In Reply Van Holst et al provide a thoughtful comment on our meta-analysis of functional magnetic resonance imaging studies investigating reward processing in addiction.1 Their letter mainly focuses on 2 methodological points.
First, van Holst et al highlight that the tasks used in gambling disorder (GD) studies are less homogeneous than those in substance use disorder (SUD) studies. Although this is correct—and reflects fewer studies available on GD—we believe that contrast homogeneity, rather than task homogeneity, is what primarily matters. In keeping with this, we carefully selected those contrasts that capture the 2 cognitive processes of interest in our meta-analysis, namely monetary reward anticipation and outcome. Incidentally, this is the reason why some of these contrasts depart from those reported in the original articles. It is worth emphasizing that heterogeneity is a pervasive problem in (neuroimaging) meta-analyses that extends beyond tasks and includes heterogeneity in design efficiency, data analysis, and population selection. However, task heterogeneity is not necessarily detrimental, as the convergence of activations despite such heterogeneity ensures that the results are not due to idiosyncrasies in task design and are generalizable across a variety of paradigms.2
Schellekens AF, Luijten M, Sescousse G. Are There Differences in Disruptions of Reward Processing Between Substance Use Disorder and Gambling Disorder?—Reply. JAMA Psychiatry. 2017;74(7):760–761. doi:10.1001/jamapsychiatry.2017.1054
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