Brain circuit that supports smoking cessation identified.

It is known that smoking is one of the leading causes of preventable death globally.  Diseases related to tobacco smoking have been shown to kill approximately half of long-term smokers when compared to average mortality rates faced by non-smokers.  Stopping smoking has huge benefits and it’s never too late to give up, however, quitting can be extremely difficult due to the highly addictive properties of tobacco and its casing.  Now, a study from researchers at the Medical University of South Carolina (MUSC) shows that success is more likely with strong communication between parts of the brain that inhibit and execute automated behaviour.  The team state their study is the first to link the strength of communication in a brain circuit that inhibits automated behaviour with the ability to resist smoking.  The study is published in JAMA Psychiatry.

Previous studies show that in the brain, smoking becomes automated.  One way the brain has been shown to inhibit automated behaviour is through a pathway called the inhibitory control network, which starts in the right inferior frontal gyrus and travels through the prefrontal cortex to the thalamus. Communication through this pathway is often disrupted in the brains of smokers. The current study investigates whether this pathway is involved when smokers attempt to quit.

The current study examines the inhibitory control networks in the brains of 81 nicotine-dependent adults committed to a 10-week smoking cessation program. The researchers used fMRI to monitor brain activity while patients perform a task of inhibitory control. The patients were instructed to strike a computer key each time a coloured circle appeared on screen, and to not strike the keyboard when a  rare circle of a certain colour appeared. Results show that when a higher blood oxygenation level-dependent (BOLD) response in the inhibitory control circuit is exhibited, the brain is using more resources to inhibit the automatic response of striking the key when the rare circle appears.

The group state that after 10 weeks, approximately half of the smokers had quit successfully. Data findings show that the smokers who successfully quit had lower BOLD responses in their inhibitory control networks before trying to quit.  Results show that the successful quitters’ BOLD responses were lower in the right inferior frontal gyrus and right thalamus, they also had stronger functional connections between those regions. The lab observed that the patients who relapsed had scored just as well on the inhibition control task as those who quit successfully, however, it seemed that their automated behaviour may have required more effort to inhibit.

The team then investigated BOLD responses in smokers who had not committed to quitting.  The group measured BOLD signals in 26 smokers performing the same task; each person was then presented with an open pack of their preferred brand of cigarettes, a lighter, and an ashtray. They were paid one dollar for every six minutes they did not smoke as a small incentive for an hour.  The lab note that in general, the lower the BOLD response during the task of inhibitory control, the longer the person resisted smoking. They go on to add that the smokers who resisted temptation longer also had stronger functional connections in their inhibitory control networks.

The team surmise their findings show that corticothalamic circuitry function during inhibitory control is associated with smoking relapse vulnerability. They go on to add that they identify neurobiological mechanisms which are fundamental to learning new behaviours and also to stopping those that become automated, such as smoking.  For the future, the researchers are evaluating the potential of certain behavioural and pharmacological treatments that could strengthen communication in the inhibitory control pathway of people who smoke.

Source: Medical University of South Carolina (MUSC)

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