K-Complexes in Insomnia Disorder and their role in sleep state misperception and sleep stability

Introduction: The K-Complexes (KCs) are involved in sleep protection and arousal processes during sleep. Therefore, they may have a role in hyperarousal, sleep stability, and sleep state misperception (SSM) in insomnia disorder (ID). Methods: Nineteen ID patients (42.4 ± 12.1 years) and 18 healthy controls (HC; 41.6 ± 11.9 years) underwent a night of home-polysomnography followed by morning sleep diary. First, midline KC density, amplitude, and area under the curve were detected to assess their relationship with total sleep time (TST) misperception. Then, we applied a Markov chain analysis to assess the sleep stage transition probability from N2 sleep epochs with low (lKC) and high KC (hKC) density. Results: A reduced anterior KC morphology in ID patients compared to HCs was associated with TST underestimation. The probability of transitioning from N2-hKC to N3 was grater than the probability of transitioning to N1/wakefulness in both groups. ID patients showed greater probability of transitioning from N2 to wakefulness, and lower probability of transitioning from N2-hKC to N3 during the first sleep cycle. Conclusion: These findings suggest a KC morphological alteration in ID associated with SSM, and a difficulty of ID patients to reach deep sleep also in presence of hKC density.