Brain responses to violet, blue, and green monochromatic light exposures in humans: prominent role of blue light and the brainstem.
BACKGROUND
Relatively long duration retinal light exposure elicits nonvisual responses in humans, including modulation of alertness and cognition. These responses are thought to be mediated in part by melanopsin-expressing retinal ganglion cells which are more sensitive to blue light than violet or green light. The contribution of the melanopsin system and the brain mechanisms involved in the establishment of such responses to light remain to be established.


RESULTS
We exposed 15 participants to short duration (50 s) monochromatic violet (430 nm), blue (473 nm), and green (527 nm) light exposures of equal photon flux (10(13)ph/cm(2)/s) while they were performing a working memory task in fMRI. At light onset, blue light, as compared to green light, increased activity in the left hippocampus, left thalamus, and right amygdala. During the task, blue light, as compared to violet light, increased activity in the left middle frontal gyrus, left thalamus and a bilateral area of the brainstem consistent with activation of the locus coeruleus.


CONCLUSIONS
These results support a prominent contribution of melanopsin-expressing retinal ganglion cells to brain responses to light within the very first seconds of an exposure. The results also demonstrate the implication of the brainstem in mediating these responses in humans and speak for a broad involvement of light in the regulation of brain function.
Vandewalle
Gilles
G
Cyclotron Research Centre, University of Liège, Liège, Belgium.
Schmidt
Christina
C
Albouy
Geneviève
G
Sterpenich
Virginie
V
Darsaud
Annabelle
A
Rauchs
Géraldine
G
Berken
Pierre-Yves
PY
Balteau
Evelyne
E
Degueldre
Christian
C
Luxen
André
A
Maquet
Pierre
P
Dijk
Derk-Jan
DJ
D000328:Adult; D000704:Analysis of Variance; D001519:Behavior; D001933:Brain Stem / Q000502:physiology*; D003116:Color; D005260:Female; D006801:Humans; D008027:Light; D008279:Magnetic Resonance Imaging; D008297:Male; D049268:Positron-Emission Tomography