The first reason I think teen brains are different from adult brains, is because of the growth occurring in the brain. Just before puberty, there is a growth spurt in the frontal cortex. There are two waves of this growth spurt. Other things that grow, is the grey matter that surrounds the brain; it thickens. Coupled with the growing is also losing. The teen brain grows connections, and also loses the ones that are not used. All this mentioned above causes a great imbalance in the brain, making it very unstable unlike the adult brain. This is the first reason.
The second reason the teen brains thought processes are different from adult brains, is because the teen brain uses different parts of the brain to characterize things than do adult brains. In the film, Inside the Teenage Brain, there was a study that made children and adults identify what moods were represented in a set of pictures. During this time an MRI was scanning the brain, to tell which part of the brain was being used. Surprisingly, the teen brain uses different parts of the brain than the adults do, too see emotion. The teens also identified different emotions, which were described by adults. Seeing this you can really see that teen brains are different than adult brains.
All in all looking at the new studies, and experiments being done by scientists, the teenage brain might finally be unscrambled. But