For years scientists believed that brain growth was basically complete by the time we hit kindergarten. Modern research however has revealed that brain development continues well into a youth’s 20s (and males peak later than females). “We now understand that the brain of a human being is the last organ in the body to completely develop ” saysFrancesJensen MD FACP professor and chair of the department of neurology at the Perelman School of Medicine University of Pennsylvania and author of The Teenage Brain. By the time a child hits adolescence she explains the amygdala — an almond-shaped section of nervous tissue located in the temporal (side) lobe of the brain responsible for the perception of emotions processing of memories and stimulation — is fully developed. But the prefrontal cortex (the front of the brain) — which is responsible for higher executive functions like planning distinguishing right from wrong determining what’s socially appropriate behavior and decision making — is still under construction. How does a physically immature brain result in immature behavior like poor decision making? By way of example Dr.Jensen explains that a fully developed frontal lobe will be insulated with a fatty white matter called myelin a substance that covers and protects nerves. Just as an electric wire serves as an insulator to help speed the transmission of electrical impulses the myelin serves as an electrical insulator that speeds nerve impulses to other brain cells. The teen brain however is not yet fully coated with myelin so it takes longer for the nerve impulses to travel to their destinations. Practically speaking this means that if a friend says “Hey let’s see if we can clock this car at 100 miles an hour ” a teen whose strong emotion-driven impulse is to say “Yes! Cool!” does not have the ability in that split second to apply cause-and-effect thinking to conclude that this may be an incredibly stupid and dangerous thing to do.