Nov. 12 (HealthDay News) -- Cocaine addiction dulls the brain's sensitivity to even monetary rewards, U.S. researchers report.

A team at the U.S. Department of Energy's Brookhaven National Laboratory analyzed brain activity in 18 cocaine addicts and 18 age-matched healthy people.

The participants were outfitted with a cap of electrodes that measured brain activity as they pressed or didn't press buttons in response to visual prompts. During this task, the participants were told they could earn various amounts of money for fast and accurate performance.

The results showed that the cocaine addicts had a blunted brain response to the offer of a monetary reward.

The findings were presented Nov. 7 at the Society for Neuroscience annual meeting in San Diego.

"This altered sensitivity to reward may help explain why some drug-addicted individuals are unable to modify their drug-taking behavior, even in the face of well-understood negative consequences and/or positive incentives for behavioral change," Rita Goldstein, who runs the neuropsychoimaging lab at Brookhaven, said in a prepared statement.

In previous studies using functional magnetic resonance imaging, researchers in Goldstein's lab found similar compromised brain sensitivity to monetary reward in cocaine addicts.

"Individuals with such blunted neural and behavioral sensitivity to rewards may have a particularly difficult time responding to abstract incentives designed to motivate behavioral changes -- especially when outside of a structured treatment environment or when rewards are not readily available or clearly contingent on behavior," Goldstein said.

SOURCE: Brookhaven National Laboratory, news release, Nov. 7, 2007