The purpose of sleep appears to change when we are toddlers

By Jessica Hamzelou

Cavan Images/Getty Images

Why do we sleep? The answer may depend on the person’s age, according to research that suggests the main role of sleep changes at the age of around two-and-a-half.

Newborn babies spend a lot of time sleeping, and this gradually reduces as they get older. To find out why sleep changes as the brain develops, Van Savage at the University of California, Los Angeles, and his colleagues collected published data on brain activity and size and sleep duration across different age groups.

They used this information to build a …