Dottorato in PSICOLOGIA E SCIENZA COGNITIVA

Titolo della tesi: Insomnia Disorder: association between EEG spectral features, Sleep State Misperception, and Time Estimation Abilities

One of the most striking features of Insomnia Disorder (ID) patients is their tendency to underestimate the length of sleep periods in favor of overestimating periods of wakefulness during sleep. This phenomenon is referred to as the Sleep State Misperception (SSM). Although its impact is currently neglected in diagnostic manuals, its existence and magnitude has always been well renowned in both clinical and research settings. Although considered an elusive phenomenon, during recent years sleep researchers have advanced several electrophysiological and behavioral hypotheses to explain its occurrence. Specifically, several electroencephalographic (EEG) alterations point towards physiological expression of an enhanced level of awareness during sleep and an impaired cortical synchronization in ID patients that may result in SSM. In spite of this neurophysiological evidence, local EEG underpinnings of the phenomenon in ID are far from being understood, and several researchers are now also oriented in integrating these findings with those concerning cognitive and behavioral activity. Indeed, a cognitive explanation for the SSM in ID considered a possible impairment in the Time Estimation Abilities (TEAs) during sleep and wakefulness. Up to now, studies aimed at investigating topographical EEG dynamics and sleep microstructural changes, as well as cognitive and behavioral impairments that may explain the SSM phenomenon in ID, are still few and present several methodological limitations. In this view, a clear framework of the electrophysiological and behavioral mechanisms underlying SSM is still missing. The present study, through two experiments, aims to explore all aspects (i.e., electrophysiological, cognitive and behavioral) that likely characterized SSM in ID, providing for the first time a unique framework to explain this fascinating phenomenon that appears relevant from both theoretical and clinical standpoints. In the first experiment, starting from the hypothesis that TEAs in wake can be influenced by subjective sleep features and sleep quality, 61 healthy controls (HCs) participants were monitored for one week to collect subjective sleep indices and were tested for the TEAs through a Time Reproduction Task (TRT) ad hoc created. In the second experiment, 16 ID patients and 15 sex- and age-matched HCs underwent a whole night polysomnographic (PSG) recording, followed by the administration of a sleep diary to collect subjective sleep estimates and by the TRT. Correlational analysis showed that in all subjects, the delta/beta ratio was positively correlated with the underestimation of the Total Sleep Time (TST). Moreover, results from the two experiments suggest that the TEAs, both during wake and sleep, seem to depend on the hyperarousal state that pervades the ID during the 24 hours.