Melatonin actually causes a shift much larger than ten to twenty minutes -when taken early. Melatonin taken in the morning causes a large shift to delay the cycle (this can cause a shift of several hours). Melatonin taken after several hours hastens the cycle, also by hours. If this weren’t the case, it would be useless as I currently use it. The ten to twenty minutes is as a sedative, when taken twenty minutes before bedtime.
There are, of course, a number of pathways affecting sleep timing, including the uninformatively named System X that just tries to keep track of time by dead reckoning. I believe, perhaps wrongly, that the SCN’s sleep related functions are mostly directly by melatonin; melatonin reduces the firing rates of the parts of the SCN that increase in firing rate in the presence of light (according to Wikipedia). This is the core timing mechanism of how light affects the SCN, isn’t it?
Edit: Looking at it again, the relevant part of the SCN article ( https://en.wikipedia.org/wiki/Suprachiasmatic_nucleus )(in the electrophysiology section) does not have direct citations, but I’ll assume it’s correct unless this activity of melatonin is directly disputed.
Edited again: An edit changed the structure of what I was saying, making for a strange sentence I don’t endorse.
Melatonin actually causes a shift much larger than ten to twenty minutes -when taken early. Melatonin taken in the morning causes a large shift to delay the cycle (this can cause a shift of several hours). Melatonin taken after several hours hastens the cycle, also by hours. If this weren’t the case, it would be useless as I currently use it. The ten to twenty minutes is as a sedative, when taken twenty minutes before bedtime.
There are, of course, a number of pathways affecting sleep timing, including the uninformatively named System X that just tries to keep track of time by dead reckoning. I believe, perhaps wrongly, that the SCN’s sleep related functions are mostly directly by melatonin; melatonin reduces the firing rates of the parts of the SCN that increase in firing rate in the presence of light (according to Wikipedia). This is the core timing mechanism of how light affects the SCN, isn’t it?
Edit: Looking at it again, the relevant part of the SCN article ( https://en.wikipedia.org/wiki/Suprachiasmatic_nucleus )(in the electrophysiology section) does not have direct citations, but I’ll assume it’s correct unless this activity of melatonin is directly disputed.
Edited again: An edit changed the structure of what I was saying, making for a strange sentence I don’t endorse.