Because of the development still ongoing in a teenager's brain, it actually functions differently than an adult's brain, according to Frontline. For example, one study that asked respondents to identify the person's emotion in a photograph found that the teens used their amygdala, while the adults used the frontal cortex.
The amygdala is a small part of the brain that provides guidance for instinctive reactions. The frontal cortex manages planning and reason. In the study that showed a fearful face, the adults identified the emotion correctly, but the teens thought that the woman was shocked or angry. The fact that their response came from an area managing instinctive responses, while the adult responses involved reasoning, provides explanation for some of the differences in decision-making in the two groups. The frontal cortex in the teenagers is still undergoing some development and is not ready for that stimulus.
Research finds that the brain does not take on its fully adult form until a person reaches his early 20s, according to the National Institute of Mental Health. This explains why, even though teenagers are so close to their peak of strength, physical ability and mental capacity, it is so dangerous for many. Death by injury is about six times as likely between the ages of 15 and 19 than between the ages of 10 and 14. Alcohol abuse and crime happen at their greatest rate during this age as well.