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A recent study shows that the relationship between the human brain and the sun is less than we originally believed. In fact, it may be that a few thousand years ago, sunlight was more important for human survival than we once realized.
From the Smithsonian:
The sunlight hypothesis has dominated the brain science community for decades, with many thinking that exposure to the ultraviolet (UV) radiation of the summer sun was essential for survival. In this study, Dr. David Reich, from the Stanford University School of Medicine, and colleagues found that this is no longer the case.
The sun’s light is more harmful if it has just about been overhead or just minutes in front of a window.
Reich’s team used brain MRI to map brain activity in the monkeys, monkeys that live near palm trees and whose brains would be more susceptible to sunburn in the hot, humid climate of the Amazon jungle.
The researchers focused on the area of the brain that controls body-heat regulation —the “cholinergic” portion of the brain, or “ventilatory system,” where an action potential can trigger skin-to-skin contact with the body. It turns out that the brain has evolved to respond to the sun’s UV radiation as an urgent health condition. It uses this information to regulate the body-heat level and maintains homeostasis.
This system was first discovered during a pioneering experiment where the Japanese army found that troops without adequate clothing could die of hot water thirst within minutes of exposure to midday sun. This was, as they say, a black swan event.
The monkey brain is still relatively immature: it is about one-third to two-thirds the size of the human. But it has the potential to perceive visual information, and the authors conclude that in a developing brain, light might be a more important determinant of life span than we previously believed.
The monkey model is not necessarily helpful for humans, since it has limitations in that it does not work in the extreme heat or humidity of a human living in the jungle. Still, Reich suspects this discovery may be of great use in research in developing