The human brain uses light not just to support vision but also to support alertness and cognitive tasks.
Which colours of light are most effective and where in the brain these non-visual effects can be seen was previously not known. Now researchers at the Cyclotron Research Centre at the University of Liege and the Surrey Sleep Research Centre at the University of Surrey have ‘shed some novel light’ on these issues by using functional magnetic resonance (fMRI) brain imaging while the participant were engaged on a working memory task.
In a research paper published this week in PLoS ONE it is reported that it is not just any light that is most effective but rather light of a particular short wavelength (480 nm, i.e. blue light rather than violet or green). This is in accordance with the hypothesis that such non-visual effects are mediated by a recently discovered ancient photoreceptor which is particularly sensitive to blue light. More importantly maybe, by using very short exposures to light (< 1 minutes), in combination with brain imaging techniques, the researchers could identify the brain areas that are involved in the initial responses to this light. The brain areas that responded to blue light exposures included areas in the brain stem and the thalamus. These areas are involved in the regulation of very basic aspects of brain function, such as the regulation of alertness and sleepiness.
Other areas that responded to light included the hippocampus and amygdala. These areas are well known to be involved in the regulation of higher functions such as memory and emotion. In summary, these data establish a brain basis for the wide ranging effects of light on how we perform and feel. The data have implications for the development of better artificial light environments and a better understanding of the effects of light on the human brain in general.
Dr Gilles Vandewalle, lead author, comments that ‘ it was impressive to see how only a minor difference in wavelength could have such a dramatically different effect on our fMRI results’. Dr Pierre Maquet co-senior author, comments that ’ as a neurologist I am impressed by the wide ranging effects of light on brain function and the range of brain areas that are affected. This is an area that certainly warrants further investigation.’ Dr Derk-Jan Dijk, co-senior author remarks, ‘ Humans are day-active animals, and maybe it is after all not so surprising to a biologist that blue light has these profound effects on our brain. After all, natural daylight contains quite a bit of blue light. We had simply forgotten about it because we are so preoccupied by the ‘visual’ effects of light, which are not particularly dependent on blue light. We now know that other aspects of brain function are.