Microsleep episodes in the borderland between wakefulness and sleep

Hertig-Godeschalk, Anneke; Skorucak, Jelena; Malafeev, Alexander; Achermann, Peter; Mathis, Johannes; Schreier, David R · 2019 · Crossref

DOI: 10.1093/sleep/zsz163

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Summary

This study addresses the lack of standardized scoring criteria for the wake-sleep transition zone, a "borderland" containing microsleep episodes (MSEs) that are clinically relevant for diagnosing sleepiness and assessing fitness to drive. Current American Academy of Sleep Medicine (AASM) guidelines neglect this zone, using 30-second epochs that fail to capture rapid fluctuations between wakefulness and sleep. The authors aimed to develop the Bern continuous and high-resolution wake-sleep (BERN) criteria to visually score MSEs in the electroencephalogram (EEG) with high temporal resolution, specifically within the Maintenance of Wakefulness Test (MWT). The researchers retrospectively analyzed MWT recordings from 76 patients with suspected excessive daytime sleepiness. They scored one trial per patient using both standard AASM criteria and the newly developed BERN criteria, which defined MSEs as lasting 1–15 seconds based on occipital EEG patterns and ≥80% eyelid closure. To objectify these visual scores, the team performed quantitative spectral analysis of the EEG and electrooculography (EOG), deriving features such as power in delta, theta, alpha, and beta bands, and the ratio of theta to alpha-plus-beta activity. Inter-scorer reliability was assessed using Cohen’s kappa. The results demonstrated that the BERN criteria effectively identified MSEs with substantial inter-scorer reliability (kappa = 0.75). The latency to the first MSE was significantly shorter than the AASM-defined sleep latency. In 55% of patients, MSEs occurred even when sleep was not reached within the 40-minute trial. Among those who did fall asleep, 90% experienced at least one preceding MSE, with sleep typically occurring six minutes after the first MSE. Quantitative analysis confirmed that MSEs were characterized by diminished alpha and beta activity, increased theta activity, and a lack of eye movements. Patients with shorter intervals between the first MSE and sleep onset spent a greater relative proportion of time in MSEs. Series of MSEs were more frequent in patients with shorter sleep latencies, whereas isolated MSEs were more common in those who remained awake. The study concludes that the BERN criteria provide a valuable tool for analyzing the wake-sleep transition zone, offering higher sensitivity than AASM standards. By capturing early signs of sleepiness through high-resolution EEG scoring, this method improves the assessment of sleep pressure and may enhance differential diagnosis and safety evaluations, such as fitness to drive. The findings suggest that MSEs are a robust predictor of impending sleep and that the transition from wakefulness to sleep is often a prolonged, fluctuating process rather than an abrupt event.

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Topics

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• microsleep
• drowsiness
• drowsiness detection algorithms