Why Has My Teenager Turned into an Alien?

Your child may have suddenly become a moody mutant, but science lifts the lid on the dramatic brain transformations during this most misunderstood part of our lives.

Many parent-child misunderstandings arise because a teen’s body and brain don’t grow in harmony. Adolescence—the total period of mental transition from childhood to adulthood—takes longer than puberty, its physical equivalent. In fact, the brain is in adolescence from the age of 9 to the mid-20s. The law may say that they’re adults at 18, but their heads are only half-cooked! The adolescent brain is a work in progress. It’s not an overgrown child brain, nor is it an underdeveloped adult brain—MRI scans have revealed it is unique in its flexibility and capacity to learn.

Changing in shape, structure, and internal chemistry, your teenager’s maturing brain is an easily excitable, socially sensitive machine that drinks in life experiences. In early childhood, gray matter on the brain’s rippled surface (where the computing happens) inflated in size, sprouting millions of interconnected microscopic branches. However, by the ages of 12–14, that gray matter needs trimming back for efficient adult thought to bloom. Gray matter shrinks at first as unused brain pathways are cut, in much the same way that pruning a rose bush allows larger, stronger branches to develop. During this time of profound brain changes, your teenager can be prone to misjudgments and impulsive behavior.

Sex hormones often get the blame for a teen’s erratic moods—but they’re only part of the story. The brains of adolescents develop in a back-to-front order: the inner, emotional circuitry becomes adultlike long before the self-controlled, thinking regions in the brain’s frontal lobes do. With the swirl of emotion-conveying tissue deep within the brain firing on all cylinders, teens’ emotions have an adult intensity but without the measured restraint of a fully formed frontal lobe. A teen will suddenly know what they want (“I want to stay over at Billy’s house!”) but they’re not yet able to reason it out in an adult way (“Why? You saw him yesterday.” “Because I do!”).

The still-changing frontal lobes also explain why adolescents are rarely paragons of subtlety. Teens are still learning to see the world from another person’s perspective, and they lack the expertise to read other people’s expressions. As a result, teens may be tactless, blurt out something inappropriate, or miss the nuances of speech. The rhetorical reprimand of a teacher, “Are you sure you want to do that?”, may be met with an obnoxious-sounding, “Yes, I am!” Research shows that it is much more effective for teachers and parents to be unambiguous: “Please stop doing that.”