Rats that are genetically predisposed to being impulsive also are more likely to become addicted to cocaine, leading researchers to conclude that addiction may have a biological basis in some cases.

The Guardian reported March 2 that the researchers said that the findings point to a "hidden vulnerability" that the impulsive rats had for addiction. The study involved a test where rats were given a food reward when a light was shined; most rats waited for the light, but a few could not resist the urge to run to the food place before the light came on. Further studies showed that these impulsive rats were more likely to become addicted than the other rats, and had fewer dopamine receptors in the nuclear accubens region of their brains.

"Being impulsive to begin with seems to be an important vulnerability trait marker that predisposes to excessive cocaine taking," said researcher Jeffrey Dalley of Cambridge University. "There are several studies now showing [dopamine] receptors to be a natural 'brake' in the brain that regulates the amount of drug intake; too few and intake seems to increase ... this is the first study to link such changes with impulsivity."

"We have known for a long time that some behaviors are associated with drug addiction -- such as impulsivity and risk taking in general," added Gerome Breen, an addiction researcher at the Institute of Psychiatry at King's College London. "What this study does is identify a biological basis for the behavior and the mechanism by which it leads to addiction." Breen was not involved in the study.

The research was published in the March 2007 issue of the journal Science.