Reduced grey matter in frontal lobes linked to teenage smoking

Levels of grey matter in two parts of the brain may be linked to a desire to start smoking during adolescence and the strengthening of nicotine addiction, according to a new study published in the journal Nature Communications.

Grey matter is the brain tissue that processes information and contains all of the organ’s neurons. While brain development continues into adulthood, grey matter growth peaks before adolescence. Low grey matter volume in the left side of the ventromedial prefrontal cortex may be an ‘inheritable biomarker’ for nicotine addiction, according to the study authors — with implications for prevention and treatment.

The international team of scientists, led by the Universities of Cambridge and Warwick in the UK and Fudan University in China, analysed brain imaging data of over 800 young people gathered by the IMAGEN project from sites in four European countries: UK, Germany, France and Ireland. The researchers compared data for those who had smoked by age 14 with those who had not, and repeated this for the same participants at ages 19 and 23.

They found that, on average, teenagers who started smoking by 14 years of age had markedly less grey matter in a section of the left frontal lobe linked to decision-making and rule-breaking. Additionally, those who started smoking by age 19 also had less grey matter in their left prefrontal cortex at 14, indicating a potential causal influence.

The scientists also looked at the right ventromedial prefrontal cortex, which is linked to the seeking of sensations. Grey matter loss occurs in everyone as they age; however, those who smoked from age 14 as well as those smoking from age 19 both ended up with excessive grey matter loss in the right frontal lobe. 19-year-old smokers who did not start during adolescence had similar grey matter levels at age 14 to those who never smoked at all, suggesting that a rapid reduction in the right ventromedial prefrontal cortex only begins with the onset of smoking. Data at age 23 showed that grey matter volume in the right prefrontal cortex shrank at a faster pace in those who continued to smoke, suggesting an influence of smoking itself on prefrontal function.

The researchers argue that less grey matter in the left forebrain could lower cognitive function and lead to ‘disinhibition’: impulsive, rule-breaking behaviour arising from a limited ability to consider consequences. This may increase the chances of smoking at a young age. Once a nicotine habit takes hold, grey matter in the right frontal lobe shrinks, which may weaken control over smoking by affecting ‘hedonic motivation’: the way pleasure is sought and managed. Excessive loss of grey matter in the right brain was also linked to binge drinking and marijuana use.

Taken together, the team’s findings point to a damaged ‘neurobehavioural mechanism’ that can lead to nicotine use starting early and becoming locked into long-term addiction. As noted by co-senior author Professor Trevor Robbins, from Cambridge’s Department of Psychology, “In our study, reduced grey matter in the left prefrontal cortex is associated with increased rule-breaking behaviour as well as early smoking experiences. It could be that this rule-breaking leads to the violation of anti-smoking norms.”

Co-author Professor Barbara Sahakian, from Cambridge’s Department of Psychiatry, added, “The ventromedial prefrontal cortex is a key region for dopamine, the brain’s pleasure chemical. As well as a role in rewarding experiences, dopamine has long been believed to affect self-control.

“Less grey matter across this brain region may limit cognitive function, leading to lower self-control and a propensity for risky behaviour, such as smoking.”

The researchers also analysed data from two questionnaires completed by participants to investigate the personality traits of novelty seeking (including impulsiveness and rule-breaking) and sensation seeking (focused on pleasurable experiences). Less grey matter in the left prefrontal cortex was associated with novelty seeking, particularly disorderly and rule-breaking behaviour, while reduced grey matter volume in the right prefrontal cortex was linked to sensation seeking only.

“Less grey matter in the left frontal lobes is linked to behaviours that increase the likelihood of smoking in adolescence,” concluded lead author Professor Tianye Jia, from Fudan University.

“Smokers then experience excessive loss of grey matter in the right frontal lobes, which is linked to behaviours that reinforce substance use. This may provide a causal account of how smoking is initiated in young people, and how it turns into dependence.”

This is a modified version of a news item published by the University of Cambridge under CC BY-NC-SA 4.0. This version is similarly licensed under CC BY-NC-SA 4.0.

Image credit: iStock.com/urbazon