Ex-smokers' brains show rebound in pleasure chemical

"It is assumed that the brain adapts to the repeatednicotine-induced release of dopamine by producing lessdopamine," said lead study author Dr. Lena Rademacher of LubeckUniversity in Germany.

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Then, they offered cessation treatment to the smokers anddid another set of brain scans three months later on the subsetof 15 people in this group who had quit.

But in the second set of scans, there was no longer adifference between nonsmokers and the smokers who successfullyquit during the study.

Nicotine addiction is known to be associated withabnormalities in the dopamine system. But scientists areuncertain if smoking induces those abnormalities or if theyalready exist in some people and make them more vulnerable togetting hooked on nicotine.

"In case of a predisposing trait, abnormalities are expectedto persist with abstinence," Rademacher said. "Conversely, ifdopamine function normalizes with abstinence this ratherindicates that alterations were induced by substanceconsumption."

Overly preoccupied with drug use

Even so, the results are encouraging because they suggestthat brain function is plastic, or modifiable, and that anex-smoker's brain can return to more normal functioning overtime, said Joseph McClernon, a psychiatry researcher at DukeUniversity School of Medicine in Durham, North Carolina, whowasn't involved in the study.

"To the extent that smoking or other drug use alters howthis system functions normally can have impacts on behaviour thatincrease the likelihood that one continues to use drugs or hasdifficulty in quitting drug use," McClernon said.