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Researchers identify brain circuit that helps people quit smoking

March 01, 2017
Dr. Brett Froeliger speaks to a team member
Dr. Brett Froeliger says his team's research may help scientists understand why some smokers have a harder time quitting than others. Photo by Brennan Wesley

Quitting smoking is hard. Addiction experts at MUSC Hollings Cancer Center have identified a circuit in the brain that could help. It seems that people who have stronger communication in this circuit are more likely to successfully quit smoking. Brett Froeliger, Ph.D., an addiction scientist in the MUSC Department of Neuroscience and Hollings Cancer Center, helped lead the research and published the results in the new issue of JAMA Psychiatry

Smoking becomes an automated behavior over time. In the brain, the urge to smoke begins the same way your foot automatically moves to the gas pedal when a red stoplight turns green. “A pack-a-day smoker places a cigarette in their mouth a few hundred times a day over years, so they have many trials of experience,” said Froeliger. “It becomes automated.”

a hand holds a cigarette against a black background as smoke wafts into the air
Photo illustration by Sarah Pack

This kind of automated physical behavior is stopped by a circuit in the brain called an inhibitory control network, which includes the prefrontal cortex and the thalamus. Brain function within this circuit is often disrupted in the brains of smokers. 

Froeliger wanted to know if this pathway was involved when smokers attempted to quit. While working in the laboratory of Joseph F. McClernon, Ph.D., at Duke University, Froeliger and McClernon examined inhibitory control function in the brains of 81 nicotine-dependent adults committed to trying a 10-week program to help them quit smoking. 

Before the program started, the researchers used functional MRI to monitor blood oxygenation level-dependent response, or BOLD, signals in the inhibitory control network. The patients were instructed to strike a computer key each time a colored circle appeared on screen, except on the rare occasion when a circle of a certain color appeared. A higher BOLD response meant that the brain was using more resources to inhibit the automated response of striking the key when the rare circle appeared.

Dr. Brett Froeliger speaks to a patient about to go into an MRI machine.
Dr. Froeliger, right, says technology can play an important role in finding new ways to help people fight addiction. Photo by Brennan Wesley

After 10 weeks, about half of the smokers had quit successfully. It turned out that they had lower BOLD responses during the task and stronger functional connectivity in their inhibitory control networks before they had tried to quit. Patients who relapsed had scored just as well on the task as those who quit successfully. It seemed that their automated behavior may have required more effort to inhibit. 

Froeliger continued his work with a new twist when he joined the MUSC Hollings Cancer Center. He wondered if the same thing happened to smokers who had not committed to quitting. The group measured BOLD responses in 26 smokers performing the rare circle task. This time, however, each person was then given an open pack of their brand of cigarettes, a lighter, and an ashtray. They were paid one dollar for every six minutes they did not smoke, up to an hour. The idea was to give each person a small perk to resist the urge to smoke. 

Similar to the first finding, the lower a person’s BOLD response, the longer the person resisted smoking. Those who resisted temptation longer also had stronger functional connectivity in their inhibitory control networks. 

This study is the first to link the ability to resist smoking with strength of a brain circuit that inhibits automated behavior. Therapies that support this pathway could help smokers who are trying to quit. The research adds to the evidence showing that differences in biology can help explain why some people who are trying to resist smoking have more success than others. 

“This work helps scientists understand why some smokers have a harder time quitting,” said Froeliger. “Individual differences in brain biology are important.”