It was only in 1991 that Dr. Jay Giedd started the first long-term, longitudinal study of the changes going on in the adolescent brain by using sequential functional MRI scans of some eighteen hundred teenagers over a number of years1.
This research led Giedd and others to challenge the earlier assumption by Swiss psychologist Jean Piaget (and Dr. Spock), that brain development was pretty much complete by the age of twelve. What scientists are now coming to understand is that while the brain is some 90 – 95% of its adult size by adolescence, the teenage years are a period of incredible structural change within the brain. In fact, Giedd has found that “the changes taking place in the brain during adolescence are so profound, they may rival the early years as a critical period of development2. These changes affect some of our highest functions, and continue into our twenties.
There are several key issues here. One is that the gray matter in the frontal and temporal lobes is the last to mature (that remaining 5-10%). And the frontal lobe, or more precisely the prefrontal cortex, is the home of the so-called “executive functions” – things like planning, organization, judgment, impulse control and reasoning – that is, the parts that would normally tell a human body not to dive off the 40- foot bridge into unknown water. And so we can see a potential explanation for the teenage propensity for risk-taking, impulsive behaviour and an inability to get that project completed on time.
And it’s not just that certain areas are still growing. It seems that some things aren’t quite ‘hooked up’ the same way as they will be as an adult. Dr. Deborah Yurgelun-Todd, director of neuropsychology and cognitive neuroimaging at McLean Hospital in Massachusetts, has done some very interesting work in how teens read the facial emotions of others. While adults are able to easily identify images of facial emotions like fear, many teens get it wrong. Moreover, these MRI scans show that in adolescents (unlike adults), there was almost no activity in the prefrontal cortex while doing the task. Teens instead showed activity almost exclusively in the limbic area of the brain — the area especially connected to emotions3. Teens essentially had an emotional response largely unmediated by judgment and reasoning. Such researach provides more clues to the seemingly inexplicable responses of adolescents. But they may also provide guidance as to how we might better engage a teenager – through their emotions.
Adolescent brain activity is not just about areas of the brain that are still under development. It’s also about what’s happening in the existing gray matter – restructuring. There is an ongoing process of arborization (where neurons grow new and bushier connections) and a simultaneous pruning of neural pathways that aren’t getting much use. The neurons that survive go on to myelination, where they are insulated to enhance their performance. The end result is that the pathways that get used not only survive, but they get stronger. It is the ultimate ‘use it or lose it’ scenario. It is what scientist Gerald Edelman calls “neural Darwinism” — the survival of the fittest synapses. Different activities — playing sports, memorizing historical facts, solving problems, drinking, watching T.V, etc. — all influence how the adolescent’s brain will ultimately be wired. Those who start smoking during adolescence, for example, will likely have a much harder time quitting later in life than those who take up smoking in their twenties; the addiction, according to researchers at Duke University in Durham, North Carolina, appears to get hard-wired during the teen years4.
Knowing that teenage brains require rich experiences to forge new connections and strengthen positive neural pathways, we need to carefully consider the content and experience of secondary education. Are schools helping to ‘prune out’ creativity? Are they building the capabilities needed to communicate, collaborate, investigate and solve problems? Are we inadvertently building the wrong skills?
It’s clear that adolescence is a time of massive restructuring in the brain. But what is the purpose? Researchers are are now coming to understand that this process of synaptic upheaval is a critical evolutionary adaptation that makes it possible and essential for youth to become independent and ready to start a life – and build a future – of their own.
Emphasis on standards and results: (1) undermines students’ interest in learning, (2) makes failure seem overwhelming, (3) leads students to avoid challenging themselves, (4) reduces the quality of learning, and (5) invites students to think about how smart they are instead of how hard they tried.
Programs at Work
- Jay Giedd interview, Inside the Teenage Brain – with Dr. jay Giedd, Frontline PBS.
- Giedd, as above.
- Dr. Deborah Yurgelun-Todd interview, Inside the Teenage Brain with Dr. Yurgelun-Todd, Frontline, PBS.
- News Release from Duke University Medical Centre, Early Nicotine Use May Lead to Lasting Addiction, 2003.