As PPI infers interregional correlations and does not yield information regarding causal or directional relationships between functional coupled regions, or even whether other, unmeasured regions are driving the relationship, interpretation of our results are limited in that regard. The lack of connectivity results from the right NAcc seed may be in part explained by previous work showing left lateralized dopaminergic transmission in basal ganglia structures in response to monetary reward (Zald et al., 2004); this merits further investigation. In addition, as the orbitofrontal cortex and anterior cingulate are areas frequently implicated in processes associated with addiction (Goldstein and Volkow, 2002), it was interesting that we did not find task-related connectivity changes with these executive/cognitive areas as initially hypothesized. Additional study is needed to understand how network interactions might differ by gender, or be impacted by maturation and substance use.
