This is the VOA Special English Health Report.

Chemical dependency can result from many things: alcohol, caffeine, illegal drugs like cocaine, legal drugs like pain killers. But one of the most difficult dependencies to break is also one of the most common: smoking. The body becomes addicted to the nicotine in tobacco. Now, researchers may have found an important link in the brain to smoking addiction.

Scientists at the University of Southern California and the University of Iowa studied thirty-two former smokers. All of the men and women had brain injuries as a result of strokes.

Half of them reported that they were able to give up cigarettes quickly and easily after they suffered the brain damage. Magnetic resonance imaging showed that twelve of those sixteen patients had suffered damage to a part of the brain called the insula.

The insula is found near the ear. Experts believe it somehow brings together emotional experience and sensory information with some activities like breathing. Experiments have suggested that the insula has a lot to do with the experience of pain and some basic emotions like fear, anger and happiness.

The patients in the study had all smoked at least five cigarettes a day for two years. One of the sixteen who reported that they quit smoking immediately and without effort had smoked as many as forty a day. 

Antoine Bechara was one of the leaders of the study. He and co-author Hanna Damasio work at the Brain and Creativity Institute, a new center at the University of Southern California in Los Angeles. The other authors of the study were Nasir Naqvi and David Rudrauf of the University of Iowa.

Antoine Bechara says the insula is not the only area of the brain involved in cigarette addiction. He says many parts of the brain are connected with substance dependency. But he says damage to the insula does seem to destroy a necessary link in the smoking addiction.

The patients did not lose all dependencies -- they still had a normal desire for food, for example. This may suggest that the insula is more responsible for dependencies that come from a learned pleasure, like smoking. And the researchers say their discovery may point to a weak spot in smoking addiction.

They say it could lead to better ways to help people stop smoking -- but much more research is needed. The findings appeared in Science magazine.

And that's the VOA Special English Health Report, written by Caty Weaver. You can find transcripts of our reports and audio files at voaspecialenglish.com. I'm Barbara Klein.