The paper
D.C. Fernandez et al., “Light affects mood and learning through distinct retina-brain pathways,” Cell, 175:71–84.e18, 2018.
Depressive feelings associated with fewer hours of daylight in winter were once considered an indirect consequence of circadian rhythm disruption. But in 2012, chronobiologist Samer Hattar, then of Johns Hopkins University, and colleagues showed that light can boost mood scores—along with learning ability—in mice, even when sleep and circadian rhythms are unperturbed.
To understand these effects, the researchers looked at recently discovered photoreceptors known as intrinsically photosensitive retinal ganglion cells (ipRGCs), which unlike rods and cones play no role in image formation. “Anatomical data suggested that [the] cells can directly influence several brain areas involved in mood and learning functions,” study coauthor Diego Fernandez of the National Institute of Mental Health, where Hattar now works, writes in an email.
Unexpectedly, transgenic mice with different populations of ipRGCs ablated revealed two independent pathways ...
