Scientists have shed new light on dopamine's role in the brain's reward system.
The findings could provide insight into impulse control problems associated with addiction and a number of psychiatric disorders.
A joint study by the University of Michigan and University of Washington found that, contrary to the prevailing conception, differences in individuals' styles of response to environmental cues can fundamentally influence chemical reward patterns in the brain.
Deeper understanding of these differences between individuals may lead to new preventive tools or treatments for compulsive behavior.
The researchers studied rats that had been selectively bred for certain behavioral traits, including different proclivities for addictive drugs. Rats in the drug-prone group tended to focus their attention on the lever. The other group cared a lot more about the place where the food actually appeared.
Still, if the rats' brains saw the lever merely as a signal that accurately predicted the arrival of the food, the dopamine reward for both groups should be the same.
However, if the dopamine reward was tied to the strength of the rats' desire for lever itself, one would expect a different pattern for each of the two groups.
U-M's collaborators at the University of Washington used a technique called fast-scan cyclic voltammetry to measure the dopamine responses in the rats' brains as they shifted over mere fractions of a second.
Their analysis showed that the drug-prone rats got a jolt of happiness just from the lever, while the food-oriented rats did not.
And their desire for the lever continued, even when the food reward was removed.
The findings were published online today in the journal Nature ahead of print publication.