On Light and Mood

The discovery of atypical mammalian photoreceptors that are distinct from the classical rod and cone photoreceptors opened new avenues for light research. The non-rod/non-cone photoreceptors belong to retinal ganglion cells (RGCs) and express the photopigment melanopsin rendering them intrinsically photosensitive RGCs or ipRGCs for short. We showed that these cells project widely in the brain and are in position to control many essential behaviors, which include circadian rhythms and sleep. Recently, we found that ipRGCs also have a direct influence on mood and learning & memory. In this presentation, I am going to present unpublished data where my lab uncovered a new brain region that is essential for the direct light effects on mood. I will present anatomical and functional evidence that this region is both necessary and sufficient for mood regulation by light. These studies open new avenues to understand major depressive mechanisms, especially the ones related to seasonal changes.