Growing up together in the same household, siblings are often privy to inside information about one another. A new brain imaging study now shows that one sibling’s brain may hold valuable clues about another sibling’s behavior. Your brother or sister’s lips may be sealed, but their brain has much to tell.

It has long been known that the brains of people addicted to drugs do not look the same as the healthy non-addicted person’s brain. What has not been known is whether those brain abnormalities existed prior to drug use or developed as a result.

Researchers in Britain devised a clever strategy for finding the answer to that question. The study team used MRI brain imaging to scan 50 sets of siblings in which one sibling was addicted to a substance and the other was not. Interestingly, the researchers found that brains of both the addicted and the non-addicted sibling shared the same abnormalities in the fronto-striatal systems – brain regions which are responsible for the exercise of self-control.

Not every person who takes drugs or drinks alcohol becomes addicted. Plenty of research tells us that a person’s risk of drug addiction is linked to their inability to exercise self-control. Thus, the question becomes why one sibling is able to overcome the brain abnormality and avoid addiction while the other is not.

The researchers say that when they can answer this question they will be well on their way toward developing new therapies and treatments which could prevent at-risk people from ever developing a substance addiction.

In the meantime the study helps to explain why family history of drug use is a risk factor and at the same time demonstrates that a heritable vulnerability toward addiction is a deficit which is able to be overcome.