Teens are notoriously self-conscious. Now brain-imaging experiments are revealing how this adolescent predilection might be the result of changes in brain anatomy linked with the self, and the findings may hint at how the sense of self develops in the brain.

One way we build a sense of self is by reflecting on how others perceive us, a concept psychologists have dubbed “the looking-glass self.” To see how teenagers reacted to what other people thought of them, researchers asked adolescent girls ages 10 to 18 to imagine a variety of scenarios involving onlookers that were designed to evoke social emotions such as guilt or embarrassment—for example, “You were quietly picking your nose, but your friend saw you.”

Cognitive neuroscientist Sarah-Jayne Blakemore of University College London and her colleagues found that when compared with scenarios describing basic emotions that did not involve the opinions of others, such as fear and disgust, girls who thought about onlookers’ opinions engaged a brain region known as the dorsal medial prefrontal cortex (MPFC) more during social emotional scenarios than adult women did. This area is one of the last regions to develop before adulthood, and it is known to activate in adults when they think about themselves, about other people and even about the personality traits of animals.

It makes evolutionary sense for teenagers to be highly concerned about what others think, Blakemore suggests. Adolescence requires becoming more independent because one’s parents might not be around much longer. Teens have to start relying more on what peers think “and develop a more socially constructed sense of self,” Blakemore says. The researchers’ findings “might also help explain why peer influence is so strong in adolescence, compared with before and after.”

Another way we construct a sense of self is by contemplating what our aims or traits are, and previous studies have shown that adolescents also use their dorsal MPFC when engaged in such introspection. For instance, when developmental social neuroscientist Jennifer Pfeifer of the University of Oregon and her colleagues at the Uni-versity of California, Los Angeles, asked subjects whether phrases such as “I make friends easily” described them or a familiar other—in this case, Harry Potter—the researchers found that thinking about oneself caused higher dorsal MPFC activa­tion in teens as compared with adults.

The greater activity in the dorsal MPFC in adolescents hints that they are learning to attribute complex mental states such as intentions both to themselves as well as to other people, suggests social cognitive neuroscientist Kevin Ochsner of Columbia University. As teens mature, less activity may be seen in that region because the brain might become more efficient at the process of self-reflection—somewhat like a skill for which practice makes perfect, he adds.

Pfeifer also explains that in adults more activity is seen in brain regions linked with storing knowledge about oneself. “Instead of deciding who they are over and over again, adults may just retrieve what they already know about themselves,” she says. “But while these areas related to self-reflection might be more active in adolescence, it is something that goes on throughout your whole life—you’ll see the same kinds of processes going on in the brain in adults if they enter stages in their lives that are new to them, such as parenthood.”