How our internal clock tells us when it’s time for lunch



Our circadian rhythm, the internal “clock” that tells our bodies when to be active and when to sleep, sets itself largely based on changes in light. However, in addition to these light-related cues, the parts of the brain that regulate circadian rhythms also receive a continual influx of information from other parts of the brain and nervous system that is unrelated to light exposure. How the brain integrates these two types of information to set daily rhythms is largely unknown.


A group of scientists led by Samer Hattar, Ph.D., studied circadian rhythms in mice born without the retinal cells that relay information from the eyes to the brain. They found that these mice do not properly develop connections between the two brain areas needed to establish circadian rhythms, called the intergeniculate leaflet (IGL) and the suprachiasmatic nucleus (SCN). Surprisingly, the animals also forget when it is time to eat, a type of daily rhythm that depends on cues unrelated to light.


The study is the first to reveal a brain circuit linking the retina, IGL, and SCN that uses information unrelated to light to guide eating behavior in mice. If human circadian rhythms employ the same neural pathways as those identified in this animal study, the discovery of a circadian circuit that influences feelings of hunger could potentially provide a promising new approach for the development of treatments for eating disorders.


Fernandez DC, Ruchi K, Langel J, Ma J, Duy PQ, Penzo MA, Zhao H, Hattar S. (2020). Retinal innervation tunes circuits that drive nonphotic entrainment to food. Nature. May; 581(7807);194-198. doi: 10.1038/s41586-020-2204-1.

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This page was last updated on Thursday, June 8, 2023