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Center for Nonlinear Studies |
Sleep is essential to maintain the physical condition of the body and probably to consolidate memories and learning. Despite its importance, social pressure often leads to a perception that reducing sleep is advantageous, which causes widespread sleep disorders posing public health issues. In this seminar, we review current sleep studies in clinics and discuss potential interdisciplinary collaborations between Physics and Sleep Medicine. Examples of these collaborations are given below. Ex.1) Sleep is a very active and complex process showing many electrophysiological changes in the brain and other organs (e.g., the heart), which causes frequent sleep and (spontaneous) wake transitions during a nocturnal sleep period. To study these transitions, we propose a new approach, based on a Markov transition matrix that can be determined by analyzing clinical sleep data (e.g., hypnograms). Our approach shows that the statistics of sleep can be constructed via a single Markov process and that durations of all states have modified exponential distributions, in contrast to recent reports of a scale-free form for the wake stage and an exponential form for the sleep stage. Ex. 2) At what point can a subject be said to be really asleep, or what is the moment of the sleep onset? These questions are potentially important for the public, especially for the road safety. To examine the process of the sleep onset quantitatively and explore differences between narcoleptics and controls, we apply dynamic detrended fluctuation analysis to electroencephalograms recorded during multiple sleep latency tests. We find that electrophysiological brain activity is changing rapidly across the onset. The sleep onset durations of narcoleptics is significantly larger than that of controls, which suggests that the wake state of narcolepsy being more susceptible to sleep due to a lower barrier to transitioning to sleep.
Reference:
- Kim et al., Phys. Rev. Lett. 102, 178104 (2009).
- Kim et al., Clin. Neurophysiol. 120, 1245 (2009).
Host: Peter Loxley