The effects of presleep stress on sleep-onset insomnia.

This study examined the effects of presleep cognitive stress on insomniac and noninsomniac subjects. Ten sleep-onset insomniacs and 11 noninsomniacs spent five nights in a sleep laboratory. They slept undisturbed on the first three nights but were exposed to brief cognitive stressors before sleep-onset on the fourth and fifth nights. Significant between-group differences were found in their responses to the cognitive stressors on self-report but not objective measures of sleep-onset latency. Noninsomniac subjects evidenced an increase in sleep-onset latency and insomniac subjects evidenced a decrease in sleep-onset latency on stress nights. Insomniac subjects demonstrated a significantly higher mean heart-rate response before and after the stressors. A variable expressing the relationship between objective and subjective measures of sleep-onset latency (pseudoidiopathic dimension) for each subject was not significantly related to the subjects response to stress. The results of this study were inconsistent with the hypothesized role of presleep stress in sleep-onset insomnia but were consistent with other studies in indicating higher levels of physiological arousal for insomniac and for noninsomniac subjects. The implications of these findings for a cognitive theory of insomnia etiology are discussed.