When speed slows you down

Focuses on the effects of amphetamines on the human brain. Drugs' effects on the brain's parts.

By Marjorie Centofanti, published on February 01, 1997

You'd expect amphetamines--commonly known as "uppers" and"speed"--to rev up the entire brain at once. But a recent study shows that the drugs are in fact amazingly selective, boosting activity in some parts of our mind while actually calming other areas, according to Daniel Weinberger, Ph.D., a psychologist at the National Institute of Mental Health.

Weinberger and his calleagues gave amphetamines to eight men and women, then had them work on an abstract reasoning test that placed heavy demands on the prefrontal cortex, a part of the brain important for short-term memory. (You're using it to store what you've read of this article.) Later, the subjects were asked to shift to a task that used a different part of their brain, the hippocampus. All the while, the researchers were PET scanning the participants' brains to see which regions were most active.

Surprisingly, the drugs only enhanced activity in the brain area engaged in the task at hand--the prefrontal cortex, for example, in people working on the reasoning test. In the parts of the brain not being taxed, meanwhile, amphetamines acted like a wet blanket. So when Weinberger's subjects switched to the second task, their hippocampus lit up and their cortex calmed down. "This is probably what paying attention is all about," says Weinberger. The finding, moreover, could help explain a long-mysterious paradox: why Ritalin--a type of amphetamine widely prescribed for attention deficit disorder (ADD)--helps calm many kids with ADD instead of making them more hyperactive.