Oscillatory patterns in the electroencephalogram at sleep onset

Abstract

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.

The electroencephalographic features of the sleep onset process and their experimental manipulation with sleep deprivation and transcranial electrical stimulation protocols

“…EEG power spectra have been widely assessed during the SO process (for a review, see Gorgoni et al, 2019a), albeit only a few studies described its topographical pattern with a satisfactory spatial resolution (Marzano et al, 2013;Gorgoni et al, 2019b); b) Rhythmic oscillatory activity: the assessment of the EEG power does not necessarily highlight genuine rhythmic oscillations in the specific frequency range of interest. On the other hand, the SO process mainly involves modifications in oscillatory activity, and it has been described with the Better OSCillation (BOSC) detection method (Marzano et al, 2013;Gorgoni et al, 2019b), that considers the functional form of a background non-rhythmic portion of the signal to detect deviations from the background (Caplan et al, 2001), or assessing the event ratio, that is the sum of the duration of oscillatory events divided by the total time in a given window (Achermann et al, 2019). c) Cortical sources: it consists of the assessment of the strength and distribution of the intracranial sources of scalp electric potential differences.…”

“…Gennaro et al, 2001aGennaro et al, , 2001bMarzano et al, 2013;Siclari et al, 2014;Tanaka et al, 2000;Werth et al, 1997) Global increase (Marzano et al, 2013;Siclari et al, 2014;Wright et al, 2015), with an occipital peak (Marzano et al, 2013) Gradual pre-SO reduction of the occipital alpha, followed by a post-SO increase of fronto-central alpha (De Gennaro et al, 2001b;Hasan and Broughton, 1994;Marzano et al, 2013;Tanaka et al, 1997) Post-SO increase with a centroparietal predominance (De Gennaro et al, 2001a, 2001bMarzano et al, 2013;Siclari et al, 2014) Global reduction of the beta (De Gennaro et al, 2001a, 2001bMarzano et al, 2013;Merica et al, 1991;Merica and Gaillard, 1992) and gamma activity (Siclari et al, 2014) REC Compared to BSL, global increase of the post-vs. pre-SO ratio Compared to BSL, global increase of the post-vs. pre-SO ratio Compared to BSL, increased post-vs. pre-SO ratio, global at 8−9 Hz and fronto-central at 10 Hz Compared to BSL, absence of quantitative differences Compared to BSL, absence of quantitative differences in the beta range Gamma activity not assessed Oscillatory activity BSL Global increase, that reaches its maximum in the midline central area in the frequency peak (Marzano et al, 2013) In the frequency peak, strong increase in the temporo-parietal regions (Marzano et al, 2013). Appearance of "fast" delta/theta oscillatory events (1.5−7 Hz) in stage 1 with highest central incidence, that reach their maximum event-ratio immediately after SO and then decrease with time (Achermann et al, 2019) Transition from a posterior to an anterior predominance (Marzano et al, 2013;…”

“…Global frequency reduction with an antero-posterior gradient (Achermann et al, 2019) Gradual decrease in the beta activity with a maximum in temporofrontal areas. Post-SO decline in the oscillatory peak in the lateral frontal areas and right occipital region (Marzano et al, 2013).…”

Changes during the sleep onset process on EEG activity and the components of attention

“…Other studies have documented changes in EEG activity and attention on longer periods before and after the sleep onset. These studies report that right before the sleep onset there is an appearance of slow frequencies (theta and delta), and a reduction of beta activity compared to a state of wakefulness 37 . One of these studies also reports that the capacity to respond to simple stimuli decreases a lot in the minute before sleep onset 38 .…”

Low Frequency Transcranial Alternating Current Stimulation Accelerates Sleep Onset Process

“…The curve of energy gradual change from time-frequency analysis was used to distinguish the alpha wave, spindle wave (mainly sigma frequency band) and low frequency component (mainly 1-7Hz frequency band) of EEG, and the dynamic change of EEG signal was showed (see Fig. 2-3) [24].The wavelet time-frequency representation reflect stimulation effect. Meanwhile, it is worth noting that the wavelet time- frequency representation of the control group is consistent with that of Prerau, M. et al [25].…”