Scientists studying stroke patients are reporting that an injury to a specific part of the brain, near the ear, can instantly and permanently break a smoking habit, effectively erasing the most stubborn addiction. People with the injury who stopped smoking found that their bodies, as one man put it, "forgot the urge to smoke."

The finding, which is to appear in the journal Science today, is likely to alter the course of addiction research, experts say, pointing researchers toward new ideas for treatment. Though no one is suggesting brain injury as a solution for addiction, the findings suggest that therapies might focus on the insula, a prune-size region under the frontal lobes that is thought to register gut feelings and seems to be a critical part of the network that sustains addictive behavior.

Previous research on addicts focused on regions of the cortex involved in thinking and decision-making. Although those regions are involved in maintaining habits, the new study suggests that they are not as central.

The study did not examine dependence on alcohol, cocaine or other substances. Yet smoking is as at least as hard to quit as any other habit, and it probably involves the same brain circuits, experts said. Most smokers who manage to quit do so only after repeated attempts, and the craving for cigarettes usually lasts for years, if not for life.

"This is the first time we've shown anything like this, that damage to a specific brain area could remove the problem of addiction entirely," said Dr. Nora Volkow, director of the National Institute on Drug Abuse, which financed the study, along with the National Institute of Neurological Disorders and Stroke. "It's absolutely mind-boggling."

Others cautioned that the study was small, and that scientists still knew little about the widely distributed neural networks involved in sustaining habits.

"One has to be careful not to extrapolate too much based on brain injuries to what's going on in all addictive behavior, in healthy brains," said Dr. Martin Paulus, a psychiatric researcher at the University of California in San Diego, and the San Diego VA Medical Center. Still, he added, the study "opens up a whole new way to think about addiction."