Scientists have identified an abrupt transition in the role of sleep in the brain at about 2.4 years old when its primary purpose appears to shift from brain building to maintenance and repair.

US researchers conducted an analysis using data from more than 60 sleep studies.

The Californian researchers looked at sleep time, duration of rapid eye movement (REM) sleep, brain size and body size, and devised a mathematical model for how sleep changes during development.

During REM sleep, the brain forms new neural connections by building and strengthening synapses, reinforcing learning and consolidating memories.