A new study confirmed the vital role of sleep in building and maintaining the brain, through a sudden shift in sleep function that occurs at the age of about 2.4 years, when its primary goal changes from building the brain to maintenance and repair.

Researchers said they conducted a statistical analysis of data from more than 60 sleep studies. They studied sleep duration, duration of REM sleep, brain size and body size, and created a mathematical model for how sleep changes during growth.

There are basically two types of sleep, each of which is associated with specific waves and nerve activity in the brain. The rapid eye movement phase, in which the eye moves rapidly from side to side behind closed eyelids, is a deep sleep with vivid dreams. The non-REM sleep phase is largely dreamless.

During the REM sleep phase, the brain forms new nerve connections by building and strengthening what are known as nerve connections, which enable nerve cells to communicate, which leads to enhancing the ability to learn and consolidate memories.

During sleep, the brain also repairs a modest amount of daily neurological damage to the genes and proteins within neurons, in addition to removing the by-products that accumulate.

The results showed that, at the age of about 2.4 years, the basic function of sleep changes from building and cutting connections during the deep sleep phase to neuronal repair during the REM and non-REM sleep phase.

“We were astonished that this shift is happening as if there is a button … it is severely interrupted,” said Van Savage, professor of ecology, evolutionary biology and computational medicine at the University of California, Los Angeles, and a senior author of the research published in the journal Science Advances.

The period of rapid eye movement sleep decreases with age. Newborn babies, who can sleep about 16 hours a day, spend about 50 percent of their sleep time in the stage of rapid eye movement sleep, but a clear reduction occurs at the age of about 2.4 years.

This percentage drops to about 25 percent by the age of ten and to between about 10 and 15 percent by the age of 50.

Reuters quoted Van Savage, “Sleep is a requirement of the animal kingdom almost everywhere, like eating and breathing … I see it as one of the pillars of human health.”