THURSDAY, May 30, 2002 (HealthDayNews) -- An experiment with monkeys' brains may explain why some people suffer obsessions and addictions.
The answer appears to lie in the anterior cingulate cortex, a brain center involved in motivation and performance, says a report in tomorrow's issue of Science. Specific clusters of nerve cells in that center changed their activity as the monkeys got closer to being rewarded for completing a set of tasks.
It's possible flaws in this reward nexus make people vulnerable to obsessive-compulsive disorder -- in which they redouble their efforts or thoughts about problems uselessly -- or to drugs that heal the hurt, says Dr. Barry J. Richmond, a researcher in the National Institute of Mental Health Laboratory of Neurophysiology. He did the study with Munetaka Shidara of the Japanese National Institute of Advanced Industrial Science and Technology.
The scientists put electrodes into the brains of monkeys who were trained to press and release a bar in response to different-colored shapes on a computer screen. If they matched correctly, they were rewarded with drops of juice. Sometimes a colored bar at the top of the screen got brighter as they neared the reward, and sometimes the bar changed color at random.
When the bar showed the monkeys were nearing the goal, they made fewer mistakes. When the bar changed randomly, the number of mistakes did not change. The wiring of the monkeys' brains was so precise the scientists could observe changes in the activity of just a few dozen brain cells.
Some of the cells -- exactly 33 of them -- became more active as the monkeys saw the goal was near, but not when the random signals were flashed. It is the activity of these nerve cells that could provide at least a partial explanation for obsessive-compulsive disorder and drug addiction, Richmond says.
"Let's assume you had a signal like this, and it was turned up too high," he says. "It might make you feel like you had to be trying harder, telling you just go on a little further and you'll get satisfied. Our speculation is that this signal never resolves for conditions like obsessive-compulsive disorder. Or, in the case of addiction, a drug has the effect of satisfying the signal."
Brain imaging studies have shown that abnormalities in the anterior cingulate cortex are implicated in a number of disorders of emotion and action, such as obsessive-compulsive disorder and drug addiction, says Laura L. Peoples, an assistant professor of psychology at the University of Pennsylvania, who wrote an accompanying commentary. The new study is another indicator that public attitudes -- and policy -- toward drug addiction needs adjustment, she says.
"Many people in the general public view addicts as individuals who are ethically or morally weak, people who choose not to control their behavior," Peoples says. "But the anterior cingulate cortex and other cortical regions are areas that appear to be damaged in drug addicts. These regions are critically involved in mediating conscious control. So, the very brain regions they need to control their behavior aren't functioning properly."
The same appears to be true of obsessive-compulsive disorder and some related conditions, Peoples says, but in the case of drug addiction the law comes into the picture.
"This suggests that a person who is addicted should be treated for a medical illness, rather than being punished," she says. "Putting someone in jail isn't going to work when the brain centers aren't working properly."
What To Do
You can learn more about obsessive-compulsive disorder from the Obsessive-Compulsive Foundation or the National Institute of Mental Health. Learn more about drug problems from the National Institute on Drug Abuse.
