Dim Nocturnal Illumination and Plasticity of Circadian Entrainment

在人类和其他哺乳动物中，行为和生理功能的显著日常变化是由内源性神经时钟产生的，内源性神经时钟通过从视网膜到大脑的直接和间接神经投射与光环境同步。先前的研究表明，明亮的光线对于重置生物钟的相位是必要的，并且已经在视网膜中识别出了对光具有匹配敏感性的细胞。 目前的项目探讨了非常昏暗的光（强度低于昏暗的月光）对昼夜节律系统的新作用。 与预期相反，初步研究表明，昏暗的夜间照明导致昼夜节律功能发生显着变化：在其存在下，动物更容易适应日照长度的季节性变化;它们更成功地将其节律带入非24小时天，并将其昼夜节律重组为双峰24小时光：暗：光：暗周期下的多个组成部分。 在一系列的行为研究中，该项目探讨了昏暗光线通过改变昼夜节律振荡器组件之间的耦合或相互作用来发挥其作用的假设。 此外，研究人员还检查了昏暗光线的波长和强度要求，以评估介导其影响的视网膜光感受器。 最后，这些影响进行了检查，在动物的丘脑通过中脑视觉投射上升到昼夜节律起搏器的膝状体间叶病变。 这些研究可能为快速操纵人类昼夜节律提供了新的途径。这些发现可能对优化人类在轮班工作、跨子午线和太空旅行以及其他情况下的表现具有价值。

In humans and other mammals, marked daily variations in behavioral and physiological function are generated by endogenous neural clocks, which are synchronized with the light environment through both direct and indirect neural projections from the retina to the brain. Previous work has shown that bright light is necessary to reset the phase of circadian clocks, and cells with matching sensitivity to light have been identified in the retina. The present project explores novel actions of very dim light (less intense than dim moonlight) on the circadian system. Counter to expectations, preliminary studies show that dim nocturnal illumination results in marked changes in circadian function: in its presence, animals more readily adjust to seasonal changes in daylength; they entrain their rhythms more successfully to non 24-h days and they reorganize their circadian rhythms into multiple components under bimodal 24-h light:dark:light:dark cycles. In a series of behavioral studies, this project explores the hypothesis that dim light exerts its effects by altering the coupling, or interactions, between component circadian oscillators. Further, the investigators examine the wavelength and intensity requirements of dim light to assess the retinal photoreceptors that mediate its effects. Finally, these effects are examined in animals with lesions of the intergeniculate leaflet of the thalamus through which midbrain visual projections ascend to the circadian pacemaker. These studies may suggest new avenues for rapid manipulation of human circadian rhythms. These findings may be of value in optimizing human performance during shift-work, in trans-meridian and space travel, and in other contexts.