N.Y. This is the first time research has shown that methamphetamine doesn't just affect a brain chemical that passes along messages to cells but also does actual physical damage to the brain, say the researchers. But since doses for speed differ on the street than they do in the laboratory, researchers had yet to see the same effects on the human brain. To check whether speed was causing changes in the human brain, Volkow used chemical tags and brain scans to measure dopamine transporter levels and then gave motor control and mental ability tests to 15 people who had stopped taking speed. She then compared the findings with people who had never taken the drug.
Dopamine is linked to many functions and emotional responses.
Brain function tests showed a reduction in dopamine transporters, Volkow says. And what we also showed was that those losses are producing functional changes for motor tasks, which was not unexpected because dopamine controls movement. We also saw impairment in verbal learning and memory. In three subjects, we saw impairments a year later. A second test showed that speed affects other areas of the brain, Volkow says.