Chronic insomnia neurophysiological aspects: PSG and resting-state fMRI data

INTRODUCTION. Chronic insomnia is a common sleep disorder characterized by difficulty initiating or maintaining sleep, as well as early morning awakenings. Despite its clinical significance, diagnosis remains challenging due to discrepancies between subjective complaints and objective sleep parameters. In addition to polysomnography (PSG), resting-state functional magnetic resonance imaging (rs-fMRI) has recently gained increasing attention allowing it to assess neurophysiological changes associated with insomnia. A comprehensive assessment of chronic insomnia pathophysiology including PSG, rs-fMRI, and validated sleep questionnaires may become the key to developing personalized approach to diagnosis and treatment.

AIM. The study aims to conduct a comprehensive assessment of objective sleep characteristics and brain functional activity in patients with chronic insomnia using polysomnography, resting-state functional MRI, and validated sleep questionnaires, in order to identify neurophysiological features of the disorder and clarify subjective complaints and objective findings correlation.

MATERIALS AND METHODS. Current study included 47 patients diagnosed with chronic insomnia after a somnologist appointment at Almazov National Medical Research Centre (St. Petersburg). All participants underwent single-night PSG using Embla N7000 (Natus, USA) and SOMNO HD (SOMNOmedics, Germany) devices, with scoring performed according to AASM 2.5 criteria. Structural and functional MRI scans were performed at 3.0 T. Functional data was analyzed using MathLab R2024b and CONN toolbox.

RESULTS. Patients with chronic insomnia demonstrated significantly higher scores on ISI (Insomnia Severity Index), PSQI (Pittsburgh Sleep Quality Index), and ESS (Epworth Sleepiness Scale) compared to the control group (p<0.001), indicating pronounced subjective sleep complaints. However, contrary to expectations, polysomnographic data revealed better sleep parameters among insomnia patients, including higher sleep efficiency and longer total sleep duration, along with shorter sleep latency, fewer microarousals, and reduced wake time after sleep onset (p<0.05). These findings suggest sleep-state misperception (paradoxical insomnia) in a subset of patients. Resting-state fMRI revealed increased connectivity within the default mode network and heightened sensorimotor cortex activity in the evening, along with enhanced activation of language and executive networks in the morning. These findings reflect dysregulation of sleep-wake transitions and underscore the need for a comprehensive approach to the diagnosis of chronic sleep disorders.

CONCLUSION. The study findings indicate a discrepancy between subjective complaints and objective sleep parameters in chronic insomnia, suggesting the presence of sleep-state misperception (paradoxical insomnia). Altered brain functional activity supports chronic hyperarousal and highlights the importance of a comprehensive approach to diagnosis and treatment of this disorder.

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