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Comment by klogw | Hacker News Reader

Can someone explain what is the feedback mechanism to self-correct the clock? This biological clock like any other clock will deviate from the true time after a while, maybe weeks or months; so what is the self-correcting mechanism in the biological clock?

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https://en.wikipedia.org/wiki/Suprachiasmatic_nucleus

The SCN receives input from specialized photosensitive ganglion cells in the retina via the retinohypothalamic tract. Neurons in the ventrolateral SCN (vlSCN) have the ability for light-induced gene expression. Melanopsin-containing ganglion cells in the retina have a direct connection to the ventrolateral SCN via the retinohypothalamic tract. When the retina receives light, the vlSCN relays this information throughout the SCN allowing entrainment, synchronization, of the person's or animal's daily rhythms to the 24-hour cycle in nature.

And importantly, the photosensitive ganglion cells are most sensitive to blue wavelengths of light, which is why a lot of people recommend avoiding blue light at night.

Off-hand I do not have a good reference (maybe this? https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4078443/ ) but I've heard quite often that both light and food have an impact on our body clocks, and that the systems operate more or less independently. Perhaps someone out there who knows more can clarify.

It's been several years since I took my neurobiology class in undergrad. There has been a lot of research in this area. You're right that the clock does deviate (I checked Wikipedia and it looks like in the absence of light humans' circadian rhythm cycles on just over 24hr). Exposure to light helps tweak the cycle.

It is entrained to rhythmic external cues, synchronised oscillators.

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