A new study from Yale suggests that drug addiction should be thought of as a developmental disorder, because the changing circuitry of teenagers brains appears to leave them especially vulnerable to the effects of drugs and alcohol. Dr. R. Andrew Chambers of the Yale School of Medicine, lead author of the article: said addictive drugs worked by stimulating parts of the brain that are changing rapidly in adolescence. In particular, Dr. Chambers said, the drugs tap into a neural imbalance that may underlie teenagers affinity for impulsive and risky behaviour. The circuitry that releases chemicals that associate novel experiences with the motivation to repeat them develops far more quickly in adolescence than the mechanisms that inhibit urges and impulses. As a result he said, teenagers are not only more likely to experiment with drugs than other groups, but the experience also has more profound effects on the brain – and sometimes permanent ones. The article, published in the June issue of The American Journal of Psychiatry, was based on a review of 140 earlier studies. Dr. Chambers wrote that although it had long been known that most addicts began using drugs in adolescence, most research into the mechanisms of addictions or treatment focused on adults.

Shifting to a model that links vulnerability to normal developmental changes in the brain could lead to new methods of prevention or ways of singling out teenagers at higher risk for drug use, he said. Dr. Chambers acknowledged that social factors appeared to play a role in drug addiction but said they did not account entirely for greater levels of drug use among adolescents. His analysis covered three aspects of teenage behaviour and their basis in brain functioning – attraction to novelty, less than adult levels of judgment and an overriding interest in sex. Teenagers are drawn to new activities and experiences, a process that Dr. Chambers referred to as “the expansion of their motivational repertory.” “That’s a good thing.” he said, “because adolescents have to earn how to be adults.” But to aid the process, the motivational circuitry of the brain – the complex of chemical reactions that make certain experiences more desirable than others – is also rapidly expanding. It is this circuitry, centred on the chemical dopamine, that is at the heart of the addictive effects of a wide range of drugs as different as cocaine and alcohol, Dr. Chambers said.

At the same time the parts of the frontal cortex that are activated by adults when they weigh risks and rewards lag developmentally. You have a situation where the motivational brain areas are particularly active,” Dr. Chambers said, “and the part of the brain that is supposed to inhibit impulses is not working well, because it is sort of under construction.” The other port of the equation lies in a number of brain regions that are reshaped in adolescence as they respond to soaring levels of sex hormones, Dr. Chambers said that rapid change seemed to leave young people unusually attuned to all sorts of new social and sexual stimulation, which in turn appeared to make the brain more open to the addictive effect of drugs.