Abstract
Human and rodent vigilance states have evolutionarily conserved control mechanisms, which suggests that measures of sleep can translate from the laboratory to the clinic. Continuity is an essential aspect of sleep architecture that facilitates the restoration of both body and mind. Current measures of vigilance state continuity do not align well between species and this prevents accurate translation. Throughout this thesis, survival and transition probability analyses were evaluated for their ability to quantify vigilance state continuity in humans and rats. These techniques produced more effective quantification of sleep architecture than metrics such as wake after sleep onset, number of awakenings and average bout lengths. Two methods for defining a bout were first investigated. In both humans and rats, statistical properties of bouts were characterized using different bout-duration thresholds. It was found that bouts are best modelled with distributions that include a time component. Biological relevance of sleep continuity was also investigated in rats, where bouts of NREM sleep as short as 20 seconds reduced the homeostatic pressure, yet awakenings as short as 10 seconds were enough to disrupt the restorative processes of sleep. Short bouts were therefore an important component of sleep architecture and must be considered when evaluating continuity. Continuity metrics were next used to evaluate sleep restriction in rats and circadian rhythmicity in humans. Both homeostatic and circadian influences exerted significant control of NREM sleep continuity, whilst REM continuity was mostly unaffected. Finally, pharmacological agents were tested and their impact on state continuity effectively translated between species. NREM sleep continuity was not altered by the REM sleep inhibition of SSRI’s which differed to the deficits induced by REM sleep restriction. The main contribution of this thesis is to demonstrate that accurate quantification of vigilance state continuity can improve understanding of sleep architecture and the evaluation of pharmacological agents to deliver better patient outcomes.