Brain Scans Take a Look Inside the Growing Brain

What brain changes transform children from creatures of impulse into fully functioning adults? In a 2001 study that used fMRI imaging, researchers at the University of Pittsburgh identified the key brain changes that signal mental maturity.

How and where the brain changes

Once a child hits adolescence, the brain, having mastered basic cognitive abilities, no longer grows in size. The adolescent years are a flurry of complex reorganization as the brain decides what’s needed, what’s unnecessary, and how to achieve maximal efficiency.

Adolescent brains undergo synaptic pruning, in which useful neural connections are nourished while lesser connections wither away. Nipping unnecessary synapses in the bud actually leads to deactivation in many regions as the growing brain sheds excess neural activity like baby fat. At the same time, the brain begins to activate regions such as theprefrontal cortex that handle abstract cognitive abilities. Of these abilities,impulse control is key in attaining adult-level mental maturity.

fMRIs reveal where impulse control happens

Researchers used fMRI brain scans to compare brain activation in 254 subjects as they performed an antisaccade task. These subjects were divided into children (ages 8-13), adolescents (14-17), and adults (18-30). Adults performed the best and children the worst, but more interesting is how their differences manifested.

The antisaccade task measures impulse control by tracking subjects’ saccades, or eye movements. As subjects stare at a blank screen, a light flashes briefly. The goal is to look in the opposite direction from the light. This simple premise is a complex task—and, for untrained brains, an effortful one. It requires superior impulse control to both keep task goals in mind and resist the instinct to look.

Children, who made many errors, largely activated the brain's supramarginal gyrus. This may indicate that children relied more on visual cues to compensate for other immature brain processes.

Adolescents, in contrast, activated theprefrontal cortex more than other groups. Activity in this area, which managesworking memory and executive control, evinces brains beginning to maintain higher-level plans and goals.

Adult brains showed the widest pattern of brain activity, lighting up over 5 different brain regions. This is strong evidence that the ability to voluntarily start and stop behavior—to plan rather than merely react—is a mature product of the synaptic pruning and organization that happens in adolescence. The adult brain is an efficient engine, quickly processing varied information to form a cohesive strategy.