Smokers with injuries in a specific part of their brains kick their habits instantly -- without the intense cravings that can make it so hard to quit, a new study reports today.
The researchers from USC and the University of Iowa linked a brain area called the insula to the powerful urges that cause people to continue smoking.
Smokers with damaged insulas were 136 times more likely to have their addictions erased than smokers with damage in other parts of their brains, researchers said.
One man who smoked an average of 40 cigarettes a day before a stroke damaged his insula was surprised to suddenly lose all cravings for tobacco. He told researchers his body "forgot the urge to smoke."
"It was like a switch was turned off," said Antoine Bechara, a neuroscientist at USC and senior author of the paper.
The research in the journal Science opens a new front in addiction research and could lead to improved treatments for smokers, experts say.
Though intentionally damaging the insula would be too risky, it might be possible to develop drugs or medical devices that could temporarily disable the region's circuitry, relieving smokers of the urge long enough for them to quit, scientists said.
But Jed Rose, director of the Center for Nicotine and Smoking Cessation Research at Duke University, cautioned against drawing broad conclusions from the research. Rose, who was not involved in the research, said people with conditions such as attention-deficit disorder have high rates of smoking, suggesting different regions of the brain might also be important in such people.
Of the 45 million Americans who smoke, 400,000 die annually of illnesses related to smoking. Rose said no more than 5% of smokers are able to permanently quit on their own.
Most smoking research has focused on the cortex, the brain region involved in reasoning and decision making. Nicotine in tobacco prompts the release of brain chemicals in the cortex that generate pleasurable feelings. Smoking addiction has been largely understood as a drive to feel pleasure, said Caltech neurobiologist Henry Lester.
Smoking-cessation drugs target the brain's pleasure circuitry but are not very effective in helping smokers quit over the long term, Rose said.
The researchers examined 32 former smokers who had suffered some form of brain damage. The patients were asked how hard it was for them to stop smoking and whether they felt any urges to smoke after they quit.
Sixteen of the patients said they quit effortlessly after their brain injury.
The scientists used brain imaging equipment to identify the damaged area of patients' brains. Of the 16 patients who found it easy to quit smoking, 12 had damaged insulas. The remaining patients showed injuries in other parts of their brains.
Bechara said that in patients with damaged insulas, other brain circuits involved in addiction remained intact. The result shows "if we can knock out this one area, we can disrupt the whole cycle of addiction," he said.
The insula, about the size of an apricot, is believed to integrate emotions with information about certain bodily functions, such as pulse rate or breathing. The information is processed instantaneously. For example, a smoker might become calm when a puff of smoke enters the lungs.
Lester said the insula helped explain why so many smokers likened their addiction to bodily needs, such as thirst.
In the study, damage to the insula did not affect urges necessary to survival, such as appetite. Bechara said the insula's function probably was confined to learned preferences and behaviors, meaning it might have a role in gambling addictions or obesity.
Dr. Gene-Jack Wang, an addiction researcher at Brookhaven National Laboratory, said previous studies suggested a role for the insula in cocaine addiction. When addicts were shown drug paraphernalia, brain imaging equipment detected activity in their insulas, he said. Wang said he published that study in 1999 but did not understand the significance of his finding at the time.
The latest study "is very important and will generate a lot of interest in the insula and our future understanding of cravings for food, drugs and addictive behaviors," Wang said.