BioMed
UK scientist Sarah-Jayne Blakemore explains how teenage brains develop into the twenties, connecting changes in grey matter with peer pressure, risk, and learning.
Scientists long assumed the brain was essentially finished by childhood. Imaging of living brains shows it keeps reorganizing through the teenage years and into the twenties. Grey matter shrinks while white matter grows, and the region behind planning and self-control matures slowly.
Brain systems that respond to reward tend to mature earlier than the front-of-brain systems for self-control and judging risk. During the gap, rewards feel especially tempting while the ability to hold back is still developing. This mismatch is one likely explanation for why teenagers take more risks.
Teenage behaviors often dismissed as faulty or abnormal make sense given the brain changes happening at that age. Adolescence is a distinct stage with its own features, not a defect on the way to adulthood. Mocking teenagers as brainless misreads what is actually going on.
Adolescence is when most people settle on a stable sense of who they are and how they want others to see them. That work shows up as more comparing oneself with others, caring about others' opinions, embarrassment, and wrongly assuming everyone is watching. How the brain processes thinking about oneself also shifts in these years.
Being left out causes more anxiety and low mood in adolescents than in adults. Isolation during these years can leave lasting marks on brain structure, hormone levels, and later behavior. Peer approval is a strong need at this age, not a passing whim.
About three-quarters of mental illnesses, including depression, addiction, and schizophrenia, first appear by the end of adolescence. Heavy use of alcohol or cannabis in these years can harm the brain more than the same use in adulthood and can lower later thinking ability. The same period of change that offers opportunity also brings vulnerability.
The evidence does not show screens themselves to be good or bad for young people. The clearer harm is lost sleep, which screen use may contribute to. That is one reason the book argues secondary schools should start later.
Teenagers respond more to how an action will play out socially right now than to warnings about long-term harm. To reduce risky behavior, point to immediate social consequences, either instead of or alongside sober warnings about the distant future. The pull of peers explains risk-taking, and the same pull works on adults too.
Adolescence is a time of great creativity and opportunity, and it is essential to becoming a healthy adult. Many young people build businesses, write software, make music, compete, and do science. The aim should be to support and celebrate this period rather than treat it as a problem to be managed.
Brain studies produce findings, not facts, and certainty about brain development is not possible. Turning neuroscience into rules for teaching or parenting is rarely straightforward. Claims about the brain should be met with real skepticism.