LOS ANGELES -- The impulse to smoke cigarettes may be one of the conscious urges that are intimately involved with the insula, a cortical region of the brain, according to researchers here. A damaged insula, they discovered, makes smokers forget to smoke.
LOS ANGELES, Jan. 25 -- Smokers can try the patch. They can quit cold turkey. They can chew nicotine gum.
But when it comes to stopping smoking easily and with finality, according to researchers here, damage to a small area of the brain beats them all.
Smokers who had damage to the insula -- a cortical region linked to conscious urges -- tended to stop smoking abruptly, essentially forgetting the impulse to smoke, found Antoine Bechara, Ph.D., of the University of Southern California.
The effect was seen much more rarely in smokers with damage to other parts of their brains, Dr. Bechara and colleagues reported in the Jan. 26 issue of Science.
The researchers identified 19 smokers with damage to the insula, six in the right insula and 13 in the left. Also they found 50 smokers who had damage to other brain regions.
Most of the lesions were caused by strokes, said Dr. Bechara, although some were the result of surgical resection of meningiomas and epileptic foci. The average age at time of lesion was 47, or 48.4 for patients with insula damage and 45.4 for those with other damage.
The average age was was 55 for the two groups, 57 for those with insula damage, 53 for the others.
All of the patients had been smoking more than five cigarettes a day for more than two years when they suffered the damage, Dr. Bechara and colleagues said.
Of the 19 patients with insula damage, 13 quit smoking, while of the 50 with other damage, 19 quit, but the difference was not statistically significant, Dr. Bechara and colleagues reported.
Presumably some patients stopped the habit in fear of the negative consequences while others stopped because the brain damage disrupted their habit, the researchers said.
To clarify the issue, patients were classified as having a disruption of their addiction if they met four criteria:
According to these criteria, 16 patients who quit smoking were classified as having a disruption of their addiction, while 16 quitters who failed to meet all four -as well as 37 who did not quit -- were considered to have no addiction disruption.
Statistical analysis showed that those with insula damage were about 22 times as likely to have their addiction disrupted than those with other forms of damage. The odds ratio was 22.05, which was statistically significant at P=0.0005.
Indeed, of the 13 quitters with insula damage, 12 reported they did so quickly and easily, with no subsequent urge to smoke. The researchers quoted one of them as saying "my body forgot the urge to smoke."
In contrast, only four of 19 of the patients who quit smoking after a noninsula lesion did so with a disruption of smoking addiction. Thus the odds ratio for quitting smoking with disruption of smoking addiction after a lesion in the insula relative to noninsula lesioned patients was 136.49 with a P value of 0.00008.
It's unclear why the other six patients with insula damage did not quit smoking and it's also not known why four of those with other forms of damage also met the four criteria for addiction disruption.
"One of the most difficult problems in any form of addiction is the difficulty in stopping the urge to smoke, to take a drug, or to eat for that matter," Dr. Bechara said in a statement. "Now we have identified a brain target for further research into dealing with that urge."
The idea that the insula, a regional enclosed by the cerebral cortex, might be a platform for feelings and emotion was first proposed by Antonio Damasio, M.D., Ph.D., also of USC. Dr. Damasio was not involved in this study.
"It's really intriguing to think that disrupting this region breaks the pleasure feelings associated with smoking," he said in a statement. "It is immediate. It's not that they smoke less. They don't smoke, period."
This research was supported by grants from the National Institute on Drug Abuse and the National Institute of Neurological Disorders and Stroke. The researchers did not report any financial conflicts.