Jay Giedd, at the National Institute of Mental Health in Bethesda, Maryland, led the researchers who followed the progress of 400 children, scanning them every two years as they grew up.
They found that adolescence brings waves of so-called 'brain pruning' during which children lose about one per cent of their grey matter every year until their early 20s.
This reduction trims unused neural connections that were overproduced in the childhood growth spurt, starting with the more basic sensory and motor areas of the brain.
These mature first, followed by the regions involved in language and spatial awareness and then finally those involved in more cerebral functions.
Among the last to mature is the very front of the brain's frontal lobe, which is involved in control of impulses, judgement and decision-making, which scientists say might explain some of the bizarre decisions made by the average teenager.
This area also controls and processes emotional information sent from the amygdala - the fight or flight centre of gut reactions - which may account for the short-tempers among some teenagers.
As grey matter is lost, the brain gains white matter, a fatty tissue which helps conduct electrical impulses and stabilise neural connections.
Scientists say that at this stage of life the brain acts as sponge for learning, but the lack of impulse control may lead to risky behaviour such as drug and alcohol abuse, smoking and unprotected sex.
