The Brain Continues to Grow into Young Adulthood
Studies using magnetic resonance imaging (MRI) techniques, involving brain scans at regular intervals, show that the brain continues to grow and develop into young adulthood (at least to the mid-twenties). Right before puberty, adolescent brains experience a growth spurt that occurs mainly in the frontal lobe, which is the area that governs planning, impulse control, and reasoning. During the teenage years, the brain again goes through a process of pruning synapses—somewhat like the infant and toddler brain (National Institute of Mental Health, 2001).
As the teenager grows into young adulthood, the brain develops more myelin to insulate the nerve fibers and speed neural processing, and this myelination occurs last in the frontal lobe. MRI comparisons between the brains of teenagers and the brains of young adults have shown that most of the brain areas were the same—that is, the teenage brain had reached maturity in the areas that govern such abilities as speech and sensory capabilities. The major difference was the immaturity of the teenage brain in the frontal lobe and in the myelination of that area (National Institute of Mental Health, 2001).
Another change that happens during adolescence is the growth and transformation of the limbic system, which is responsible for our emotions. Teenagers may rely on their more primitive limbic system in interpreting emotions and reacting, since they lack the more mature cortex that can override the limbic response (Chamberlain, 2009).