New research suggests that there is a complex networks of neurons in some youngsters’ brains that make them more likely to begin smoking, experimenting with cannabis or consuming large amounts of alcohol.
Scientists used MRI (magnetic resonance imaging) scans to highlight abnormalities by comparing the brains of almost two thousand 14 year olds. It is the first time the vast and chaotic actions of a teenage brain at work have been shown in such detail.
The findings, published online in Nature Neuroscience, helps answer a longstanding question about whether certain brain patterns come before drug use, or are caused by it. Psychiatrist Professor Hugh Garavan, of the University of Vermont in New England, said, “The differences in these networks seem to precede drug use.”
Researchers find that diminished activity in a network involving an area known as the orbitofrontal cortex which is involved in decision making was linked with experimentation with alcohol, cigarettes and illegal drugs in early adolescence. Co author Dr Robert Whelan said “these networks are not working as well for some kids as for others,” making them more impulsive.
Using a complex mathematical formula, the researchers were able to find seven networks involved when impulses were successfully inhibited and six others when inhibition failed. Dr Whelan said these networks “lit up” when participants were asked to perform a repetitive task involving pushing a button on a keyboard, but were then able to successfully stop - or inhibit - the act in mid-flow. Those with better inhibitory control were able to succeed faster.
But the underlying networks behind these tasks could not have been detectable in a typical scanner study of about sixteen or twenty people. Dr Whelan said, “This study was orders of magnitude bigger, which lets us overcome much of the randomness and noise - and find the brain regions that actually vary together.”
Prof Garavan said faced with a choice about smoking or drinking, the 14 year old with a less functional impulse-regulating network will be more likely to say, “ ‘yeah, gimme, gimme, gimme!’, and this other kid is saying, ‘no, I'm not going to do that.’” He said testing for lower function in this and other brain networks could one day be used by researchers as “a risk factor or biomarker for potential drug use.”
The researchers were also able to show other newly discovered networks are connected with the symptoms of attention-deficit hyperactivity disorder (ADHD). These are distinct from those associated with early drug use. Both ADHD and early drug use are associated with poor inhibitory control. But the new research shows these apparently related problems are regulated by different networks in the brain - even though both groups of teens can score poorly on tests of their “stop-signal reaction time,” a standard measure of overall inhibitory control used in studies such as this.
Addiction expert Prof Edythe London, of the University of California, Los Angeles, who was not part of the study, described it as “outstanding.” She said the work “substantially advances our understanding of the neural circuitry that governs inhibitory control in the adolescent brain.”
Prof Garavan said, “The take-home message is that impulsivity can be decomposed, broken down into different brain regions, and the functioning of one region is related to ADHD symptoms, while the functioning of other regions is related to drug use.”
Led by Professor Gunter Schumann at the Institute of Psychiatry, King's College London, Imagen has carried out neuroimaging, genetic and behavioural studies of teenagers in Ireland, England, France and Germany. It will continue to follow the progress of the teenagers for several years, investigating the roots of risk-taking behaviour.
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