The effect of arousals during sleep onset on estimates of sleep onset latency

It is well established that insomniacs overestimate sleep-onset latency. Fu rthermore, there is evidence that brief arousals from sleep may occur more frequently in insomnia. This study examined the hypothesis that brief arous als from sleep influence the perception of sleep-onset latency. An average of four sleep onsets was obtained from each of 20 normal subjects on each o f two nonconsecutive, counterbalanced, experimental nights. The experimenta l nights consisted of a control night (control condition) and a condition i n which a moderate respiratory load was applied to increase the frequency o f microarousals during sleep onset (mask condition). Subjective estimation of sleep-onset latency and indices of sleep quality were assessed by self-r eport inventory. Objective measures of sleep-onset latency and microarousal s were assessed using polysomnography. Results showed that sleep-onset late ncy estimates were longer in the mask condition than in the control conditi on, an effect not reflected in objective sleep-stage scoring of sleep-onset latency. Furthermore, an increase in the frequency of brief arousals from sleep was detected in the mask condition, and this is a possible source for the sleep-onset latency increase perceived by the subjects. Findings are c onsistent with the concept of a physiological basis for sleep misperception in insomnia.