Blue lights up the brain

29 November 2007

Light isn't just for seeing, it influences our body clock, mood and short-term memory too. But how? Now new research reveals that just one colour of light - blue - gets our brains on the go more than any other. So is blue the colour that's controlling our behaviour?

Antenna investigates...

Image: Stock.XCHNG/Heather Foley

When light streams into our eyes, it hits the retina at the back. The retina is one of the most well studied tissues in the whole human body, but it's so complicated that there's still lots scientists don't know about it.
What scientists do know is that when light hits the retina, cells there send signals to our brain. These signals reveal the world around us, but also help set our body clock, keep us alert, and help us think and remember. Light therapy can even affect our emotions.

Less light during winter can make people depressed by changing the balance of chemicals in the brain - a light therapy box like this can ease symptoms.

Image: Adam Barney

Scientists understand pretty well how our brains process visual signals. But now a team in Belgium and the UK have begun to unravel how we process light signals for other things too.
'We asked people to complete a test which used their short-term memory - it required them to think and concentrate while a scanner watched what their brains were doing,' says scientist Gilles Vandewalle. 'The test was repeated in different colours of light to see whether it made any difference to brain activity.'

Gilles Vandewalle, brain expert, University of Montreal.

The scientists used a functional magnetic resonance imaging (fMRI) scanner to study the brain. Here, the red shows intense activity in the brainstem.

Image: Vandewalle et al. 2007/PLoS ONE

The scientists found that after just a few seconds of light, areas of the brain known to control alertness became more active. And it was blue light that increased this the most.
So what might this mean?
These results suggest that our eyes have light-sensing cells dedicated solely to collecting non-visual information. And the likely candidate is a type of cell only discovered a few years ago: a cell that scientists know contains a pigment called melanopsin, which reacts to blue light.

Cells in the eye called rods and cones control our vision. Are there other cells that control things like alertness and that could increase short-term memory?

Image: Peter Munro, UCL

Ignacio Provencio, one of the scientists who originally discovered these blue light-detecting cells, thinks this might be the case.
'The responses to blue light shown in this experiment suggest that these melanopsin-containing cells in the retina control some of the body's responses to light.'

Ignacio Provencio, brain expert, University of Virginia.

Scientists have studied macaques to see how their brains and eyes interact.

Image: Erik K Veland

Scientists already know that in animals such as mice and macaque monkeys, these cells connect the eye with the brain to control both visual and non-visual responses. This is another clue to suggest that melanopsin-containing cells control behaviours such as alertness using blue light.
It's not surprising that blue light has such a strong effect on our brain. Natural daylight contains lots of blue light, so it makes sense that we would have evolved to make the most of it.
Gilles thinks his team's findings could be applied to our everyday lives. 'Our research shows that the colour composition of light is important. We might be able to adapt the colour composition of light to suit different activities, such as having blue light to help us concentrate at school or work.'

Could a greater amount of blue in artificial lights help us stay alert?

Image: Dino Abatzidis

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