Published online 11 July 2006 | Nature | doi:10.1038/news060710-2

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Wiping out one part of the brain can break the thrall of smoking.

Kicking the habbit is easy for some with selective brain damage. © Getty

Strokes often change a person's character, depending on where the damage hits. Some may become more impulsive, others depressed. Now researchers have shown that damage to a small but very specific brain area can wipe out an addiction to smoking.

Antoine Bechera, of the University of Iowa in Iowa City, has identified 14 patients who all stopped smoking immediately after having a stroke that damaged their insular cortex. This seems to be not because they were concerned about their health, but because they had lost all interest in cigarettes, he told the Federation of Neuroscience Societies in Vienna this week. "One or two had even forgotten that they used to smoke," says Bechera.

The insular cortex is a relatively primitive part of the brain whose functions include providing an emotional context for experiences, such as drug taking, along with some higher-level, decision-making functions involved, for example, in forming memories.

The seemingly huge impact of switching off this area could have implications for addiction research in general, according to Bechera. Throwing off an addiction for good is tough because cues in the environment — a whiff of tobacco smoke, or the room where you used to shoot up — automatically invokes the emotion associated with the last fix.

But such triggers don't seem to trouble the patients with a damaged insula. "We could do everything we wanted to reawaken craving in these patients," says Bechera. "We could even light up in front of them but it had no effect at all."

Inconstant craving

Bechera's experience with these patients supports his hypothesis that addiction is caused by an imbalance between two neuronal systems — the impulsive system controlled by a brain area (the amygdala) that helps to process emotions and a reflective system controlled by the forebrain. The reflective system anticipates and assesses the consequences, good or bad, that any action will have for the future. Most addiction research focuses on the impulsive system.

Bechera has previously shown that some drug addicts behave similarly to stroke patients with forebrain damage when it comes to decision making. In tests designed to assess financial risk-taking behaviour, they impulsively chose to take as much cash as possible up front, even when that option is linked to a major loss of cash in the longer term. This implies that their impulsive system is winning out over the more logical, risk-assessing system.

But other addicts will make the clever decision — to take less cash up front and benefit long-term. These kinds of addicts tend to have more functional lives, says Bechera. "They have not broken up their families, and they hold down their jobs, because their reflective system is not damaged and they make sensible decisions."

"I think these kinds of addicts will find it easier to stay off drugs if they go clean," he adds.

Kick the habit

Selective damage to the insula cortex seems to filter out some of the information from the impulsive system when it comes to making a decision. As a result, smokers whose reflective capacities are functional seem to be able to make the rational decision to give up, without experiencing withdrawal pain, Bechera says.

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Just how this information could be used to help addicts in general is not yet clear. "But first of all it is important to pinpoint exactly where the systems can become damaged," says Bechera. It may be possible in the future to suppress neuronal activity in the insula, for example, to see if that helps addicts to kick their habits.

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