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Published on: August 2, 2017
Revisiting spontaneous internal desynchrony using a quantitative model of sleep physiology
Andrew J K Phillips1, Charles A Czeisler, Elizabeth B Klerman
1Division of Sleep Medicine, Brigham & Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. ajphillips@partners.org
Human circadian rhythms can desynchronize due to behavioral influences, leading to altered sleep patterns. This study models how orexinergic signals and weakened circadian input cause internal desynchrony and bicircadian rhythms.
Area of Science:
- Neuroscience
- Chronobiology
- Computational Biology
Background:
- Human circadian rhythms typically entrain to a 24-hour day.
- Free-running conditions can reveal intrinsic circadian periods and lead to phenomena like internal desynchrony.
- Previous models (e.g., Kronauer et al., 1982) reproduced these phenomena but lacked a clear physiological basis.
Purpose of the Study:
- To investigate the physiological mechanisms underlying spontaneous internal desynchrony of human circadian rhythms.
- To model how changes in specific neural pathways could explain observed alterations in circadian and sleep/wake cycles.
- To explore the role of behavioral feedback in circadian rhythm regulation.
Main Methods:
- Utilized a physiologically based computational model of hypothalamic and brain stem nuclei.
- Simulated changes in orexinergic (Orx) wake signaling pathways.
- Modeled attenuation of circadian input to key hypothalamic nuclei.
Main Results:
- The model reproduced key experimental observations: lengthened circadian periods, spontaneous internal desynchrony, and bicircadian sleep/wake cycles.
- Increased orexinergic tone explained delayed sleep and period lengthening.
- Weakened circadian input to the ventrolateral preoptic nucleus induced desynchrony, with cycle period dependent on orexinergic up-regulation.
- Sleep homeostasis drove sleep/wake cycles during desynchrony, while sleep bout length remained phase-dependent.
Conclusions:
- Internal desynchrony can arise from altered orexinergic wake promotion and reduced circadian signal strength.
- Behavioral factors, such as the removal of daily schedules, may influence orexinergic tone and contribute to desynchrony.
- The model successfully predicts transitions to bicircadian rhythms and the phase-dependence of sleep bout length.
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