Your Brain: The Missing Manual

The Teenage Years

It's a time of turbulence, when hormones rage, tempers flare, and the brain's logical thinking systems go offline—and that's just the parents. Whether you're living through them or parenting someone who is, the teenage years have a well deserved reputation as a trying time.

In the past, scientists believed the teenage brain was essentially the same as the adult brain, minus a few life lessons. The infamous teenage moodiness was chalked up to the effect of the sex hormones you learned about in Chapter 9. However, several new studies have uncovered dramatic evidence that the teenage brain is still a work in progress.

Here are some of the events that happen to the teenage brain:

• A second wave of synapses grow. Between 7 and 11 years, the brain repeats the same trick it used in the first two years of its life. It produces a huge growth of dendrites that stretch out in search of other neurons. This second wave happens just before puberty, but it's not linked to it—for example, if puberty is delayed for other reasons (such as poor nutrition), this brain boost still takes place. As a child becomes a teenager, the synaptic pruning begins again.

• Myelination continues. The myelination process that began in childhood is still underway. The areas that are myelinated last include the prefrontal cortex (The Thinking Brain), which forms the seat of higher reasoning and impulse control. It isn't fully online until the age of 18 to 20.

• Patterns of brain activity are different