School of Physics, University of Sydney, New South Wales 2006, Australia.
J Theor Biol. 2012 Dec 7;314:109-19. doi: 10.1016/j.jtbi.2012.08.031. Epub 2012 Sep 1.
Unihemispheric sleep has been observed in numerous species, including birds and aquatic mammals. While knowledge of its functional role has been improved in recent years, the physiological mechanisms that generate this behavior remain poorly understood. Here, unihemispheric sleep is simulated using a physiologically based quantitative model of the mammalian ascending arousal system. The model includes mutual inhibition between wake-promoting monoaminergic nuclei (MA) and sleep-promoting ventrolateral preoptic nuclei (VLPO), driven by circadian and homeostatic drives as well as cholinergic and orexinergic input to MA. The model is extended here to incorporate two distinct hemispheres and their interconnections. It is postulated that inhibitory connections between VLPO nuclei in opposite hemispheres are responsible for unihemispheric sleep, and it is shown that contralateral inhibitory connections promote unihemispheric sleep while ipsilateral inhibitory connections promote bihemispheric sleep. The frequency of alternating unihemispheric sleep bouts is chiefly determined by sleep homeostasis and its corresponding time constant. It is shown that the model reproduces dolphin sleep, and that the sleep regimes of humans, cetaceans, and fur seals, the latter both terrestrially and in a marine environment, require only modest changes in contralateral connection strength and homeostatic time constant. It is further demonstrated that fur seals can potentially switch between their terrestrial bihemispheric and aquatic unihemispheric sleep patterns by varying just the contralateral connection strength. These results provide experimentally testable predictions regarding the differences between species that sleep bihemispherically and unihemispherically.
已在包括鸟类和水生哺乳动物在内的许多物种中观察到单侧睡眠。尽管近年来人们对其功能作用的了解有所提高，但产生这种行为的生理机制仍知之甚少。在这里，使用哺乳动物上行觉醒系统的基于生理学的定量模型模拟单侧睡眠。该模型包括由昼夜节律和稳态驱动以及胆碱能和食欲素能输入到 MA 的促醒单胺能核（MA）和促眠腹外侧视前核（VLPO）之间的相互抑制。这里将该模型扩展到包含两个不同的半球及其连接。假设相反半球的 VLPO 核之间的抑制性连接负责单侧睡眠，并且表明对侧抑制性连接促进单侧睡眠，而同侧抑制性连接促进双侧睡眠。交替单侧睡眠发作的频率主要由睡眠稳态及其相应的时间常数决定。结果表明，该模型再现了海豚的睡眠，并且人类、鲸目动物和海豹的睡眠模式，后者在陆地和海洋环境中，仅需要对侧连接强度和稳态时间常数进行适度改变。进一步表明，海豹可以通过仅改变对侧连接强度在其陆地双侧睡眠和水生单侧睡眠模式之间切换。这些结果提供了可通过实验检验的预测，这些预测涉及双侧睡眠和单侧睡眠物种之间的差异。
