Smokers know dangers but do not quit
By Ruth SoRelle, M.P.H.
Most smokers know their habit is bad for them. Yet they continue to light up.
The secret lies deep within their brains, said researchers from Baylor College of Medicine in a report in the journal Nature Neuroscience.
For most people, the threat of harm from smoking or other negative habits is enough, but smokers ignore those "fictive" signals, said P. Read Montague, Ph.D., professor of neuroscience at BCM and director of Its Brown Human Neuroimaging Laboratory.
Potential outcomes affect choices
In most people, "fictive" outcomes play a "dominant role in the choices we make," said Montague. "The brain computes signals that evaluate unexperienced possibilities, both positive and negative, and then guide us into our actions. It's these fictive guidance signals that keep us from becoming purely reward harvesting machines in the way that addicts are."
Testing outcomes
To study the differences between chronic smokers and people who do not smoke, Montague and his colleagues used an investment game and functional magnetic resonance imaging (fMRI). The game allowed them to determine how members of each group responded to a "what if" outcome.
When subjects play the investment game, they invest money in a stock market. They are then told what their profits were and the maximum amount they could have made. The researchers found that for nonsmokers, the most important influence on the next investment was "what could have happened" on the last round. However, even though smokers' brains recognized what could have happened in the previous round (as shown in the fMRI results), their next actions were based primarily on the actual rewards they received.
Smokers don't act
"The brain's might-have-been signal in smokers is identical to nonsmokers, but the smokers don't act on it," said Terry Lohrenz, Ph.D., a fellow and instructor in BCM's Computational Psychiatry Unit and one of the report's authors. "We think that in smokers, the parts of the brain that react to these fictive signals may be impaired. There's an imbalance between acting on immediate rewards and acting on fictive outcomes, and the smokers are led almost completely by the immediate actual rewards."
Forgoing good health
The authors' findings fit with the fact that addicts – including smokers – continue drug use and pursue addictive behaviors even though they know that it may have devastating effects and that they are forgoing good health.
"Using this game, we can quantitatively measure a person's response to fictive outcomes, and we think the findings have significant implications for understanding and treating addiction," said Pearl Chiu, Ph.D., first author on the paper and assistant professor in BCM's Computational Psychiatry Unit. "Improving the recognition of 'what might happen' could be a focus of cognitive behavioral therapies, and neurofeedback might target brain systems that strengthen the impact of fictive outcomes on addicts' behavior."
The researchers wrote in their paper that "these findings are consonant with the emerging understanding of addiction at the molecular level, and the computational model-based approach implemented here facilitates a mechanistic understanding of continued drug use in the presence of potential negative consequences and foregone positive outcomes."
Funding for this research came from the Kane Family Foundation, the National Institute on Drug Abuse, the National Institute of Neurological Disorders and Stroke, the Angel Williamson Imaging Center, and the American Psychological Association.
