Using brain scans to test reaction times, the researchers showed 18- to 24-year-old college students either an X or an O on a screen and instructed them to press, as quickly as possible, a left button if an X appeared or a right button if an O appeared. If a tone was heard, they were instructed not to press a button.
Dr. Martin Paulus, a professor of psychiatry and colleagues, say the brain differences are believed to represent an internal hard wiring that may make some people more prone to drug addiction later in life.
“If you show me 100 college students and tell me which ones have taken stimulants a dozen times, I can tell you those students’ brains are different,” Paulus says in a statement. “Our study is telling us, it’s not ‘this is your brain on drugs,’ it’s ‘this is the brain that does drugs.’”
Occasional drug users were defined as having taken stimulants an average of 12 to 15 times. The “stimulant naive” control group included students who had never taken stimulants. Both groups were screened for factors, such as alcohol dependency and mental health disorders, that might have confounded the study’s results.
The findings, published in the Journal of Neuroscience, showed occasional users have slightly faster reaction times, suggesting a tendency toward impulsivity.
The most striking difference occurred during the “stop” trials. The occasional users made more mistakes, and their performance worsened, relative to the control group, as the task became harder.
“We used to think that drug addicts just did not hold themselves back but this work suggests that the root of this is an impaired ability to anticipate a situation and to detect trends in when they need to stop,” lead author Katia Harle, a postdoctoral researcher in the Paulus laboratory says.