But it is in a period of great change and opportunities.
“The long development period gives the brain more time to become specialized.” Giedd, chief of the Unit on Brain Imaging in the Child Psychiatry Branch at the National Institute for Mental Health, thinks this can be “empowering for teens” as they try new things and build the skills that could shape the rest of their lives. “Plasticity has vulnerabilities, but has many, many upsides.”
Just what is happening inside an adolescent’s brain?
Neurons, brain cells that send electrical impulses to relay messages, have long axons. As we move into our mid-20s, axons in the prefrontal cortex—the brain’s decision-making and critical thinking hub—become fully myelinated, or covered with an insulating sheath that makes neuron-to-neuron communication 100 times faster.
Illustration © Kathryn Born
During adolescence, connectivity increases greatly. This impacts decision making and other higher order processes. “The prefrontal cortex needs input from every other part of the brain. It’s where everything comes together,” said Giedd. This may contribute to why it is one of the last areas of the brain to mature, and why teen decision making processes may include more risk taking, sensation seeking, and peer affiliation than similar processes in adults. The teen brain’s development processes may also have something to do with the onset of many mental illnesses, like depression, schizophrenia, and eating disorders.
As our brains become myelinated, gaining white matter, they lose plasticity, with less neural growth and fewer connections made.
The brain overproduces connections and gray matter into adolescence, then goes through a selective elimination. “There’s something non-random about what remains,” said Giedd, adding that any number of environmental influences—parenting, diet, sports activities, music practice—can impact cortical thickness.
In addition to these gray and white matter changes, the brain’s reward circuitry changes during puberty, making teens more attracted to novelty and influenced by peers. But, said Giedd, “teens know what’s dangerous when given hypothetical situations.” In real life, however, “complicated dynamics” can get in the way of good choices.