Sleep onset misperception in insomnia disorder: a pilot study with methodological implications

Objective/Introduction: Subjects with insomnia frequently report a discrepancy between objectively and subjectively defined sleep onset. The aim of this study was to investigate which factors may influence sleep onset misperception in insomnia patients by assessing the presence of possible links between the degree of misperception and objectively detected sleep variables. Methods: 16 patients with insomnia disorder were recruited. They underwent a full night polysomnographic recording and completed a comprehensive sleep diary. The values of objective and subjective sleep onset latencies were recorded and a sleep onset misperception index was calculated. A series of sleep parameters were chosen on the basis of a review of the literature and were tested. These variables were: latency to N1, latency to N2, latency to N3, latency to the first K-complex and percentage of clearly detectable and stereotypical alpha rhythm during subjectively defined sleep onset. Moreover, a model proposed by Hermans and collaborators in 2019 was also tested. This model postulated the existence of a variable called L, which express the duration of an uninterrupted sleep fragment at sleep onset in order to be perceived as sleep. Finally, a colour-graded representation depicting the presence of sleep/wake states during subjective sleep onset was performed. Results: A positive correlation between sleep onset misperception and the percentage of stereotypical alpha rhythm was found (rhospearman = 0.564, p = 0.025). Moreover, both latency to the first epoch of N2 and to the first K-complex showed a tendency towards statistical significance in correlation with sleep onset misperception (rhospearman = 0.380, p = 0.065; rhospearman = 0.403, p = 0.057, respectively). Moreover, by dividing the sample in patients with a sleep onset misperception 10 min, we found that patients with more than 10 min of discrepancy showed a significant increase in percentage of alpha rhythm during subjective sleep onset (16,5% vs 2,6%, p = 0.009). No significant association was found between L and the degree of sleep onset misperception. Conclusions: These data suggest the importance of further investigating the link between misperception, alpha rhythm, and hyperarousal levels and once again the need to redefine the construct of sleep onset latency both in research and in clinical contexts. Disclosure: N