Our objective was to investigate the physiological mechanisms involved in the sleep restriction treatment of insomnia. A multiple baseline across subjects design was used. Sleep of five participants suffering from insomnia was assessed throughout the experimentation by sleep diaries and actigraphy. Ten nights of polysomnography were conducted over five occasions. The first two-night assessment served to screen for sleep disorders and to establish a baseline for dependent measures. Three assessments were undertaken across the treatment interval, with the fifth and last one coming at follow-up. Daily cortisol assays were obtained. Sleep restriction therapy was applied in-lab for the first two nights of treatment and was subsequently supervised weekly. Interrupted time series analyses were computed on sleep diary data and showed a significantly decreased wake time, increased sleep efficiency, and decreased total sleep time. Sleepiness at night seems positively related to sleep variables, polysomnography data suggest objective changes mainly for stage 2, and power spectral analysis shows a decrease in beta-1 and -2 powers for the second night of treatment. Cortisol levels seem to be lower during treatment. These preliminary results confirm part of the proposed physiological mechanisms and suggest that sleep restriction contributes to a rapid decrease in hyperarousal insomnia. 1. Introduction Sleep restriction therapy for insomnia was developed by Spielman et al. in 1987 [1]. This behavioral intervention consists of restricting the time spent in bed to correspond to the estimated amount of time spent asleep by the patient [1]. Weekly changes are made to the time spent in bed as a function of the patient’s clinical response. Since this first publication, sleep restriction therapy has been frequently included in cognitive-behavioral therapy for insomnia (CBT-I). Meta-analyses of nonpharmacological treatments of insomnia have shown that sleep restriction can be effective in decreasing sleep-onset latency and greatly increasing sleep efficiency in a relatively short time [2–4]. Another meta-analysis has shown that sleep restriction, applied with other behavioral treatment, benefits sleep of adults and older adults, with the exception of total sleep time [5]. Sleep restriction efficacy is well acknowledged by sleep clinicians and researchers [6, 7] who consider it an essential therapeutic component. Sleep restriction mechanisms are seen as involving physiological and psychological processes of sleep. Despite the effectiveness attributed to sleep restriction,
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