A new study funded by NIDA has used brain-imaging technology to show that during a decision game, chronic marijuana users show less activity in an error-processing part of their brains than peers who do not use marijuana. These results provide preliminary evidence in the debate on whether substance abusers willfully ignore their problem or whether cognitive deficits prevent them from fully understanding their addiction and its potential consequences. Functional magnetic resonance imaging (fMRI) of 16 heavy marijuana users and 16 non-drug-using peers provided real-time pictures of brain activity during the decision game. The marijuana abusers in the study did not make more mistakes during the game than participants who did not use the drug, but they were significantly less likely to recognize that they had made the mistakes. Non-marijuana-using participants were aware of 91 percent of their mistakes during the game, and marijuana abusers were aware of only 77 percent of their mistakes. fMRI revealed that when they made errors that they did not consciously recognize, the marijuana abusers showed less activity than the other participants in an area of the brain called the anterior cingulate cortex (ACC). The authors caution that marijuana withdrawal may have played some role in the lack of error awareness, as higher scores in several categories on a marijuana craving questionnaire were associated with poorer error awareness. However, if drug abusers cannot monitor their behavior accurately, this deficit in awareness may contribute to their continued use of a drug despite the consequences or to their continued associations with situations that make them liable to relapse.

Hester R, Nestor L, Garavan H. Impaired Error Awareness and Anterior Cingulate Cortex Hypoactivity in Chronic Cannabis Users. Neuropsychopharmacology. 2009 Jun 24. [Epub ahead of print]

Source: NIDA Addiction Research News December 11, 2009
http://www.drugabuse.gov/newsroom/09/NS-12.html