Working memory subsystems are impaired in chronic drug dependents.

Background: A large body of research that has investigated substance dependence and working memory (WM) resources, yet no prior study has used a comprehensive test battery to examine the impact of chronic drug dependence on WM as a multi-component system.

Objectives: This study examined the efficiency of several WM components in participants who were chronic drug dependents. In addition, the functioning of the four WM components was compared among dependents of various types of drugs.

Method: In total, 128 chronic drug dependents participated in this study. Their average age was 38.48 years, and they were classified into four drug-dependence groups. Chronic drug dependents were compared with a 36-participant control group that had a mean age of 37.6 years. A WM test battery that comprised eight tests and that assessed each of four WM components was administered to each participant.

Results: Compared with the control group, all four groups of drug dependents had significantly poorer test performance on all of the WM tasks. Among the four groups of drug users, the polydrug group had the poorest performance scores on each of the eight tasks, and the performance scores of the marijuana group were the least affected. Finally, the forward digit span task and the logical memory tasks were less sensitive than other tasks when differentiating between marijuana users and the normal participants.

Conclusion: The four components of WM are impaired among chronic drug dependents. These results have implications for the development of tools, classification methods and therapeutic strategies for drug dependents.