Adolescence is a time of striking change in the brain as well as the body. Environment and experiences during this time guide development of some of the human brain’s more complex functions, making the teen years a second critical period of brain development.
The teen brain is like a big ball of clay, ready to be molded by new experiences. Neurons extend their dendritic branches to receive signals from other neurons, and their axons add more insulating myelin to speed signal transmission, especially in the brain’s frontal lobes. At the same time, extensive synaptic pruning culls weaker pathways in a process called competitive elimination. Together, these changes reshape the neural highways that move signals through the brain.
These changes give the teen brain an amazing capacity to learn. Magnetic resonance imaging (MRI) scans of the adolescent brain show that white matter — brain tissue containing heavily myelinated nerve fibers — increases. The increase is especially pronounced in the corpus callosum, the large bundle of myelinated fibers connecting the brain’s right and left hemispheres. Stronger connections between the two sides may explain teens’ enhanced learning capacity.
Enhanced connectivity and an imbalance between the parts of the brain responsible for decision-making and self-control and those involved in motivation and emotion may lead teens to seek new experiences. This makes teens more likely to take risks and seek excitement.
Unfortunately, this can be a double-edged sword: Risk taking and sensation seeking can lead many teens to experiment with drugs and alcohol, increasing the chances of addiction. The brain regions involved in addiction overlap with those supporting learning, memory, and reasoning, prompting some scientists to regard addiction as a type of acquired learning disorder.
Frequent drug use during the teen years damages parts of the brain important for memory, attention, and executive functioning. Teens who drink alcohol possess less gray matter — areas densely packed with neuron cell bodies — and their white matter is also less robust, suggesting their cells may not communicate as well. Studies using functional MRI (fMRI) indicate adolescents who binge-drink have lower brain activity and a harder time sustaining attention compared to their peers who don’t drink. They also perform more poorly on tests measuring working memory, the ability to hold small pieces of information in mind for a short time.
The human brain continues to develop and change even beyond the teen years. Some studies show ongoing changes until about 30 years of age. Different brain regions show different rates of growth and maturation. For example, MRI studies indicate the gray matter density of most brain regions declines with age. But in the left temporal lobe, a region important for memory and language, it increases until age 30. Other changes affect the myelin that protects axons and speeds signaling between cells. Younger brains have more myelin in regions processing visual and auditory information and motivation and emotion. Closer to 30, the frontal and parietal lobes develop more myelin, which aids working memory and higher cognitive functions.
The frontal lobes are the last regions of the brain to fully develop. These regions are important for executive functioning — complex functions like attention, self-control, decision-making, and long-range planning. The late maturation of the frontal lobe might explain some of the characteristics of a “typical teenager,” such as a short attention span, impulsive behavior, and forgetting to do homework. However, none of this means that the teenage brain is broken. It is simply experiencing a critical period of development that also opens the brain to millions of new learning opportunities.
Adapted from the 8th edition of Brain Facts by Melissa Galinato.
About the Author
Melissa Galinato recently earned her PhD in Neurosciences from the University of California, San Diego. She works as a freelance writer and editor, specializing in neuroscience and mental health topics.
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