The colour blue accentuates the responses of those regions of the brain involved in emotion processing and cognition. Researchers at the University of Liege and INSERM have succeeded in demonstrating the direct involvement of a particular type of cell in the retina, melanopsin-expressing ganglion cells, in the impact that light has on the brain activity underlying cognition. This work argues in favour of light systems where the colour blue would be enhanced. It appears that this would be a way of improving cognitive performance and dealing with mood disorders. The work was published in the Journal PNAS.

It has been known for a long time that there are two types of retinal photoreceptors involved in vision: cones and rods. They are connected to nerve cells called ganglions cells which receive information from them and transmit this information to the brain. Slightly more than ten years ago, the work of Ignacio Provencio, at the Department of Biology of the University of Virginia, revealed the existence of a type of ganglion cell that is intrinsically photosensitive: melanopsin-expressing ganglion cells. Melanopsin were an unknown light pigment up to that point. Particularly sensitive to blue light in wavelengths that are in the region of 480 nanometers, these ganglion cells of a “new kind” account for around only 3% to 5% of retinal ganglia. They are dedicated to the regulation of non-visual light effects. Therefore they serve as a base for direct transmission of light information to the suprachiasmatic nucleus, our ‘biological clock’.

A member of Pierre Maquet’s team, at the Cyclotron Research Center (CRC) of the University of Liege(ULg), Gilles Vandewalle, who is also a research associate at the FNRS, has a very special interest in the non-visual impact of light on brain activity and, more particularly, on the regulation of waking, sleeping, cognition or emotions. He is trying to shed light on the underlying mechanisms by focussing mainly on Functional magnetic resonance imaging (FMRI).

The emotions prefer blue

In October 2010, the journal Proceedings of the National Academy of Science of the USA (PNAS) published the results of a study(1) devoted to the immediate effect of light and its colour on the way the brain processes emotions (see also; Blue against seasonal blues). Carried out by researchers at the CRC of the University of Liege, the Surrey Sleep Research Centre (University of Surrey), as well as the Genova Center for Neuroscience and the Swiss Center for Affective Sciences (University of Geneva), this work showed that the colour of ambient light influences the way in which the brain deals with emotional stimuli. The colour blue, the one to which the melanopsin-expressing ganglion cells are most sensitive increases the response to these stimuli.

You don’t need to be a genius to state that most people feel in better humour in summer, happier in themselves, more joyful, to the extent that we intuitively establish a link between light and humour. Some of us suffer from a recurrent depressive syndrome which takes place around October and disappears when the good weather arrives: seasonal affective disorder (SAD). It’s “lighter version”, the winter blues, which is manifested by tiredness, loss of morale, sleep disorders, irritability, etc., affects around 15% of individuals in our part of the world. Everything points to the fact that light affects a person’s mood. And light therapy confirms this idea because it has been shown that exposure of the retina to high-intensity white light is beneficial for fighting SAD and the winter blues. More recently, various works have underlined the superiority of blue light for this type of treatment.

(1) Vandewalle G, Schwartz S, Grandjean D, Wuillaume C, Balteau E, Degueldre  C, Schabus M, Phillips C, Luxen A, Dijk DJ, Maquet P (2010), Spectral quality of light modulates emotional brain responses in humans, Proceedings of the National Academy of Science of the USA 107(45):19549-54