Research: Act on impulse

Can impulsivity predict individuals vulnerable to drug use?

The link between stimulant addiction and impulsivity is well known, but does impulsivity lead to drug use, or is it a consequence of this behaviour? To try and answer this question, a team from the Behavioural and Clinical Neuroscience Institute at the University of Cambridge, led by Jeff Dalley, looked at cocaine self-administration in rats.

The team used a test called the 5-CSRTT (five-choice serial reaction time task) to identify naturally impulsive rats. In this test, rats receive a food reward if they wait for a light to illuminate in one of five holes before moving.

Researchers found that a small percentage of the rats consistently acted impulsively, moving before any light showed. These animals were more likely than nonimpulsive rats to go on and self-administer cocaine.

The dopamine system, part of the brain's reward pathways, is known to be important in drug addiction. In particular, low levels of D2/3 dopamine receptors have been linked to chronic drug exposure in humans. The Cambridge research team found that impulsive rats had fewer D2/3 dopamine receptors, even before exposure to cocaine – suggesting that dopamine dysfunction may be a cause of vulnerability to addiction, not a consequence of drug taking.

The researchers suggest that low D2/3 dopamine receptor levels may not just make some people more likely to try cocaine, because of greater impulsivity, but may actually encourage compulsive drug-taking habits.

• This research was funded by the Wellcome Trust and the Medical Research Council.

External links

• Dalley JW et al. Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement. Science 2007;315(5816):1267–70.