Gilles Vandewalle and colleagues used an optic fibre to shine bright white light into either the left or right eye of 19 participants, and then left them to sit in the dark. For most of the participants, the light exposure delayed the onset of self-reported sleepiness. Brain imaging showed this sustained alertness was related to altered activity in the thalamus, a structure buried deep in the brain.
Brain imaging also showed the light enhanced the activity of brain regions engaged when the participants subsequently completed an auditory oddball task in the dark (i.e. listen out for odd tones that don’t match all the others). These regions included areas at the front and back of the brain known to be involved in paying attention.
The effects of the light exposure were short-lived, lasting less than 10 minutes beyond the end of the light stimulation. However, the researchers believe their observations are evidence that the brain has a “non-image” forming (NIF) system that responds to light but which is quite separate from vision. They argue the NIF system response outlasts light exposure, in contrast to the classic visual system which only responds during light stimulation. “These findings suggest that light can modulate activity of subcortical structures involved in alertness, thereby dynamically promoting cortical activity in networks involved in ongoing non-visual cognitive processes”, the researchers concluded.
Vandewalle, G., Balteau, E., Philips, C., Degueldre, C., Moreau, V., Sterpenich, V., Albouy, G., Darsaud, A., Desseilles, M., Dang-Vu, T.T., Peigneux, P., Luxen, A., Dijk, D-J. & Maquet, P. (2006). Daytime light exposure dynamically enhances brain responses. Current Biology, 16, 1616-1621.