The danger of
Stimulant drugs damage the brain’s decision-making
abilities, revving up the course of addiction and making it
harder for people to quit, research suggests.
BY SADIE F. DINGFELDER • Monitor staff
Stimulant drug abuse packs a triple-whammy to people’s decision-making abilities, hampering their reasoning and increasing impulsive and compulsive behaviors, according
to research presented at APA’s 2011 Annual Convention by
Trevor W. Robbins, a behavioral and clinical neuroscientist at
the University of Cambridge in England.
These three tendencies all have slightly different origins in the
brain, he said, but they all contribute to the story of stimulant
drug addiction — clouding people’s judgment during the early
stages of addiction, and then making it harder for them to quit.
“These drug abusers ... have poisoned their frontal cortex
and produced decision-making deficits,” Robbins said.
During the early stages of stimulant use, people often make
a bad bet — underestimating the number of times they can
use cocaine, for example, before becoming dependent. This
tendency may be explained in part by the fact that stimulant
drug use itself makes people worse gamblers, according
to one study by Robbins and his colleagues, published in
Neuropsychopharmacology (Vol. 2, No. 4).
In the study, the researchers asked four groups of
participants — 18 chronic amphetamine users, 13 opiate users,
10 people with orbitofrontal cortex lesions and 10 people with
dorsolateral or medial prefrontal cortex lesions — to play a
computer game known as the Cambridge Gambling Task. In
the game, the computer presents participants with an array
of 10 red and blue boxes, and asks them to guess which color
box is hiding a yellow square. So, for instance, if the computer
presents participants with six red boxes and four blue ones,
a smart participant would bet on the red boxes, since that’s
probably where the yellow square is hiding. Then, the computer
asks participants to bet a proportion of their points on the
correctness of their answer.
The stimulant users performed poorly on the task —
making decisions slowly and often making the wrong decision.
In addition, the longer the participants had been abusing the
drug, the worse their decision-making.
Opiate users, in comparison, showed slowed performance
but generally made the correct bet. Among the participants with
brain damage, only the ones with orbitofrontal cortex damage
showed a pattern of impaired and slowed decision-making.
In a follow-up study, the researchers depleted serotonin
levels among healthy participants and found that the
participants made poorer decisions, but their decision-making
speed was not slowed.
“This suggests that, among amphetamine users, their
poor decision-making may be associated with orbitofrontal
damage and with reduced serotonin function in that region, as
methamphetamine addicts have been shown to have reduced
signs of serotonin function in the orbitofrontal cortex post
mortem,” said Robbins.
In addition to poor decision-making, stimulant drug use
seems to make people less able to adapt when the rules of a
game change, according to a study published by Robbins and
his colleagues in Nature (Vol. 380, No. 6,569). In a procedure