We can resist sleep for hours, but at some point, perhaps the moment we are awake to protect our lives, we will fall asleep, immobile and vulnerable. Fortunately, after delivery we have the reward: a good night’s sleep will restore the mood for the next day. Then is that it? Do we sleep to rest?
While it has undeniable restorative effects, sleep is not an effective form of rest. If it were so, we would have a considerable gain in energy while sleeping. In practice, only 110 calories are saved for the one who slept at night compared to the other who stayed outdoors. That simple difference is undone when you eat a chicken leg. Surely nature would find another way to reclaim this little energy without neglecting the interaction with the environment, but it turns out that it has preserved sleep over thousands of years of evolution.
Some researchers believe that this single function biological whim arose on Earth and later conquered several ascriptions. Other scientists suggest that sleep is a trait with no adaptive value, just a by-product of some mysterious, genuinely useful action that has yet to be defined.
Russell Foster, a researcher at Oxford University’s circadian neuroscience laboratory, believes he has solved these problems. Sleep was a protection for him. Sleeping animals save themselves the dangers of vigilance. Searching for food and competing for territory or gender are activities in which living things are exposed to real risks, much greater than those caused by rest. Protected and immobile, we are safe.
At first glance, this concept seems very strange, but there are facts that speak for it. For example, the sleeping brain processes information. Studies have shown that the importance of the stimulus is more important than its intensity in waking someone up. This is why meaningful words, your baby’s crying, or hearing your own name are more likely to trigger Awakening than meaningless words, another baby’s crying, or hearing someone else’s name. The brain processes sounds and selects the appropriate information that leads to awakening.
The scientist Masako Tamaki found out even more. She measured the electrical activity of people’s brains while they slept in an unusual place. Tamaki noted that the left hemisphere did not sleep as deeply as the right hemisphere and therefore remained more vigilant to the events surrounding it. The scientist also realized that when the individual sleeps more nights in the new environment, brain activity returns to symmetry during sleep. The conclusion is that the hemispheres of the brain fall asleep asymmetrically in order to maintain a certain level of vigilance guided by the left side of the brain until they adapt to the new shelter. We keep a relative night watch as we get used to the new place.
So sleep forces us to rest, but ensures that we keep a diffuse awareness of the room. While the organism is asleep, the brain uses unconscious processes to choose which stimulus should reach consciousness and, if necessary, wake up immediately. Already awake, we and other mammals, drawn to protrusions, limit our attention to one point and forget about others. For example, an animal that is very careful about food, its inspection of other places, reduces a hazard in natural environments.
However, there is something Foster fails to consider: the strong link between sleep and pleasure. For the Spanish researchers Rial and Canellas, pleasure is the main force that forces us to sleep. Scientists believe that sleep begins when we lose the pleasure of being awake and ends when sleep is no longer comfortable. They also argue that one of the worst ways to torture someone is through sleep deprivation.
Rial and Canellas point out that there is a common regulator of sleep and pleasure: dopamine. This is the neurotransmitter that manages our neurological reward systems, the sources of joy. Drowsiness occurs when the levels of dopamine are lower in the areas of the brain that are responsible for emotions. Sleep ends after dopamine levels are restored, and then we are ready for efficient vigilance.
In search of pleasure or security, the organism falls asleep. Dormindo performs an essential set of biological activities that prepare the body for threats and the pleasure of waking up.
1. Foster RG. Sleeping is not a secret. Psych J. 2018 Dec; 7 (4): 206-203. 208. doi: 10.1002 / pchj.247. PMID: 30561857.
2. Tamaki M, Bang JW, Watanabe T, Sasaki Y. Night watch in one hemisphere of the brain during sleep in connection with the first night effect in humans. Curr Biol. 2016, May 9; 26 (9): 1190-4. doi: 10.1016 / j.cub.2016.02.063. Epub 2016, April 21. PMID: 27112296; PMCID: PMC4864126.
3. Andrillon, T. & Kouider, S. (2020). The watchful sleeper: Neural mechanisms of sensory (de-) coupling during sleep. Current Opinion in Physiology, 15, 47-59.
4. Rial RV, Canellas F., Gamundí A., Akaârir M., Nicolau MC. Pleasure: The missing link in regulating sleep. Neurosci Biobehav Rev. 2018 May; 88: 141-154. doi: 10.1016 / j.neubiorev.2018.03.012. Epub 2018 Mar 13. PMID: 29548930.
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