It is of note that another WM intervention study using PET and the Klingberg et al. (2002) training package showed changes in cortical D1 receptors post training, but failed to demonstrate effects on the striatal D2 system (McNab et al., 2009). Regarding the discrepancy in findings between studies, in McNab et al. DA binding was assessed at rest only and the training program employed promoted sustained maintenance processes. As noted, extrastriatal D1 receptors seem to be particularly critical to maintenance of information in WM, whereas striatal D2 receptors are more critical to transient processes such as updating (Bilder et al., 2004; Cools and D’Esposito, 2011; Durstewitz and Seamans, 2008). These differences may account for the differential patterns observed with regard to the effects of WM training on DA binding, a key point being that also the DA D2 system seems to be modifiable by training.