Resting-State Functional Connectivity Alterations in Insomnia Disorder: A Systematic Review of Studies Published from 2020 to July 2025
: Insomnia disorder is increasingly linked to abnormalities in resting-state functional connectivity (rsFC). We systematically synthesized rs-fMRI studies published from January 2020 to July 2025 to characterize disorder-related connectivity patterns and methodological limitations. Twenty-four study reports met the eligibility criteria; reported sample sizes summed to 1,229 participants with insomnia disorder and 1,077 healthy controls, although some cohorts may overlap across publications. Alterations involved the default mode, salience, executive-control, emotion, and sensorimotor systems and sleep–wake regulatory hubs, including the thalamus and hypothalamus. The overall pattern is compatible with hyperarousal, but both increased and decreased connectivity were reported; diagnostic definitions, sex, symptom severity and duration, medication exposure, acquisition conditions, and seed-based versus data-driven analyses may moderate direction and magnitude. A formal study-level appraisal with the JBI analytical cross-sectional checklist identified predominantly low risk or some concerns, most often related to confounding control. Because all included comparisons were cross-sectional, rsFC alterations cannot be interpreted as causes rather than consequences or correlates of insomnia. Methodological heterogeneity precluded quantitative pooling. Standardized phenotyping, medication control, acquisition and preprocessing, preregis-tered longitudinal studies, and external validation are required before connectivity markers can be used clinically