http://www.sciencedaily.com/releases/2007/...71107160233.htm

'New measurements of brain activity in individuals addicted to cocaine confirm that addicted individuals have compromised sensitivity to monetary rewards.

"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," said Rita Goldstein, who runs the neuropsychoimaging lab at the U.S. Department of Energy's Brookhaven National Laboratory where the work was done. Muhammad A. Parvaz, a Stony Brook University graduate student working with Goldstein, presented the findings at the Society for Neuroscience annual meeting in San Diego on November 7, 2007.

The researchers studied 18 current cocaine users and 18 age-matched control subjects. They outfitted each subject with a cap of electrodes to measure brain activity after instructing the subjects to press or not press a button in response to certain visual prompts. During the task, subjects were told they could earn various amounts of money for fast and accurate performance.'