A study published in today’s issue of Science shows that people with damage to a part of the brain called the insular cortex often lose the urge to smoke cigarettes.
Antoine Bechara, a neuroscientist and physician at the University of Southern California, led the study, in which nearly 70 smokers took part. 19 of the participants had incurred damage to the insula as a result of a stroke, or in some other way. Of these, 12 stopped smoking immediately after incurring the injury to their brain. In contrast, only 4 of 50 patients with damage to other regions of their brains stopped smoking afterwards.
The insular cortex, or insula (the red rectangle in the coronal section on the left), is a small brain region found on the medial (inner) surface of the temporal lobe; it is known to play a role in decision-making and in putting sensory experiences into an emotional context. It is, therefore, thought that the insula is involved in producing the craving for nicotine and other addictive substances. For example, neuroimaging studies show that the insula is activated when cocaine addicts are shown images of drug paraphernalia.
Bechara hypothesizes that addiction is caused by an imbalance between two neural circuits – one which includes the amygdala and is involved in controlling impulsive behaviour, and another in the forebrain which anticipates and assesses the consequences of one’s actions. In a previous study of financial risk-taking behaviour, Bechara showed that drug addicts sometimes behaved like stroke patients with forebrain damage; when offered the choice between taking a a small or a large sum of money up front, they impulsively chose the latter option, even if it was associated with a large financial loss in the future.
The findings published today provide further insights into the biological basis of addictive behaviour. They could help in developing effective ways to help people kick their addictive habits. People who are trying to give up smoking, for example, can get a sudden urge for a cigarette if they see someone else smoking. Because the insula appears to be involved in generating these cues, Bechara suggests that nicotine-free cigarettes would satisfy the cravings by providing physical cues which activate the insula, and may therefore be more effective than nicotine gum or patches in helping smokers overcome their addiction.
References/ Further reading:
Naqvi, N. H. et al. (2007). Damage to the insula disrupts addiction to cigarette smoking. Science 315: 531-534.
Esch, T. & Stefano, G. B. (2005). The neurobiology of pleasure, reward processes, addiction and their health implications. Neuroendocrinol. Lett. 25: 235-251.