Why do small things sleep longer?

Why do mice sleep five times longer than elephants? Why do babies sleep longer than adults? If these sound like riddles, it’s because they were. Despite its ubiquity, sleep has a mystery that has puzzled scientists for decades.

Currently, a team of scientists, including researchers at the Santa Fe Institute, are the first to use data from humans and other mammals to explain why interspecific and developing sleep time decreases as the brain grows. We have developed one of the quantitative models. Importantly, the model identifies abrupt changes at about 2.4 years of age. As the main purpose of sleep shifts from reorganization to repair, human sleep patterns change.

“Looking at sleep and seeing how it changes gives us insight into something really fundamental about brain development,” said Shannan High Attorney and former Chairman of SFI. Says Geoffrey West, a theoretical physicist.

A previous study by physicist and biologist West and Van Savage, a professor at UCLA and an outside professor at SFI, examined differences in sleep time between mammals. New research Scientific progress It links phylogeny-evolutionary relationships between species-and ontogeny-organizational development with aging-into an integrated framework.

Experts suggest many possible reasons for sleep, but the two most prominent are the reorganization and repair of the nerves that are essentially learning. During wakefulness, the brain experiences wear due to blood flow and daily production of harmful chemicals. Sleep gets rid of this. The brain reorganizes and repairs primarily when sleeping–the West likens it to a subway repair that takes place at night to avoid normal traffic disruptions.

Sleep time can be roughly classified into REM (random eye movement) and NREM (non-REM). Colloquially, REM sleep is well known as “deep sleep,” but its purpose remains unresolved.

To answer questions about REM and NREM, the new model reduces to a series of simple equations that capture how the brain uses energy to process information (which needs to be reorganized). The author then enters data from various studies examining sleep time, metabolic rate, and brain size in dozens of participants, from infants to adolescents.

By determining the ratio of REM to NREM to total sleep time-among other factors such as brain size-the researchers were able to use the model to predict their purpose. While NREM handles routine repairs that occur throughout life, it turns out that REM sleep is primarily the cause of reorganization / learning that dominates early development.

At about 2.4 years of age, the researchers observed a sudden change in most of the sleep transition from REM to NREM. In other words, humans sleep less, in part, because they don’t have to form so many new neural connections. According to Savage, this transition point has not been identified so far, but it can have a significant impact on development.

“In the meantime, the brain is doing something really amazing and very different,” he says. “What are the consequences of the ability to learn a language and adapt the brain to different situations?”

Preliminary measurements of other animals under development (rabbits, rats, guinea pigs) show similarities to human sleep, but to determine if all mammalian babies follow the same rapid changes. Is premature.

“I’m very interested in extending our framework to other mammals,” said Junyu Cao, a researcher and lead author of the paper at the University of Texas at Austin.

The study began at SFI in 2007, when Savage was a postdoctoral fellow working with West. It has since evolved through a series of workshops and working groups as part of the institute’s ongoing research on the laws of biological scaling and complex time.

reference:

Cao J, Herman AB, West GB, Poe G, Savage VM. Elucidate why we are asleep: Quantitative analysis reveals a sudden transition from nerve reorganization to early developmental repair. Scientific progress.. 2020; 6 (38): eaba0398. two:10.1126 / sciadv.aba0398

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