Orange light wakes our circadian eye

FEELING dopey? Wake up your “circadian eye” with orange light. Light is a powerful wake-up  call, enhancing alertness and activity. Its effect is controlled by  a group of cells in the eyeball that make the light-sensing pigment melanopsin. These cells, which work separately to the rods and cones needed for vision, are thought to reset our body clocks – or circadian rhythms. To find out how melanopsin wakes up the brain, Gilles Vandewalle at the University of Liege, Belgium, and his team gave 16 people a 10-minute blast of  blue or orange light while they performed a memory test in an fMRI scanner. They were then blindfolded for 70 minutes, before being retested under a green light. People initially exposed to orange light had greater brain activity in several regions related to alertness and cognition when they were retested, compared to those pre-exposed to blue light. Orange light, which has the longer wavelength, is known to make melanopsin more light-sensitive.  Blue light has the opposite effect, with green lying in the middle. Vandewalle thinks melanopsin is acting as a kind of switch, sending different signals to the brain depending on its state (PNAS, DOI: 10.1073/pnas.1320005111).