Abstract :
[en] Insomnia and depression frequently co-occur and mutually reinforce one another. However, the psychological processes associated with this comorbidity remain poorly understood. Using a hybrid network approach, this study examined the organization of clinically significant insomnia–depression comorbidity and the role of four key transdiagnostic psychological processes within this network: rumination, worry, behavioral avoidance, and behavioral inertia.
A total of 702 adults meeting validated clinical cut-offs for both insomnia (ISI > 10) and depression (PHQ-9 > 9) were drawn from a larger community sample. The network included insomnia symptoms, depressive symptoms (excluding the sleep item), rumination, worry, behavioral avoidance, and behavioral inertia. Networks were estimated using EBICglasso, and centrality and bridge centrality indices were calculated.
Suicidal ideation, depressed mood, and fatigue/loss of energy emerged as the most central symptoms in the network. Overall, insomnia and depressive symptoms were more strongly connected within their respective domains than across domains, with relatively few connections between the two. Among these cross-domain connections, fatigue/loss of energy emerged as the strongest bridge symptom linking insomnia and depression. Contrary to expectations, transdiagnostic psychological processes were not the most central nodes in the network, with symptoms generally occupying more central positions. Overall, these processes showed stronger connections with depressive symptoms than with insomnia symptoms, although their patterns of association varied across processes and individual symptoms.
These findings highlight several potential clinical implications. First, the prominent role of fatigue/loss of energy, both as a central symptom and as the strongest bridge between insomnia and depression, suggests that fatigue may deserve particular attention in comorbid presentations. Second, the relatively limited connections between insomnia and depressive symptoms suggest that improvement in one domain may not necessarily translate into improvement in the other, supporting the relevance of addressing both sleep and depressive symptoms in treatment. Finally, transdiagnostic psychological processes appeared to be more closely related to depressive than to insomnia symptoms, with different processes showing specific associations with particular symptoms. Their clinical relevance may therefore vary across patients, supporting an individualized, process-based approach in which case formulation helps identify the most relevant treatment targets. Longitudinal and intervention studies are needed to determine whether these cross-sectional associations reflect mechanisms of change.
