Parts of the brain involved in monitoring behaviors and emotions show different levels of activity in cocaine users relative to non-drug users, even when both groups perform equally well on a psychological test.
These results - from a brain-imaging study conducted at the U.S. Department of Energy's Brookhaven National Laboratory and published online the week of May 25, 2009, by the Proceedings of the National Academy of Sciences - suggest that such impairments may underlie addictive vulnerability, and that treatments aimed at improving these functions could help addicted individuals resist drugs.
"Many studies have found decreased brain activity in drug-addicted individuals relative to healthy control subjects during psychological tests," said lead author Rita Goldstein, a psychologist at Brookhaven Lab. "But it's never been clear if these differences were due to varying levels of interest or ability between the two groups. This is the first study to look at two groups matched for performance and interest - and we still see dramatic differences in the brain regions that play a very significant role in the ability to monitor behavior and regulate emotion, which are both important to resisting drug use.
"Whether these brain differences are an underlying cause or a consequence of addiction, the brain regions involved should be considered targets for new kinds of treatments aimed at improving function and self-regulatory control," Goldstein said.
The researchers studied 17 active cocaine users and 17 demographically matched healthy control subjects. Both groups were trained to push one of four colored buttons corresponding to the color of type used to present words that were either related to drug use (e.g., crack, addict) or neutral household terms. Subjects were given monetary rewards for fast, accurate performance - up to 50 cents for each correct answer on some tests, for a maximum of $75.
After training, both groups performed equally well on this same test while lying in a magnetic resonance imaging (MRI) scanner, with performance improving when they knew they'd be earning the highest monetary reward. During the tests, the scientists used functional MRI (fMRI) to indirectly measure the amount of oxygen being used by specific regions of the brain, as an indicator of brain activity in those regions.
There were three main differences between the cocaine-addicted subjects and the healthy controls: