The brain may have different circuits for handling the perceived rewards from drugs as opposed to healthier passions, such as food, suggesting new potential strategies for the treatment of addiction.

In the novel A Clockwork Orange, a medical treatment designed to prevent an ultra-violent teenager from committing acts of aggression unexpectedly renders him incapable of listening to classical music. Though a fictional example, this highlights a serious concern inherent in developing therapies for psychiatric disorders—keeping a treatment focused and minimizing unexpected side effects. A new study from Nature Neuroscience (April) offers potentially important new findings in this area, revealing that it may be possible to therapeutically diminish the 'reward' associated with addictive drugs without affecting reward signals resulting from other stimuli.

Previous studies have shown that a brain structure called the subthalamic nucleus (STN) is involved in processing reward pathway signaling in response to certain stimuli—including drugs of addiction. In an effort to examine more closely the role of this brain region, Christelle Baunez of the Université de Provence (Marseilles, France) and her colleagues chemically induced STN lesions in rats, then observed the impact of these lesions on the animals' behavior in a variety of studies designed to measure the effort that rats would devote to obtaining food pellets or cocaine.

In experiments in which a single press of a bar yielded a food or cocaine reward, both the experimental and control rats behaved similarly. However, when the study was changed so that each reward event required an increased amount of effort (i.e., more than one press of the bar), it became clear that control rats were willing to put in significantly more effort to obtain cocaine rewards. Conversely, in those same studies, the experimental rats proved more willing to work hard toward a food reward.

Follow-up studies measuring 'place-conditioning'—the amount of time that an animal spends in an environment associated with a specific reward—mirrored these findings, showing that rats with STN lesions showed a reduced tendency to linger in a cocaine-associated compartment relative to controls without lesions. The opposite was true for food-associated environments, for which the rats with STN lesions showed an enhanced preference.

These findings not only seem to be consistent with previous findings linking drug addiction with STN dysfunction, but also suggest the potential for more focused strategies for treating addiction. “These findings have important functional implications,” the authors indicate, “as they suggest that different parallel microcircuits mediate responses for natural reward versus cocaine... this possibility opens new perspectives for the development of specific and efficient treatments for drug abuse.”