How colour corrects your body clock

Your body clock uses colour to determine the time of day, which may even explain how colour vision evolved in the first place...
27 April 2015

Interview with 

Dr Tim Brown, University of Manchester


Your body clock is the mechanism behind your daily rhythms, helping to regulate sleep and wakefulness. It is extremely important: an out-of-sync body clock can cause sleepiness, throw  your appetite even raise your risk of cancer and heart disease. But how does this internal clock set itself? Georgia Mills spoke to researcher Tim Brown...

Tim - Generally, what people have thought up until now was that this works via signals from the eyes that reach the body clock and essentially provide information about the amount of light. So, if there's a lot of light, the clock will know it's daytime. If there's not very much light, it's night time. Of course, the problem with just measuring brightness is that on a cloudy day there'll be less light and so your ability to judge when it's transitioned between day and night will be different than on a clear day. And so, what we found was that actually the clock gets around this by also measuring the colour of light. That changes in a very predictable way around dawn and dusk and importantly, that really isn't affected by cloud cover. So, the colour of light is consistently bluer the lower the sun is below the horizon.

Georgia - How did you go about testing this?

Tim - What we did was create what we describe as an artificial sky. That allowed us to house mice in this environment where we're able to either completely recreate natural dawn and dusk, or provide something that was almost identical except there was no change in colour. So, there was a big change in brightness between day and night, but the colour was fixed to resemble night time. By doing this, we're able to see that under our completely natural recreation of the environment, the body clock of mice was really reliably synchronised to the middle of the night. If we remove that change in colour and just showed them the change in brightness then they were less able to synchronise their activity to night time. In fact, their body clock shifted earlier into the day. So effectively, they perceive night as arriving earlier when we presented colours that resembled night.

Georgia - So, by changing the colour of this artificial sky, you could trick mice essentially into thinking it was a later or an earlier time of day.

Tim - That's right.

Georgia - I know that mice have pretty poor colour vision when you compare them to humans. Can this translate to how people measure the day?

Tim - The main difference between the colour vision in mice and humans is that, of course, humans have this ability to discriminate red and green colours whereas mice, and almost all other mammals, possess this ability to distinguish blue, yellow colours which, of course, humans also have. And this is really the ancestral form of colour vision. In fact, one of the exciting things about our research is that it suggests maybe the original reason why colour vision evolved might have been to tell our body clock what time of day it is. So, in so far as it's present in both mice and humans then we certainly think our findings could translate to humans. But of course definitive proof of that will require a few experiments actually in human subjects.

Georgia - Say, we established that this exact mechanism is what happens in a human brain and that's how our body decides what time of day is, are there any practical applications we can learn from this?

Tim - Well, yeah. I think there's a really exciting potential here. So, what our research has done really is lay the framework which we can use to think about designing new kinds of lighting environments or devices that use changes in colour to adjust how they affect our body clocks. So in general terms, you can think of that working in two ways really. You can design lighting environments for things like workplaces or schools that are designed to maximise the synchronisation of our body clocks to our social or work schedules. And that obviously has the associated benefits that it brings our peek cognitive abilities in line with our work environment. The other way that it could be useful is that of course, there will always be sometimes when say, we need to stay up late and we need light to see what we're doing. But we don't want to reset our body clocks. Under those circumstances, you can think about adjusting the colour of the lighting to minimise the impact it would have on your internal rhythms.


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