Monday, January 29, 2007

The insula and addiction to smoking.

I've mentioned in a previous post the growing evidence that the insula is the 'sensory cortex' of the body interior, representing visceral body states.

Naqvi et al have found that smokers with brain damage involving the insula are more likely than smokers with brain damage not involving the insula to undergo a disruption of smoking addiction, characterized by the ability to quit smoking easily, immediately, without relapse, and without persistence of the urge to smoke.

Here is a figure from their paper:

From the figure legend: "Whole-brain region-by-region logistic regression analysis. The only regions that were assigned a color were those for which the number of patients was sufficient to detect a statistically significant effect. Regions for which there was a statistically significant association between a lesion and a disruption of smoking addiction (P < 0.05, uncorrected) are highlighted in red. The insula is the only region on either side of the brain where a lesion was significantly associated with a disruption of smoking addiction. The likelihood of having a disruption of smoking addiction was not increased after damage in the orbitofrontal cortex."

From their discussion:

"The results of this study suggest that the insula is a critical neural substrate for the urge to smoke, although they do not in themselves indicate why the insula, a region known to play a role in the representation of the bodily states), would play such an important role in urge. A clue may be provided by the account of one patient in our sample who quit smoking immediately after he suffered a stroke that damaged his left insula. He stated that he quit because his "body forgot the urge to smoke" . His experience suggests that the insula plays a role in the feeling that smoking is a bodily need. Indeed, much of the pleasure and satiety that is obtained from smoking is derived from its bodily effects, in particular its impact on the airway. In addition, nicotine withdrawal is associated with changes in autonomic and endocrine function, which may contribute to its unpleasantness. Current evidence suggests that the insula plays a role in conscious feelings by anticipating the bodily effects of emotional events. The insula may therefore function in the conscious urge to smoke by anticipating pleasure from the airway effects of smoking and/or relief from the aversive autonomic effects of nicotine withdrawal. Thus, damage to the insula could lead a smoker to feel that his or her body has "forgotten" the urge to smoke."

1 comment:

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