"It is assumed that the brain adapts to the repeated nicotine-induced release of dopamine by producing less dopamine," said lead study author Dr. Lena Rademacher of Lubeck University in Germany.
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Then, they offered cessation treatment to the smokers and did another set of brain scans three months later on the subset of 15 people in this group who had quit.
But in the second set of scans, there was no longer a difference between nonsmokers and the smokers who successfully quit during the study.
Nicotine addiction is known to be associated with abnormalities in the dopamine system. But scientists are uncertain if smoking induces those abnormalities or if they already exist in some people and make them more vulnerable to getting hooked on nicotine.
"In case of a predisposing trait, abnormalities are expected to persist with abstinence," Rademacher said. "Conversely, if dopamine function normalizes with abstinence this rather indicates that alterations were induced by substance consumption."
Overly preoccupied with drug use
Even so, the results are encouraging because they suggest that brain function is plastic, or modifiable, and that an ex-smoker's brain can return to more normal functioning over time, said Joseph McClernon, a psychiatry researcher at Duke University School of Medicine in Durham, North Carolina, who wasn't involved in the study.
"To the extent that smoking or other drug use alters how this system functions normally can have impacts on behaviour that increase the likelihood that one continues to use drugs or has difficulty in quitting drug use," McClernon said.