longitudinal studies of abstinent polysubstance users: If our speculation/interpretation were correct, the observed GM differences – and particularly the larger WM volumes – should diminish with duration of abstinence as the substance withdrawal-related inflammation subsides over time. Such a dynamic change has been suggested in abstinent methamphetamine users (Chang et al., 2007). Methodological issues in studying brain effects of polysubstance dependence with relevance to the above discussion were recently reviewed (Mackey and Paulus, 2013).
