[Edythe] London and her colleagues focused on a brain region called the insula, since previous studies in animal and adults showed that its size and volume were affected by smoking. Of the regions in the cortical, or memory, awareness and language parts of the brain, the insula contains the most receptors for nicotine. The region is responsible for decision-making and helping to establish a person's conscious awareness of his internal state. In studies of stroke patients, smokers who lost function of the right insula in the stroke quit smoking, and reported feeling no cravings for nicotine. And in earlier studies London's team conducted, they found a strong relationship between how much smokers who watched videos of people smoking experienced cravings for cigarettes and the activity of the insula, which lit up on PET scans.
When London's team looked at the brains of the 18 smoking teens and 24 non-smoking adolescents, aged 16 to 21 years, using structural MRI, they found no differences overall in the insula region. But a closer examination revealed that the right insula of the smokers was thinner than those of the nonsmokers.
"The brain is still undergoing development when someone is in their late teens," she says. "It's possible that smoking during this period could have effects that could alter tobacco dependence later in life, and that the insult could alter the trajectory of brain development."
While the study doesn't establish whether the differences in the insula can lead to smoking, or is the result of smoking, London says it highlights the role that the brain region may play in how people respond to nicotine and cigarettes. "I think this is very exciting because it points to a vulnerability, a potential vulnerability factor either to become nicotine dependent or for the effects of smoking to ultimately alter the trajectory of brain development," she says. That trajectory could affect not only smoking behavior but decision-making in general, since the insula is important in such assessments.