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Which part of the brain controls nicotine addiction?

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I’ve written before about how nicotine from tobacco smoke affects the “reward center” of the brain. Nicotine from smoke is carried from the lungs to the brain via the arterial circulation in 10-15 seconds. The nicotine binds to nicotinic receptors in the ventral tegmental area of the brain, causing burst firing in a series of fibres leading to the nucleus accumbens, eventually causing a release and overflow of dopamine, the reward neurotransmitter. That effect is believed to cause the feeling of satisfaction from smoking, and the smoker very quickly learns to associate the feeling with the situations and behaviors leading up to it. Thus being in a situation where smoking often occurs (on the phone, driving the car, in the bar etc) comes to trigger an expectation and desire for that feeling, and opening a pack and lighting up the cigarette can produce a conditioned positive subjective feeling even before any smoke is inhaled (or even if the cigarette has been denicotinized. These processes and brain regions are conventionally believed to be critical to nicotine addiction.

However, I primarily wanted to tell you about a study that took a different approach to identifying the key area of the brain for nicotine addiction. The study by Nasir Naqvi and colleagues was published in Science in January 2007, and examined a group of smokers who had suffered various forms of brain damage (typically via a stroke).
They specifically wanted to examine whether damage to a part of the brain called the “insula” was associated with spontaneous quitting smoking immediately after the brain injury. The insular cortex, or insula, is a relatively small and thin structure deep within the cerebral cortex, between the temporal lobe (controlling memory and emotion) and the frontal lobe (controlling planning and activation of behaviors). Although not fully understood, there is evidence that the insula is responsible for helping us bring to consciousness the link between internal bodily states (like hunger, pain and basic emotions) and external situations and behaviors. One can see that such a function would be important in helping a person remember that when they injected a drug they had a good feeling, and in triggering the desire to inject when the person returned to the place where they first injected (by bringing to consciousness the recollection that injecting felt good in that place).
The researchers reasoned that more smokers who had damage to their insula would spontaneously quit smoking than people who had damage to other parts of their brain. They identified 69 patients who had been smokers prior to their brain injury (smoking an average of 27 cigarettes per day), and split them into those who had damage to the insula (n=19) and those who had damage to other parts of the brain, not including the insula (n=50). Although a high proportion of both groups quit smoking in the years after their brain injury (68% with insula damge versus 38% with non-insula damage), the researchers were particularly interested in those who had a “disruption of smoking addiction”. This meant that they (a) reported quitting smoking less than a day after their brain lesion onset (b) did not start smoking again after they quit, (c) stated that it was relatively easy for them to quit and (d) reported feeling no urges to smoke since they quit.

13 out of 19 smokers with insula damage quit smoking after their brain injury (68%), and of the 13 quitters, 12 quit smoking immediately with disruption of their smoking addiction (described above). Thus of the quitters, 92% of those with insula damage had immediate disruption of smoking addiction, compared with 21% of those with non-insula damage. One of the participants in the study who quit smoking immediately after a stroke that affected his insula commented that, it was as if “my body forgot the urge to smoke.” None of the patients with insula damage who had disruption of smoking addiction reported any reductions in pleasure from eating or desire to eat.

This study suggests that insula damage interferes with some of the specific psychological functions that make it difficult to quit smoking and promote relapse: and particularly the conscious urge to smoke. The findings suggest that conscious awareness of the discomfort caused by smoking abstinence, and that smoking will make you feel better, is a critical part of smoking addiction. The authors of the study suggest that this area of the brain, which has been largely ignored by addiction researchers, should be considered more in understanding addiction, and that drugs affecting insula function may in the future have promise as aids to smoking cessation.

Reference:
Naqvi N, Rudrauf D, Damasio H, Bechara A. Damage to the insula disrupts addiction to smoking. Science 2007: 315 (June 26), 531-534.

The full report of this study can be accessed online at:
http://www.sciencemag.org/cgi/content/full/315/5811/531
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About the Author


MA, MAppSci, PhD

Dr. Jonathan Foulds is an expert in the field of tobacco addiction.

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