Alcohol Abuse Alters the Reward Circuit in Adolescent Brains

Science

A new study shows that alcoholism in adolescents is linked to an alteration of nerve fibers in the brainstem and a modification of the reward system. The adolescents concerned become hypersensitive to rewards, leading to fears of them being at greater risk of alcohol dependence in the long-term.

The consequences of binge drinking, which involves drinking a large quantity of alcohol in a short space of time, particularly during nights out, have been studied in 16-18 year-olds. But little attention had been paid to the effects of regular heavy drinking by younger subjects (around 14 years of age), probably due to the quite exceptional nature of such behavior at that age. However, André Galinowski, Jean-Luc Martinot and their colleagues from the Neuroimaging and Psychiatry* research unit (Gif-sur-Yvette) decided to explore the issue further.

They enrolled teenagers from the IMAGEN cohort, a European project intended to evaluate the influence of biological, psychological and environmental factors on brain development in adolescence. Out of the 1,510 teenagers having completed a questionnaire on their alcohol consumption at 14 years of age, 32 were found to have problematic consumption (AUDIT score equal to or greater than 7).

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The Alcohol Use Disorders Identification Test AUDIT, developed by the World Health Organization, is used to establish scores based on consumption level and habits. A score below 7 indicates low or insignificant risk (ordinary consumption). A score between 7 and 10 indicates problematic, high-risk consumption. Beyond that, alcohol dependence is likely.

The questionnaire was then completed again at 16 years of age, in which it was found that 34 additional teenagers, who were abstinent at 14 with an AUDIT score of 0, had in the meantime become major consumers (score >7). The researchers also selected 128 control adolescents, who were fully abstinent at both 14 and 16 years of age. Questionnaires and an interview with a psychiatrist excluded from the analysis young people with a family history of alcoholism, consumers of other types of drug, or those suffering from psychiatric disorders such as depression and schizophrenia.

The brain stem, target of the alcohol

The researchers analyzed brain images from all the participants, obtained by MRI at 14 and 16 years of age. They observed abnormalities in the 14-year-old problematic consumers, which were absent in the controls. These were located in the midbrain, the reptilian brain, a highly preserved region in species due to its involvement in essential vital functions: general energy, breathing, cardiac function, etc. Groups of neurons also irradiate from this zone to other regions of the brain, controlling the reward system in particular. This system reinforces motivation for actions or behaviors that activate it: when an individual can expect a reward following an action, they will be more inclined to perform that action. This reward can be material (a sum of money), or biological – with a release of endorphins that will procure a feeling of wellbeing.

Plaisir et Addiction (Pleasure and Addiction, only available in French) - educational video – 4 min – taken from the series POM Bio à croquer (2013)

The abnormalities observed in the midbrains of young alcoholics correspond to an alteration of the nerve fibers, particularly myelin – the substance that covers the fibers and promotes nerve conduction. "It can be deduced that the development of these fibers is disrupted in these teenagers", clarifies Martinot. What is more, tests have shown that these subjects are hypersensitive to rewards. They are more efficient than the control subjects when a reward in the form of candy is promised after the requested action. "This can lead to fears of hypersensitivity to the desire for the hedonistic effects of alcohol, maintaining the vicious circle of dependence in order to feel better", worries Martinot.

The researchers also found these same alterations in adolescents who had become alcoholics at the age of 16. They observed that slight abnormalities were already present in the same region when they were 14 years old and abstinent, suggesting a potential predisposition. "We had already found these midbrain alterations in adults who had overcome their dependence on alcohol. This new research confirms the effect of heavy drinking on the adolescent midbrain. Additional proof that prevention targeting the very beginning of adolescence needs to be stepped up", concludes the researcher.

Note:
*unit 1000 Inserm/Université Paris-Sud, Neuroimaging and Psychiatry team, Gif-sur-Yvette

Source : A Galinowski et coll. Heavy drinking in adolescents is associated with change in brainstem microstructure and reward sensitivity. Addiction Biology, juillet 2019. DOI: 10.1111/adb.12781