Using colour to tell time

动物如何分辨时间？这是一个重要的问题，因为在生理和行为的各个方面驱动日常节奏的内部生物钟必须与外部时间保持一致。多年来，人们一直认为最重要的外部信号是环境照明中的巨大昼夜差异。有大量证据表明，视网膜将有关环境亮度的信息发送到大脑中称为视交叉上核（SCN）的生物钟，并且该信号可以重置时钟相位。然而，我们最近已经证明，这不是光可以用来告诉时间的唯一方式。在整个黄昏，自然光的光谱组成发生了很大的变化，在低太阳角处，波长较短的自然光变得丰富。因此，随着太阳角度的减小，光线逐渐变蓝。我们可以自己感知到这种颜色的变化，事实上，因为它相对不受云的影响，它提供了一个比亮度更可靠的时间指标。现在，使用一系列复杂的视觉刺激，我们已经表明，哺乳动物SCN是敏感的颜色变化，包括颜色的变化，提高了相夹带的小鼠暴露于自然光周期。这些数据首次证明了哺乳动物可以利用颜色来判断时间。我们现在想知道SCN是如何变得对颜色敏感的;时钟对光的反应如何由光的强度和颜色来定义;以及昼夜活动动物的时钟是否也对颜色敏感。 回答这些问题将提供关于这种新发现的感觉生物学成分的基本信息。它也代表了我们需要的关键知识，以确定我们发现的实际重要性。人类和动物的生物钟紊乱（例如轮班工作、衰老和各种疾病）与对精神/身体表现、健康和福祉的一系列负面影响有关。人们已经对现代视觉显示和人造光如何影响时钟产生了浓厚的兴趣。一方面，人们担心夜间太多的光和/或白天太少的自然光（例如对于室内饲养的动物）会影响时钟相位。另一方面，通过改变光的特性，人们可以设计出更好地支持自然节奏的系统。到目前为止，这项工作主要集中在不同光照强度的影响上。它的颜色已经被考虑过，但只有在某些波长更有效地诱导时钟的“亮度”响应的情况下。我们的数据还表明，我们应该考虑它的真实颜色。这里描述的实验代表了确定我们是否以及如何调节颜色以支持人类和家畜适当的昼夜生理的基本步骤。

How do animals tell time of day? This is an important question because internal circadian clocks, which drive daily rhythms in practically every aspect of physiology and behaviour, must be aligned with external time. For many years its been accepted that the most important external signal is the huge day:night difference in ambient illumination. There is a great deal of evidence that the retina sends information about environmental brightness to the circadian clock in a part of the brain called the suprachiasmatic nuclei (SCN) and that this signal can reset clock phase. However, we have recently shown that this is not the only way in which light can be used to tell time. Across twilight there is a big change in the spectral composition of natural light with shorter wavelengths enriched at low solar angles. As a result, light appears progressively bluer as solar angle decreases. We can perceive this change in colour ourselves and, in fact, because it is relatively unaffected by clouds, it provides a more reliable indicator of time across dawn and dusk transitions than does brightness. Now, using a range of sophisticated visual stimuli, we have shown that the mammalian SCN is sensitive to changes in colour and that including changes in colour improves the phase of entrainment of mice exposed to naturalistic light cycles. Those data represent the first demonstration that mammals can use colour to tell time. We now would like to know how the SCN comes to be colour sensitive; how the clock's response to light is defined by its intensity and colour; and whether the clock of diurnal animals is also colour sensitive. Answering these questions will provide basic information about this newly discovered component of sensory biology. It also represents the key knowledge that we need in order to define the practical importance of our discovery. Disruptions to entrainment of the clock (e.g. in shift-work, ageing and various diseases) in both humans and animals are associated with range of negative effects on mental/physical performance, health and well-being. There is already substantial interest in how modern visual displays and artificial lights affect the clock. On the one hand, there is concern that too much light at night and/or too little natural light during the day (as e.g. for indoor reared animals) impact clock phase. On the other, there is excitement in the possibility that by changing the characteristics of light one could design systems that better support natural rhythms. Until now that effort has concentrated on the impact of different light intensities. Its colour has been considered but only insofar as some wavelengths more effectively induce a 'brightness' response in the clock. Our data also argue that we should think about its true colour. The experiments described here represent the essential steps in determining whether and how we can modulate colour to support appropriate circadian physiology in man and domestic animals.