Depressed? Watching TV at Night Might Not Be Helping

To understand why daytime light can improve depression, while nighttime light can cause it, researchers in China conducted a sophisticated series of experiments in mice to examine the impact of 2 hours of blue light either in the middle of the day (BLID) or at night (BLAN).

Three weeks of BLAN, but not BLID, induced persistent depression-like behaviors in mice (anhedonia and helpless behavior), without alterations in circadian rhythms, overall behavior, or sleep. This effect was mediated by connections among retinal ganglion cells that mediate non–image-forming vision, the dorsal perihabenular nucleus, and the nucleus accumbens. A nighttime circadian rhythm gated this circuit, making it sensitive to activation by BLAN but not by BLID.