A new brain imaging study published in JAMA Psychiatry suggests that the high rate of relapse among smokers trying to quit may be due to an inability - brought on by nicotine withdrawal - to switch from the "default mode" brain network, to the "executive control" brain network.
The researchers, from the University of Pennsylvania in Philadelphia and the National Institute on Drug Abuse (NIDA) in Baltimore, MD, explain that when the default mode is engaged, people tend to be in so-called introspective or self-referential states.
Whereas engaging the executive control network helps them exert more conscious self-restraint over cravings, and focus on setting and achieving quitting goals.
According to the NIDA, 50 years ago the percentage of adult Americans who were regular smokers (42%) was more than twice what it is today (19%), something that can justifiably be claimed as a huge public health achievement.
But the pace of this decline seems to have stalled somewhat, and tobacco remains the leading preventable cause of disease and death in the US, where 8.6 million people have a smoking-related illness and more than 440,000 die from smoking-related causes every year.
The fact is, while fully recognizing the damage smoking inflicts on health, many smokers struggle to overcome nicotine addiction, and despite successful attempts to quit, they find themselves relapsing again and again.
This is why studies that can identify people at risk for persistent smoking, and offer clues about the underlying reasons, are going to be very useful in developing treatments that help this group give up the habit for good.
Study proposes a neurological basis for smoking relapse
In this latest study, the researchers propose a neurological reason that might explain why up to 80% of smokers trying to quit end up resuming the habit, depending on the type of treatment they get.
Using functional magnetic resonance imaging (fMRI) brain scans, the researchers found that smokers who abstained from cigarettes (i.e. in nicotine withdrawal) showed weaker connections between certain networks in their brains - the default mode network, the executive control network and the salience network.
They propose that it is these weakened connections that reduce their ability to shift to or allow influence to come mostly from the executive control network, which would otherwise help them strengthen their resolve and maintain their ability to resist cravings for cigarettes.
Lead author Dr. Caryn Lerman, of the University of Pennsylvania's new Brain and Behavior Change Program, says:
"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."
For their study, Dr. Lerman and colleagues took fMRI brain scans of 37 healthy people aged 19 to 61 who smoked 10 or more cigarettes a day. They took two sets of scans: one set 24 hours after not touching a cigarette (the abstinence state), and another set after smoking as usual (the sated state).
Smokers' brain connections were significantly weaker in abstinence
The brain scans taken during the abstinence state showed significantly weaker connections between the salience network and the default mode network, compared with those taken during the sated state.
The researchers also found that weakened connectivity during the abstinence state was linked with reported increases in withdrawal symptoms, smoking urges and negative moods. They suggest this means weaker inter-network connectivity may be why some people struggle to quit smoking.
Although previous studies have examined how nicotine affects brain connections in the resting state - that is, when no specific goals are in play - this is the first to compare resting brain connectivity in an abstinent state with when people are smoking as usual, and then link those differences to symptoms.
Dr. Lerman says the study offers a neurological explanation for what is going on in the brain when quitting smokers experience symptoms of withdrawal.
"The next step will be to identify in advance those smokers who will have more difficultly quitting and target more intensive treatments, based on brain activity and network connectivity," she says, explaining that:
"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."
In April 2013, Medical News Today reported a study that found magnetic brain stimulation may help smokers quit. The researchers said a single 15-minute session temporarily reduced cue-induced smoking craving in nicotine-dependent individuals.