Changes in the brain that happen when someone quits smoking can help predict which individuals will be successful in swearing off the habit and which ones might start smoking again, researchers have found.

In a study at the University of Pennsylvania School of Medicine, MRI scans were made of people aged 18 to 65 who had been smoking in excess of 10 cigarettes daily for 6 months.

Two scans were made of each study participant, one immediately after smoking and a subsequent one 7 days after they started an attempt to quit.

"The vast majority of people who relapse [do so] within the first seven days," says Penn professor of psychiatry Caryn Lerman. "When we look at the original sample of 80 people, 19 of them were able to make it the entire seven days ... that's 75 percent who couldn't make it."

The MRI scans revealed that those in the study who displayed decreased activity in the brain's dorsolateral prefrontal cortex -- a region fundamental in cognitive function, goal-directed behavior and working memory -- were the most likely to start smoking again, the researchers reported in the journal Neuropsychopharmacology.

That decrease in activity was linked to an increase in another area of the brain, the posterior cingulate cortex, a portion unrelated to goal achievement.

The effect -- a decrease in activity in the one region and increased activity in the other -- is the opposite of what the brain requires to be successful in achieving a goal, says Lerman, who heads the university's Center for Interdisciplinary Research on Nicotine Addiction.

"What we really want to have going on in the brain [for success] is a combination of increased activity planning, goal directiveness and cognitive control, and suppression in the part of the brain involved in rumination and thinking about self and non-goal-related thought," she says.

"So stopping smoking itself makes it more difficult to stay off cigarettes -- [it] compromises exactly those processes that you need to be successful," Lerman says.

Most people who attempt to kick the habit can't get beyond 24 hours before they're back to smoking, Lerman notes.

The success rate for people giving up smoking on any given attempt is only 4 to 7 percent, according to the American Cancer Society.

Lerman admits it wouldn't be practical to conduct a brain scan on every smoker expressing a desire to quit, but suggests as technology advances a battery of tools -- cognitive analysis, brain scans and genetic testing -- could be developed to would offer an improved prediction value that could lead to customized treatment offering a better chance of success for someone wanting to quit smoking.