In 2013, the CRC researchers and their colleagues at Harvard and the University of Montreal argued strongly in favour of the involvement of melanopsin-expressing ganglion cells in brain response recorded during a cognitive and auditory task(2). For this task, the researchers recruited 3 of those very rare blind people who still have their melanopsin-expressing ganglion cells (9 at the time of the study). Thanks to FMRI technology, they were able to demonstrate that the brain responses of these subjects were strongly affected by the presence or absence of blue light during the test. “Nevertheless, these results do not allow us to draw any definitive conclusions with regard to the involvement of melanopsin in the brain responses of sighted people”, indicates Gilles Vandewalle. “Indeed, being blind for several years clearly changes brain function”.

Melanopsin and light

The neuroscientists at CRC wanted to go a step further and, in order to do so, formed a collaboration with Howard Cooper’s team, at the Chronobiology Department of the Stem Cell and Brain Research Institute at INSERM (Lyon). This researcher had notably demonstrated that in both animals and humans, melanopsin is a photopigment capable of regenerating itself. In this way, it is different to cones and rods. When cones and rods capture a photon and transmit the light to the brain, they become inactive and have to transit by means of a specialized cell whose mission is to regenerate them. While melanopsin becomes inactive, it too, having captured and transmitted light information, is capable of regenerating itself spontaneously in the cell that harbors it, on contact with a photon with a different wavelength to that to which it is most sensitive: blue at 480 nanometers.

“Melanopsin is less sensitive to green (520 nanometers), and even less so to red (600 nanometers)”, explains Gilles Vandewalle. “On the other hand, it is the red that shows maximum efficiency in terms of its self-regeneration. The green that we chose as a light-test for our experiments (see infr) has the property of converting the same proportion of molecules of active melanopsin into inactive molecules as it has for converting inactive molecules of the pigment into active molecules”.

Howard Cooper had earlier observed that in rat and human brains, for the pupil to contract, initial exposure to red light increases sensitivity to a blue or green light-test that is then projected. In other words, in the experiments carried out by the INSERM researcher, the intensity of the responses modulated by melanopsin-expressing ganglion cells depended on the light environment which was in place before the test.

Could it be possible to demonstrate the same phenomenon in the human brain? This is the mystery that Gilles Vandewalle and his Belgian and French collaborators tried to unravel. Sixteen healthy young participants helped with an auditory task. Letters were called out to them. They had to continuously determine if each of the letters corresponded to the one that was presented three steps beforehand. “It was a working memory test named the 3-back test”, explains Gilles Vandewalle.

(2) Vandewalle G, Collignon O, Hull JT, Daneault V, Albouy G, Lepore F, Doyon J, Czeisler C, Dumont M, Lockley S, Carrier J (2013), Blue Light Stimulates Cognitive Brain Activity in Visually Blind Individuals,  Journal of Cognitive Neuroscience 25(12):2072-85