August 18, 2023: Grey matter in the human brain may be linked to the start of adolescent smoking and nicotine addiction — a study that may have implications for prevention and treatment.
A team of scientists, led by the universities of Cambridge and Warwick in the UK and Fudan University in China, analysed brain imaging and behavioural data of over 800 young people at the ages of 14, 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.
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, the researchers said.
In addition, the scientists found that the right part of the same brain region also had less grey matter in smokers.
‘Seeking of sensations’
“Importantly, loss of grey matter in the right prefrontal cortex appears to speed up only after someone has started smoking. This region is linked to the seeking of sensations,” according to the researchers.
The team stated 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.
The findings point to a damaged “neurobehavioural mechanism” that can lead to nicotine use starting early and becoming locked into long-term addiction, the researchers wrote in an article published in the journal Nature Communications.
“Smoking is perhaps the most common addictive behaviour in the world and a leading cause of adult mortality,” said Prof Trevor Robbins, co-senior author from Cambridge’s Department of Psychology.
“The initiation of a smoking habit is most likely to occur during adolescence. Any way of detecting an increased chance of this, so we can target interventions, could help save millions of lives.”
Annual deaths from cigarettes are expected to reach eight million worldwide by the end of the decade. Currently, one in five adult deaths each year is attributed to smoking in the US alone.
“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,” said Robbins.
Limit cognitive function
Co-author Prof Barbara Sahakian from Cambridge’s Department of Psychiatry said: “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 study used data gathered by the IMAGEN project from sites in four European countries such as the UK, Germany, France, and Ireland.
The researchers compared brain imaging 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.
Those with smoking experience by 14 years of age had significantly less grey matter in the left prefrontal cortex, on average.
Excessive grey matter loss
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.
Grey matter loss occurs in everyone as they age. 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.
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 tobacco epidemic is one of the biggest public health threats the world has ever faced, killing more than eight million people a year around the world. More than seven million of those deaths are the result of direct tobacco use while around 1.3 million are the result of non-smokers being exposed to second-hand smoke, according to the WHO.