Glia are ascendant during adolescence. The brain begins pruning unused neurons. The volume of white matter (glia) grows 5% between age 10 and adulthood, while gray matter (nerve cells) peaks at age 11–12, then falls.
The adolescent brain is primed for learning. Doing so keeps cells alive; otherwise they are lost from disuse.
The prefrontal cortex is the last to mature. It is instrumental in the control of impulses, reasoning, planning, and rational decision-making.
With the brain undergoing significant changes, puberty is an especial time of irritable and irrational behaviors. A sense of reward satisfaction lingers in teenagers, limiting impulse control and leading to inappropriate behaviors by acting in a social context that has already past.
The fact that the reward is gone doesn’t matter. An adolescent will act as if the reward is still there. ~ American psychologist Shaun Vecera
Teenagers are prone to take risks without cognizance of potential consequences. This comes from a still developing mind-brain lacking matured capacity for sound judgment.