Using evoked anxiety to clarify the psychophysiological features of difficulty falling asleep in napping conditions ofyoung adults

摘要

Bedroom climate, as well as psychological state at bedtime, has been known to crucially influence quality of sleep. Evaluations of sleep onset insomnia by polysomnography with the standard criteria by Rechtschaffen and Kales often indicate that insomnia marked by difficulty falling asleep shares the same structure as healthy, normal sleep. The purpose of this study was to investigate whether subjective feelings of difficulty falling asleep were accompanied by objective features in sleep stage. Objective criteria established for the nine electroencephalogram (EEG) stages and autonomic nervous activity could confirm subjective complaints of difficulty falling asleep in response to anxiety evoked before a 30-minute nap. Participants were 20 healthy students (11males and 9 females, mean age = 21.0 士1.76 years), who were randomly assigned to control or anxiety-evoked groups. The anxiety-evoked group received anxiety-evoking instructions about a speech task before a nap, whereas the control group received no such instructions. The anxiety-evoked group exhibited greater anxiety after the speech task and more negative responses on the Sleep Onset Questionnaire than did the control group. The latencies of each EEG stage from H5 to H8 were significantly longer in the anxiety-evoked group, while the latencies of sleep stages1and 2 did not differ between the groups. Additionally, mean LF/HF ratios (heart rate variability) at the time of each EEG stage's first appearance during the 30-minute nap, indicatingsympathetic nervous activity, were significantly higher in the anxiety-evoked group. These results suggest that using the nine EEG stages (instead of the four sleep stages) and a measure of autonomic nervous activity may verify subjective complaints of difficulty falling asleep due to acute anxiety just before bedtime. The combination of indices used in this study may capture the more minute changes inherent in the sleep-initiation process and contribute to improving our sleep environments.