If we as human beings were living "naturally", without any artificial light sources, how would we sleep?
What would our natural rhythm look like? What would our sleeping patterns be in the ideal sense? Well it turns out that when people are living without any sort of artificial light at all, they sleep twice every night. They go to bed around 8 PM until midnight and then again they sleep from 2 AM until sunrise. And in between they have a sort of meditative quiet in bed. During this time there is a surge of prolactin the likes of which a modern day never sees. The people in these studies report feeling so awake during the daytime that they realize they are experiencing true wakefulness for the first times in their lives.
This article describes additional benefits:
In fact, during clinical experiments at the National Institute of Mental Health, human subjects deprived of light at night for weeks at a time exhibited a segmented pattern of sleep closely resembling that related in historical sources (as well as that still exhibited by many wild mammals). The subjects also experienced, during intervals of wakefulness, measurably higher levels of prolactin, the hormone that allows hens to sit happily upon their eggs for long periods.
These elevations of prolactin reinforce historical descriptions of complacent feelings at "first waking" and, back then, probably helped calm people's worries about the night's perils. Prolactin is also what differentiates segmented sleep, with its interval of "non-anxious wakefulness" that nearly resembles a meditative state, from the tossing-and-turning insomnia we medicate against.
First, her assertion that people naturally sleep in two segments at night (known as segmented sleep) is well supported by a landmark paper by Thomas Wehr published in the Journal of Sleep Research. Back in 1992, while at the National Institute of Mental Health, Wehr demonstrated that people put into winter-like periods of sunlight (<10 hours) would develop a biphasic sleep. Essentially they slept, woke up, and slept again. During that intermediate waking period, the body produced larger amounts of the hormone prolactin (Gamble mentions this). Prolactin is reponsible for lactation in mammals, but it has also been linked to happiness, sexual gratification, and relaxation. What's so important about prolactin? Well it's one of the necessary hormones for our functioning, it counters dopamine, and it might help you stay smart. Research in the journal Science and the Journal of Neuroscience show that it helps increase mental plasticity in women during pregnancy. It may be doing the same in everyone.
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