Kharchenko Vasili, Rozman Michael, Putilov Arcady A, Zhdanova Irina V
Department of Physics, University of Connecticut, Storrs, CT 06269, United States.
Laboratory of Sleep/Wake Neurobiology, Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences, 117865 Moscow, Russia.
Sleep Adv. 2025 Jul 21;6(3):zpaf046. doi: 10.1093/sleepadvances/zpaf046. eCollection 2025.
The mismatch between rising sleep need and the fluctuating ability to fall asleep underlies insomnia-the most common sleep disorder-yet remains poorly understood. While sleep need increases steadily with time awake, sleep propensity-the likelihood of transitioning from wake to sleep-follows a bimodal pattern, peaking in the mid-afternoon, dipping in the evening, and rising again near bedtime. Building on our previously developed wave model of sleep dynamics, we extend this homeostatic framework to the waking period and show that it predicts the observed bimodal sleep propensity curve. This pattern emerges from two interacting factors: wake-state instability, which increases exponentially across the day, and interaction strength between states, which follows a biphasic trajectory. Together, they produce a daily profile of sleep propensity that closely aligns with experimental data. Notably, the empirical curve demonstrates a deeper evening dip than the model alone predicts-reflecting the known circadian modulation of sleep propensity. The model reveals that the mid-afternoon peak reflects maximal interaction at the homeostatic equilibrium threshold, while the evening dip results from minimal coupling between sleep and wake states, counteracting high instability. A late-day rise in both factors facilitates sleep onset at bedtime and beyond. Experimental data from sleep deprivation further support these predictions. This work provides a mechanistic foundation for understanding daily sleep propensity and may inform strategies to improve sleep and performance in both health and disease.
睡眠需求不断增加与入睡能力波动之间的不匹配是失眠（最常见的睡眠障碍）的根本原因，但人们对此仍知之甚少。虽然睡眠需求会随着清醒时间的增加而稳步上升，但睡眠倾向（即从清醒状态转变为睡眠状态的可能性）呈现双峰模式，在下午中段达到峰值，在晚上下降，临近就寝时间又再次上升。基于我们之前开发的睡眠动力学波动模型，我们将这个稳态框架扩展到清醒期，并表明它能够预测观察到的双峰睡眠倾向曲线。这种模式源于两个相互作用的因素：清醒状态的不稳定性，它在一天中呈指数级增加；以及不同状态之间的相互作用强度，它遵循双相轨迹。这两个因素共同产生了与实验数据紧密吻合的每日睡眠倾向概况。值得注意的是，经验曲线显示晚上的下降幅度比仅由模型预测的更深，这反映了已知的睡眠倾向昼夜节律调节。该模型表明，下午中段的峰值反映了在稳态平衡阈值处的最大相互作用；而晚上的下降则是由于睡眠和清醒状态之间的耦合最小，抵消了高度的不稳定性。这两个因素在一天后期的上升促进了就寝时间及之后的睡眠开始。睡眠剥夺的实验数据进一步支持了这些预测。这项工作为理解每日睡眠倾向提供了一个机制基础，并可能为改善健康和疾病状态下的睡眠及表现的策略提供参考。
