““Making matters worse, the prefrontal cortex, the part of the brain that governs so much of our higher executive function—the ability to plan and to reason, the ability to control impulses and to self-reflect—is still undergoing crucial structural changes during adolescence and continues to do so until human beings are in their mid- or even late twenties. This is not to say that teenagers lack the tools to reason. Just before puberty, the prefrontal cortex undergoes a huge flurry of activity, enabling kids to better grasp abstractions and understand other points of view. (In Darling’s estimation, these new capabilities are why adolescents seem so fond of arguing—they can actually do it, and not half-badly, for the first time.) But their prefrontal cortexes are still adding myelin, the fatty white substance that speeds up neural transmissions and improves neural connections, which means that adolescents still can’t grasp long-term consequences or think through complicated choices like adults can. Their prefrontal cortexes are also still forming and consolidating connections with the more primitive, emotional parts of the brain—known collectively as the limbic system—which means that adolescents don’t yet have the level of self-control that adults do. And they lack wisdom and experience, which means they often spend a lot of time passionately arguing on behalf of ideas that more seasoned adults find inane. “They’re kind of flying by the seat of their pants,” says Casey. “If they’ve had only one experience that’s pretty intense, but they haven’t had any other experiences in this domain, it’s going to drive their behavior.””
