The Origins of Addiction
Unraveling the Differences between Young Smokers and their Ability to Quit
By Katherine Hill
Edited by: Sienna Schaeffer, Katie Kelly, and Jeff Stolley
Despite the overwhelming evidence for how harmful tobacco use is, there are approximately 46 million adult smokers in the United States (1). Fortunately, 70% of current smokers would like to quit (2). Unfortunately, the addictive nature of smoking can make quitting extremely difficult. In order to maximize ex-smokers’ chances of success, it is essential that we understand the reasons why people smoke and how to best help them quit.
One promising line of inquiry is how individual differences can affect a person’s ability to successfully stop smoking. Some evidence has suggested that genetics may play a role. One study found that individuals with certain versions of a nicotine receptor gene are more successful at quitting than individuals with other versions of the gene (1). In the future, a genetic test could be performed to determine whether smokers have a good chance of quitting on their own or should be given medication to help improve their chances of success.
In order to understand why some individuals are more successful at quitting than others, it is also important to understand what exactly is happening inside the brain that makes smoking so addictive. One hypothesis is that drug addiction simultaneously strengthens the pathways in the brain responsible for drug cravings and weakens the pathways in the brain that make everyday activities pleasurable (3). This means that addicts find drugs more enjoyable than non-addicts and other activities less enjoyable than non-addicts, so the reward for using drugs relative to other activities is much higher for people who are addicted to drugs.
Recently, a team of researchers expanded on this hypothesis by examining these reward pathways in young smokers. The researchers had previously performed several studies that monitored both the brain waves and specific brain regions of smokers when they were exposed to different kinds of stimuli. The scientists found that smokers who show higher emotional arousal to cigarette stimuli than to pleasant stimuli were less likely to be able to abstain from smoking for six months when compared to smokers who showed higher emotional arousal to the pleasant stimuli than to the cigarette stimuli.
As interesting as this finding was, the study was not designed to determine whether the different patterns of arousal caused the smoking or the smoking caused the brain pattern. It is possible that some of the participants were less stimulated by pleasant cues before they smoked which made them more likely to begin smoking or less likely to stop. It is also possible the participants found enjoyable stimuli more rewarding before they began smoking and that the smoking itself decreased their response to pleasant cues. In addition, the study only examined older smokers, whereas most smokers first become addicted in adolescence, meaning it was impossible to know at what point the different types of brain response appeared among this sample of smokers (4).
The researchers began to answer some of these questions by performing a similar experiment with smokers age 18–25. The participants viewed 60 pictures that showed either pleasant, unpleasant, neutral, or cigarette-related pictures. While the participants viewed the photos, their brain activity was monitored using an electroencephalogram (EEG), which is a device that can detect electrical activity in the brain. In this experiment, the EEG monitored a specific type of brain wave, called the Late Positive Potential (LPP), which corresponds with emotional arousal. That means that participants who had larger LPPs in response to a photo were more emotionally stimulated by that photo.
After collecting the data, the researchers used a computer program that separated the participants into two groups. The researchers did not tell the program how to group the participants. Instead, the program considered all of the data that was collected and attempted to create groups in such a way that the people in each group were as similar to the other people in the same group, and as different from the people in the other group, as possible.
When the researchers examined the groups that the computer created, they found that one group had higher emotional arousal in response to cigarette pictures than to pleasant pictures and the other group showed higher arousal in response to pleasant pictures than to cigarette pictures. The results dovetailed with those of previous studies that examined older smokers. The pattern was mainly driven by a difference in arousal to the pleasant pictures, which had also been noted in previous studies. This means that while both groups had a similar level of response to cigarettes, one group had a much larger response to the pleasant cues than did the other group.
The results were significant because they demonstrated that decreased response to pleasant stimuli is either present before someone begins smoking or develops quickly afterward. While the experiment still did not definitively answer the question of whether the brain pattern causes smoking or smoking causes the brain pattern, by showing that the pattern develops early on in smokers, it did make it easier to design future studies that can determine which way the causal arrow points.
The experiment also provided further evidence that LPPs are an effective way to measure sensitivity to drug-related and natural stimuli. Some researchers believe that decreased sensitivity to everyday rewards increases the likelihood that someone will smoke. Unfortunately, sensitivity has been difficult to study because there is no objective way to measure it.
In the future, LPPs could provide that objective measure. Researchers already knew that LPPs were associated with emotional arousal. Now that researchers have found consistent LPP patterns across several different studies and have demonstrated that smokers can be grouped into separate categories based on their LPPs, researchers may begin to view LPPs as a tool to study sensitivity to reward, rather than just as an interesting phenomenon. With the help of LPPs and other biological measures, scientists may be able to unravel the mechanisms that make some people more vulnerable to tobacco addiction than others.
An even more exciting, although much more tentative, use for LPPs could be to identify young smokers who are at high risk of becoming addicted so that targeted interventions could be used to end their cigarette use before it begins to escalate. Unfortunately, much more research is needed before that day comes.
Although this experiment was in many ways preliminary, it provides a direction for future research to examine the individual differences that make some people more likely to begin using cigarettes and less likely to stop. If later experiments show that LPPs can also be used as a measure of addiction sensitivity toward opiates or other drugs, they could prove to be even more valuable to addiction researchers. With the help of LPPs and other new techniques, scientists may be able to isolate the variations in nicotine receptors and other genes that render some people more vulnerable to addiction than others.
If we care about the well-being of the 46 million smokers in this country and about giving them every tool possible so that they can become ex-smokers, we need to make sure that current research studies mark the beginning, rather than the end, of the investigation into the reward pathways associated with smoking.
Sources
1. Odds of quitting smoking affected by genetics. National Institutes of Health (NIH) (2015). Available at: https://www.nih.gov/news-events/news-releases/odds-quitting-smoking-affected-genetics. (Accessed: 11th December 2016)
2. Health, C. O. on S. and. Smoking and Tobacco Use; Fact Sheet; Fast Facts. Smoking and Tobacco Use Available at: http://www.cdc.gov/tobacco/data_statistics/fact_sheets/fast_facts/. (Accessed: 11th December 2016)
3. Volkow, N. D., Koob, G. F. & McLellan, A. T. Neurobiologic Advances from the Brain Disease Model of Addiction. New England Journal of Medicine 374, 363–371 (2016).
4. Engelmann, J. M., Versace, F., Gewirtz, J. C. & Cinciripini, P. M. Individual differences in brain responses to cigarette-related cues and pleasant stimuli in young smokers. Drug and Alcohol Dependence 163, 229–235 (2016).
