High relapse rate in smokers may be explained by diminished connectivity among key brain networks, researchers said.
The findings help validate a neurobiological basis behind why so many people trying to quit end up relapsing - up to 80 per cent, depending on the type of treatment - and may lead to new ways to identify smokers at high risk for relapse who need more intensive smoking cessation therapy, they said.
The brain imaging study shows how smokers suffering from nicotine withdrawal may have more trouble shifting from a key brain network - known as default mode, when people are in a so-called "introspective" or "self-referential" state - and into a control network, the so-called executive control network, that could help exert more conscious, self-control over cravings and to focus on quitting for good.
Scientists found that smokers who abstained from cigarettes showed weakened interconnectivity between certain large-scale networks in their brains: the default mode network, the executive control network, and the salience network.
They said this weakened connectivity reduces smokers' ability to shift into or maintain greater influence from the executive control network, which may ultimately help maintain their quitting attempt.
"What we believe this means is that smokers who just quit have a more difficult time shifting gears from inward thoughts about how they feel to an outward focus on the tasks at hand," said Caryn Lerman from the University of Pennsylvania.
"It's very important for people who are trying to quit to be able to maintain activity within the control network - to be able to shift from thinking about yourself and your inner state to focus on your more immediate goals and plan," said Lerman.
This is the first study to compare resting brain connectivity in an abstinent state and when people are smoking as usual, and then relate those changes to symptoms of craving and mental performance, researchers said.
Researchers conducted brain scans on 37 healthy smokers (those who smoke more than 10 cigarettes a day) ages 19 to 61 using functional magnetic resonance imaging (fMRI) in two different sessions: 24 hours after biochemically confirmed abstinence and after smoking as usual.
Imaging showed a significantly weaker connectivity between the salience network and default mode network during abstinence, compared with their sated state.
Weakened connectivity during abstinence was linked with increases in smoking urges, negative mood, and withdrawal symptoms, suggesting that this weaker internetwork connectivity may make it more difficult for people to quit.
The findings appear in the journal JAMA Psychiatry.