Researchers from Duke University Medical Center have used brain PET scans to identify three regions of the brain that seem to control nicotine dependence and craving.

The affected regions include the thalamus, which controls sensory input and may be related to the inability to focus and feeling of being overwhelmed often experienced during withdrawal; the straitum, also know as the brain's pleasure center; and the anterior cingulate cortex, which is involved in cognitive functions like conflict resolution, self-regulation, decision making, and emotion.

"If you can't calm down, can't derive pleasure and can't control yourself or concentrate, then it will be extremely difficult for you to break the habit," said lead study researcher Jed E. Rose, Ph.D., director of the Duke Center for Nicotine and Smoking Cessation Research. "These brain regions may explain why most people try to quit several times before they are successful."

The study was published online in the journal Neuropsychopharmacology.

The research was funded by tobacco company Philip Morris USA.