Why We Sleep?

Sleep performs a number of important functions for life, but scientists often have wondered why we spend so much of our lives sleeping. 

A new study has found that the main reason for sleep changes between infancy and right before the age of 3.

For years, scientists have debated two theories about the main function of sleep. One theory suggests the brain uses sleep to organize connections between its cells and develop networks that support memory and learning. The other theory says sleep’s most important job is to clear the metabolic waste that builds up throughout the day. 

This study, published Sept. 18 in the journal Science Advances, found that infants spent most of their time in deep REM sleep, which lends itself to building new connections between brain cells. When the children in the study reached the age of 2 ½ the amount of time spent in REM sleep decreased and the brain moved into maintenance mode, according to a Sept. 22 Live Science article.

“It was definitely shocking to us that this transition was so sharp,” said senior author Van Savage, a professor of ecology, evolutionary biology and computational medicine at the University of California, Los Angeles and the Santa Fe Institute in New Mexico.

The researchers used existing data from more than 60 studies to compile several hundred data points on newborns and children up to the age of 15. They then built a mathematical model to track data points through time and see what patterns emerged, the article said. In the future, they plan to use their mathematical model to track sleep in animals to see if a similar shift occurs.

“Humans are known to be unusual in the amount of brain development that occurs after birth,” said lead author Junyu Cao, an assistant professor in the Department of Information, Risk and Operations Management at The University of Texas at Austin. 

“Therefore, it is conceivable that the phase transition described here for humans may occur earlier in other species, possibly even before birth.”