A small area of the brain nestled inside the cerebral cortex might explain why smoking is such a hard habit to break.
A new study of 69 smokers with brain injuries showed that those who had damage to the insula often quit smoking suddenly and effortlessly, suggesting that this particular area could be a target for future therapies to help smokers quit.
"This is the first study to show in humans that there's a brain area that's somehow necessary to promote addiction to any drug, and smoking in particular," said study author Dr. Nasir Naqvi, a doctoral student in the medical scientists' training program at the University of Iowa Carver College of Medicine. The report is published in the Jan. 26 issue of Science.
"This is a seminal paper," said Deborah Mash, a professor of neurology at the University of Miami Miller School of Medicine. "However, the fundamental question is whether the effect is specific to nicotine, because it may be that the insula is the seat of the soul for the compulsive taking of all abused substances."
Trigger for study
The study was prompted by the experience of one patient, a two-pack-a-day smoker who quit immediately after his insula was damaged by a stroke. His body "forgot the urge to smoke," he told researchers.
The insula's function seems to be to take information from other parts of the body and translate that into feelings such as fear, disgust, anger and sadness, along with desires and cravings.
Although some imaging studies have shown that this region of the brain is activated by drug-related cues, "the insula has never really been examined closely for its role in addiction," Naqvi said.
Naqvi and his colleagues found 69 additional patients with brain damage, all of whom had been smokers before the damage occurred. Nineteen of the participants had brain damage involving the insula, 13 of these had quit smoking, and 12 of them had done so quickly and easily.
While some of the other patients also quit smoking, those with damage to the insula were more likely to have quit immediately and without anguish.
Reducing the 'reward'
The results led the study authors to conclude that damage to this region of the brain reduced the urge to smoke, rather than reducing the "reward" associated with smoking. That's not to say that the reward system isn't important to smoking addiction, just that this latest finding might complete the picture, they added.
"A lot of pleasure that comes out of smoking is what it does to the body, rather than nicotine reaching the brain. Each puff stimulates sensations in the throat, the lungs, the chest, and these are important for why smoking is pleasurable," Naqvi explained. "We think that when people are craving cigarettes, they are remembering that type of pleasure, and this area of the brain, which is known to sense what is going on in the body, may play a role in remembering that type of pleasure."
So far, the thought is just a theory, but the finding may help smokers quit using, for example, sensory replacements for smoking such as cigarettes without nicotine.
And, depending on what other research turns up, focusing on the insula may help people give up other addictive behaviours as well, the researchers added.
"This is a seminal paper," said Deborah Mash, professor of neurology at the University of Miami Miller School of Medicine. "However, the fundamental question is whether the effect is specific to nicotine, because it may be that the insula is the seat of the soul for the compulsive taking of all abused substances." - HealthDay News, January 2007
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