FROM SCHOLASTIC AND THE SCIENTISTS OF THE NATIONAL INSTITUTE ON DRUG ABUSE, NATIONAL INSTITUTES OF HEALTH, U.S. DEPARTMENT OF H EALTH AND HUMAN SERVICES puts out a response. This output provides the basis for our behaviors and actions. While this process is basically the same for teens and adults, the devil is in the details. Since the brain is not fully developed until the early 20s, the way in which a teen’s decision-making circuit integrates information may put him or her at a higher risk of making decisions the teen could later regret. THE TEEN BRAIN: Under Construction Not long ago, scientists thought the human brain was fully mature long before the teen years. While research shows that one’s brain reaches its maximum size between ages 12 and 14 (depending on whether you are a girl or a boy), it also shows that brain development is far from complete. Regions of the brain continue to mature all the way through a person’s early 20s. A key brain region that matures late is the prefrontal cortex , located directly behind your forehead. The prefrontal cortex is very important as a control center for thinking ahead and sizing up risks and rewards. (This area is, in fact, the little red light that was trying to warn you about sending that e-mail.) Meanwhile, another part of the brain that matures earlier is the limbic system , which plays a central role in emotional responses. Since the limbic system matures earlier, it is more likely to gain an upper hand in decision making. This relationship between the emotional center (limbic system) and control center (prefrontal cortex) helps to explain a teen’s inclination to rush decisions. In other words, when teens make choices in emotionally charged situations, those choices are often more weighted in feelings (the mature limbic system) over logic (the not-yet-mature prefrontal cortex). This is also why teens are more likely to make “bad” choices, such as using drugs, alcohol, and tobacco—all of which pose a risk of serious health consequences. “Most kids don’t really ‘plan’to use drugs,” says Professor Laurence Steinberg of Temple University, “at least not the first time. They are more likely to experiment on the spur of the moment , particularly when influenced by others [peer pressure].” FINE-TUNING THE BRAIN Like the rest of the body, the brain needs to mature in order to reach peak performance. This process involves slow changes— strongly influenced by brain activity—that have evolved to fine tune (or optimize) how neural impulses flow throughout the brain, allowing it to process information faster and more reliably. Inside the brain, information travels through a network of neurons, which have thread-like fibers called axons and branch-like structures called dendrites . Dendrites bring information into the neurons, while axons take it away and pass it along to the next neuron. Thus, neurons are assembled into circuits where the far end of an axon (its terminal) is positioned close to a dendrite. The small space between the two is called a synapse —where information is exchanged. Throughout childhood and adolescence, the brain is busy fine-tuning itself through two key processes: myelination and synaptic pruning. Axon Cell body Cell body Myelin sheath Dendrites Dendrites Direction of impulse Axon terminals Synapse A synapse is the small space where an axon and dendrite exchange information.