Impulsiveness and perseveration are opposite behaviors with the same underlying cause.

Immaturity of the prefrontal cortex

Explanation:

The prefrontal cortex is an immature part of teenagers. It develops in teenagers till the age of 20. It is different from the adult prefrontal cortex. The teenagers have not to control the shots of the brain.

It creates difficulties in the other brain structure to use in the right direction. There is a difference in the prefrontal cortex of teenagers and adults as when teenagers make the decision their decision power located at the back of the brain but adults' decision power located in the frontal cortex.

Thus due to the underdevelopment of prefrontal cortex impulsiveness and perseveration are the opposite behavior with the same cause that underlies.