The abrupt shift to slower frequencies after arousal from sleep in healthy young adults

Abstract

Study objectives: Postarousal hypersynchrony (PAH) is an atypical arousal pattern in children's electroencephalography. PAH is an abrupt shift to slower frequencies in arousal-related responses, appearing as slow-wave clusters. In contrast, the prevalence of PAH in healthy young adults is still unknown. Here, we examined the prevalence and characteristics of PAH in healthy young participants.

Methods: Thirty healthy young participants underwent 1 night of polysomnography (13 females, 22.8 ± 2.0 years [mean ± standard deviation]). We examined the prevalence of PAH as a function of sleep stage, sleep cycle, and time course (the first or the second half). The correlation between PAH and sleep variables was examined. The percent of total sleep time in the N3 stage (%N3) was compared for each sleep cycle and time course.

Results: Twenty-eight out of 30 participants exhibited PAH (4.6 ± 4.8 times per night). PAH increased significantly during the first sleep cycle and the first half-sleep period. It was observed only in nonrapid eye movement and not in rapid eye movement sleep. The number of PAHs correlated with the number of arousals and arousal indices. The %N3 increased in the first half-sleep and the first sleep cycle.

Conclusions: PAH was relatively common in healthy young participants. Since PAH occurred in a state with a high prevalence of %N3, the first sleep cycle, or the first half-sleep, we suggest that PAH may be affected by the sleep homeostasis process. Since PAH occurred only in non-rapid eye movement sleep and correlated with arousal increment, it may have the function of suppressing non-rapid eye movement sleep's cortical arousal.

Citation: Suzuki Y, Kawana F, Satoh M, Abe T. The abrupt shift to slower frequencies after arousal from sleep in healthy young adults. J Clin Sleep Med. 2021;17(12):2373-2381.

Keywords: arousal; delta activity; electroencephalogram; sleep.

Figure 1. An example of postarousal hypersynchrony.

(A) A polysomnogram at the 30-second epoch. (B) The polysomnogram extended the 60-second epoch. EMG = electromyogram, LEOG = left electrooculogram, REOG = right electrooculogram.

Figure 2. Frequencies of PAH were modified by each stage’s duration, the first or second half-sleep, and sleep cycle.

(A) Numbers of PAH divided by duration in each sleep stage. (B) PAH activities divided by the first or the second half of total recording time. (C) PAH numbers divided by the duration of each sleep cycle. Boxes show interquartile ranges from 25%–75%. Whiskers indicate the range between maximum and minimum. Data points are plotted with circular dots. *P < .05. PAH = postaraousal hypersynchrony, TRT = total recording time.

Figure 3. PAH ratios were divided by the arousal numbers in each sleep stage, the first or second half-sleep, and sleep cycle.

(A) PAH numbers, corrected by dividing the number of arousals in the sleep stage. The 3 participants who showed no arousals in stage N3 were removed from the statistics. (B) PAH activities divided by the number of arousals in the first and second half of total recording time. (C) PAH numbers modified by the arousal number of each sleep cycle. Boxes show interquartile ranges from 25%–75%. Whiskers indicate the range between maximum and minimum. Data points are plotted with circular dots. *P < .05. PAH = postarousal hypersynchrony, TRT = total recording time.

Figure 4. Number of arousals modified by each sleep stage’s duration, the first or second half-sleep, and sleep cycle.

(A) The number of arousals divided by length in the sleep stage. (B) Arousal activities divided by the first or the second half of the total recording time. (C) Arousal numbers modified by dividing the duration of each sleep cycle. Boxes show interquartile ranges from 25%–75%. Whiskers indicate the range between maximum and minimum. Data points are plotted with circular dots. *P < .05. TRT = total recording time.

Figure 5. Box and whisker plot showing the distribution of delta band EEG power during the postarousal hypersynchrony.

The highest delta EEG frequency power can be observed in F4-M1. Boxes show the interquartile ranges from 25%–75% of the delta band EEG power, and whiskers indicate the range between maximum and minimum. Data points are plotted with circular dots. *P < .05. EEG = electroencephalogram.