From Therapeutic Heterogeneity to Precision Neuromodulation: Non-Invasive Brain Stimulation for Chronic Insomnia.

Chronic insomnia is linked to impaired daytime functioning, diminished quality of life, and heightened psychiatric and cardiometabolic risks. While cognitive behavioral therapy for insomnia and pharmacotherapy are well-established treatments, their clinical effectiveness may be constrained by limited accessibility, incomplete response, relapse, adherence challenges, or adverse effects. Non-invasive brain stimulation (NIBS) has therefore attracted increasing interest as a potential adjunctive or alternative intervention because it may modulate cortical excitability, large-scale brain networks, sleep-related oscillations, and autonomic function. This narrative review synthesizes current evidence on repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), and transcutaneous auricular vagus nerve stimulation (taVNS) for chronic insomnia. Particular attention is given to therapeutic heterogeneity across stimulation targets, parameters, treatment schedules, patient phenotypes, and outcome measures. Available studies suggest potential improvements in subjective sleep quality and selected objective sleep parameters; however, the evidence remains limited by small sample sizes, variable sham designs, short follow-up durations, and inconsistent findings across modalities. We further propose a precision neuromodulation framework based on individualized functional targeting, biomarker-informed patient stratification, closed-loop feedback regulation, and integration with behavioral or pharmacological treatment pathways. This review highlights the translational promise of NIBS and outlines methodological priorities needed to move from heterogeneous evidence toward clinically reliable precision neuromodulation.