorter sessions, whereas accelerated delivery of iTBS may shorten the overall treatment course but remains resource-intensive and insufficiently standardized for broad routine dissemination. Vagus nerve stimulation is a regulatory-approved but infrequently used longer-horizon option for selected patients with chronic, highly treatment-resistant depression, whereas deep brain stimulation remains investigational or highly specialized in many settings. Neither should be interpreted as a routine early-line intervention. Future work should prioritize standardized definitions of treatment resistance, biomarker-guided targeting, maintenance algorithms, patient-reported outcomes, access equity, and long-term device stewardship. Neuromodulation is a clinically important therapeutic domain for treatment-resistant depression, ranging from established non-invasive treatments to emerging personalized circuit-based interventions. The most reproducible clinical support currently favors electroconvulsive therapy for urgent or severe depression and repetitive transcranial magnetic stimulation as an evidence-based outpatient option after inadequate pharmacotherapy response. Intermittent theta-burst stimulation (iTBS) can improve treatment feasibility through shorter sessions, whereas accelerated delivery of iTBS may shorten the overall treatment course but remains resource-intensive and insufficiently standardized for broad routine dissemination. Vagus nerve stimulation is a regulatory-approved but infrequently used longer-horizon option for selected patients with chronic, highly treatment-resistant depression, whereas deep brain stimulation remains investigational or highly specialized in many settings. Neither should be interpreted as a routine early-line intervention. Future work should prioritize standardized definitions of treatment resistance, biomarker-guided targeting, maintenance algorithms, patient-reported outcomes, access equity, and long-term device stewardship.