Functional connectivity changes in insomnia disorder: a systematic review

Insomnia (ID) is the most common sleep disorder; however pathogenetic mechanismsunderlying ID symptoms are not fully understood. Adopting a multifactorial view andconsidering ID a condition that involves interregional neuronal coordination would be usefulto understand the ID pathophysiology. Functional connectivity (FC) may help to shed light onfunctional processes and neural correlates underlying ID symptoms. Despite a growingnumber of studies assessing FC anomalies, insight into ID pathophysiology is stillfragmentary. This systematic review aims to search empirical evidence regarding FC changesin ID during resting-state. Thirty-one studies involving 1052 ID participants met the inclusioncriteria for this review. Results suggested several associations between ID symptoms andimpaired intra- and inter-hemispheric interactions of principal resting-state networks. Overall,evidence supported the hypothesis that a disrupted organization of the brain functionalconnectome characterizes ID, resulting in a decline in sleep, cognition, emotion, and memory.However, the wide methodological heterogeneity between reviewed studies and limitations interms of study protocols and statistical approaches raised from this systematic review, makesit difficult to provide a univocal framework of ID pathophysiology. Future researches in thisfield should lead towards shared and rigorous search designs to ensure solid research evidencein the ID pathophysiology.