Nakamura K
First Department of Physiology, Hokkaido University School of Medicine, Sapporo, Japan.
Hokkaido Igaku Zasshi. 1996 May;71(3):403-22.
The present study was performed in order to have better understanding of the human circadian system. Two hypotheses concerning with the human circadian system have been advanced. One is a two self-sustained oscillator hypothesis, and the other is a two process hypothesis. Both hypotheses are based on a phenomenon called internal desynchronization. A major difference between the two hypothesis is that sleep or wakefulness does not affect the circadian oscillation in the two process hypothesis, while a mutual interaction between sleep (wakefulness) and the circadian oscillation is not excluded in the two oscillator hypothesis. On the other hand, social sues such as a sleep-wake schedule and regular contact with others have been considered as a major time cues (zeitgeber) for the human circadian rhythm. However, lights brighter than 5,000 lux was recently demonstrated to be capable of resetting the human circadian rhythm, and it is now a matter of debate whether the resetting effect of social cues is due to the light-dark cycle inevitably associated with a sleep-wake schedule. In the present study, the effects of forced sleep-wake schedules on the circadian rhythm in plasma melatonin and rectal temperature were examined in subjects under temporal isolation, which are not explained by the two process hypothesis. As a result, the forced sleep-wake schedule of 24.0-hour period in dim light condition (below 200 lux) entrained the circadian rhythms in 3 out of 8 subjects. The forced schedule in extremely dim light condition (below 5 lux) was also capable of entraining the circadian rhythm. On the other hand, the forced schedule of 23.5-hour period showed no entrainability. It is concluded that the non-photic entrainment is operating in the human circadian clock, which supports the two self-sustained oscillator hypothesis.
进行本研究是为了更好地了解人类昼夜节律系统。关于人类昼夜节律系统，已经提出了两种假说。一种是双自维持振荡器假说，另一种是双过程假说。这两种假说均基于一种称为内源性失同步的现象。这两种假说的一个主要区别在于，在双过程假说中，睡眠或觉醒不影响昼夜节律振荡，而在双振荡器假说中，睡眠（觉醒）与昼夜节律振荡之间的相互作用并未被排除。另一方面，诸如睡眠-觉醒时间表以及与他人的定期接触等社会因素已被视为人类昼夜节律的主要时间线索（授时因子）。然而，最近有研究表明，亮度超过5000勒克斯的光线能够重置人类昼夜节律，社会线索的重置效应是否归因于与睡眠-觉醒时间表不可避免相关的明暗周期，目前仍存在争议。在本研究中，对处于时间隔离状态的受试者施加强制睡眠-觉醒时间表，观察其对血浆褪黑素和直肠温度昼夜节律的影响，而这是双过程假说无法解释的。结果显示，在昏暗灯光条件（低于200勒克斯）下的24.0小时强制睡眠-觉醒时间表使8名受试者中的3名的昼夜节律得以同步。在极暗灯光条件（低于5勒克斯）下的强制时间表也能够使昼夜节律同步。另一方面，23.5小时的强制时间表则无法实现同步。结论是，非光性同步作用存在于人类生物钟中，这支持了双自维持振荡器假说。
