“Teens are in a discovery mode,” says Frances Jensen, MD, an HMS professor of neurology. “They’re experiencing new things, and their brains are developing accordingly. There’s simply a lot going on in their brains.”

The teenage brain matures from back to front. The posterior regions, especially those above the spinal column, are largely responsible for motor control. Their earlier maturation helps account for the quick acquisition of locomotion and other movement skills by young people. Maturation of many sensory regions also occurs early, enabling a growing person to learn from the surrounding world. The maturing of the forward regions of the brain, particularly the frontal lobe, doesn’t occur until late adolescence or early adulthood; some researchers say the region’s maturation may not be complete until age 30.

The ease of learning that most teens enjoy, however, can carry a steep cost: addiction. “The brain builds itself as it responds to experiences,” Jensen says. “With teens who experiment with drugs, this can result in addiction. It’s the same pattern as learning—we want more, more, more.”