NIDA-supported researchers from Brookhaven National Laboratory and the State University of New York at Stony Brook have found evidence in humans that dopamine plays a role in the conditioned cue response to food. Cues—seeing, smelling, and tasting something enjoyable—increase the desire for the reward without necessarily enhancing the pleasure of the reward itself.

Positron emission tomography (PET) was used to measure changes in dopamine in the brains of 10 healthy adults (eight men and two women) during food and neutral stimulations. Food stimulation consisted of the participants viewing, smelling, and tasting their favorite foods but not actually eating the foods. For neutral stimulation, participants described their family genealogy in detail. Prior to and during food stimulation, participants were instructed to rate their feelings of "hunger," "desire for food," "alertness," "stimulation," and "talkativeness" on a scale of 1 to 10. Participants had fasted 16-20 hours before PET scans were conducted.

Food stimulation caused an increase in dopamine in the dorsal striatum but not in the ventral striatum,

where the nucleus accumbens is located. This suggests that dopamine may be involved in food motivation that is distinct from its role in regulating food's reward effects through the nucleus accumbens. Previous research has linked increases in dopamine in the nucleus accumbens, the reward center of the brain, with addiction.

What it means: The finding that dopamine may play a role in cue-induced effects could have important implications in drug addiction research. Many individuals addicted to drugs, especially cocaine and nicotine, are susceptible to cue-induced cravings. A better understanding of the biological basis of cue-related behaviorsmay provide better insights in the development of more effective behavioral and pharmacological treatments for drug addiction.

The study was published by lead investigator Dr. Nora Volkow in the electronic online journal, Synapse, and is due to be published in the June 1, 2002 hard-copy issue of Synapse.

NIDA NewsScan, May 28, 2002

Craving for cocaine––an often irresistible urge that can be triggered by environmental cues linked to past drug use (being with certain people or in a certain location)––is associated with the same brain circuits that are involved in response to other, nondrug stimuli.

Scientists at the Medical College of Wisconsin in Milwaukee showed4-minute films depicting drug use, nature scenes, or explicit sexual activity to cocaine users and to participants with no history of cocaine use.

In particular, both users and non-users reported similar levels of arousal while watching the sex film, and functional magnetic resonance imaging (fMRI) revealed similar patterns of regional brain activation in both groups. Most regions identified as cocaine craving sites were similarly activated by sexual stimuli, indicating that common circuits are involved in drug and nondrug responses.

Lead investigator Dr. Elliot Stein notes that in response to the sexfilm, drug users showed less

activation in these sites than did the non-users. This suggests that cocaine craving not only acts on the brain’sreward circuits, it actually co-opts them, changing the user’s normal emotionally driven preferences. According to Dr. Stein, this may have serious consequences for decision-making by cocaine users. There were no differences between users and non-users when they viewed the nature film.

What it means: The brain sites involved in cocaine craving are associated with emotional response, information processing, and working memory. What is already known about normal learning, memory, and emotions may be applied to cue-induced craving and the development of appropriate pharmacological, behavioral, and cognitive therapies.

Dr. Stein and his colleagues describe their research in the November issue of the American Journal of Psychiatry.

NIDA NewsScan, December, 2000