Cannabis: Heavy Use Associated with Working Memory Deficits Interview with:
Dr. Matthew J. Smith PhD
Department of Psychiatry and Behavioral Sciences, Northwestern University Feinberg School of Medicine, 710 N. Lake Shore Drive, 13th Floor, Abbott Hall, Chicago, IL 60611 What are the main findings of the study?

Dr. Smith: We observed that the shapes of brain structures involved in a working memory brain circuit seemed to collapse inward in a similar fashion among both of the groups that had a history of daily cannabis use. These cannabis-related changes in shape were directly related to the participants’ poor performance on working memory tasks. Some of the shape abnormalities were more severe in the group with schizophrenia and the history of daily cannabis use. We also found that participants with an earlier age of daily cannabis use had more abnormal brain shapes. Were any of the findings unexpected?

Dr. Smith: We didn’t expect that the cannabis-related shape would be correlated with the age of onset of daily cannabis use. This finding suggests that the younger someone was when they started using daily, the more abnormal the shape of the brain structures. Although this finding is not direct evidence of causation, it appears to be consistent with a causal hypothesis. What should clinicians and patients take away from your report?

Dr. Smith: Among adolescence, working memory is a significant predictor of academic achievement. Hence, heavy cannabis use during adolescence may have negative implications for working memory, and in turn, academic achievement.

Among individuals with schizophrenia, working memory is a significant contributor to community-based functioning (e.g., social functioning, completing everyday living activities). Hence, the evidence from this study suggests that long-term cannabis use may have negative implications for working memory, and in turn, community-based functioning.

Additional research would be needed to examine whether heavy cannabis use directly or indirectly impacts academic achievement among adolescents or community-based functioning among individuals with schizophrenia. What recommendations do you have for future research as a result of this study?

Dr. Smith: Based on the cross-sectional nature of this study, the observed brain abnormalities could have predated the onset of cannabis use. Hence, the observed abnormalities could represent a biological vulnerability to substance misuse. Future research is needed to evaluate whether cannabis use contributes to brain changes over time.


 Cannabis-Related Working Memory Deficits and Associated Subcortical Morphological Differences in Healthy Individuals and Schizophrenia Subjects Schizophr Bull sbt176 first published online December 15, 2013 doi:10.1093/schbul/sbt176

Last Updated on December 16, 2013 by Marie Benz MD FAAD