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Oscillatory patterns in the electroencephalogram at sleep onset

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Achermann Peter, Rusterholz Thomas, Stucky Benjamin, Olbrich Eckehard,
Project Sleep onset and other state transitions: insights from quantitative EEG analysis
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Original article (peer-reviewed)

Journal Sleep
Volume (Issue) 42(8)
Page(s) 1 - 12
Title of proceedings Sleep
DOI 10.1093/sleep/zsz096

Open Access

Type of Open Access Green OA Embargo (Freely available via Repository after an embargo)


Falling asleep is a gradually unfolding process. We investigated the role of various oscillatory activities including sleep spindles and alpha and delta oscillations at sleep onset (SO) by automatically detecting oscillatory events. We used two datasets of healthy young males, eight with four baseline recordings, and eight with a baseline and recovery sleep after 40 h of sustained wakefulness. We analyzed the 2-min interval before SO (stage 2) and the five consecutive 2-min intervals after SO. The incidence of delta/theta events reached its maximum in the first 2-min episode after SO, while the frequency of them was continuously decreasing from stage 1 onwards, continuing over SO and further into deeper sleep. Interestingly, this decrease of the frequencies of the oscillations were not affected by increased sleep pressure, in contrast to the incidence which increased. We observed an increasing number of alpha events after SO, predominantly frontally, with their prevalence varying strongly across individuals. Sleep spindles started to occur after SO, with first an increasing then a decreasing incidence and a continuous decrease in their frequency. Again, the frequency of the spindles was not altered after sleep deprivation. Oscillatory events revealed derivation dependent aspects. However, these regional aspects were not specific of the process of SO but rather reflect a general sleep related phenomenon. No individual traits of SO features (incidence and frequency of oscillations) and their dynamics were observed. Delta/theta events are important features for the analysis of SO in addition to slow waves.