The study, published in the Journal of Neuroscience, compared brain activity -- traced by functional magnetic resonance imaging -- in nine people who were recovering alcoholics in abstinence and 10 people with no history of substance abuse when faced with a choice between less money "now" or more money "later."

Senior study author Dr. Howard Fields of the University of California, San Francisco Ernest Gallo Clinic and Research Center said that sober alcoholics chose the "now" reward almost three times more often than the control group, the study said. The imaging revealed reduced activity in the orbital frontal cortex in the brains of subjects who preferred now.

The researchers also looked at a gene mutation associated with lower dopamine levels and found people with two copies of this allele -- resulting in the lowest dopamine levels -- had significantly higher frontal and parietal activity also chose "now over later" significantly more often.

"The genetic findings raise the hopeful possibility that treatments aimed at raising dopamine levels could be effective treatments for some individuals with addictive disorders," Fields said in a statement.