To further investigate the overlap and distinctiveness of the neural networks related to reward-dependent and reward-independent recruitment of neural processing resources Krebs et al. (2012) systematically crossed reward and attentional demand prediction in a subsequent fMRI study. Both factors activated selective but also similar neural networks with mostly additive effects, but also interactions for some areas, including the dopaminergic midbrain, with maximal activity in response to cues that predicted difficult potential-reward trials. These findings were taken to support the view that the dopaminergic midbrain plays a role in a broader network that is involved in the control of neuro-cognitive processing resources to optimize behavior when it is particularly worthwhile. Importantly, the above task required attentional orienting and task preparation immediately in response to the cue, which sets it apart from typical neuroeconomic experiments that emphasize evaluative processes and have conceptualized task demands as costs that get discounted from the possible reward (Croxson et al., 2009; McGuire and Botvinick, 2010). There are however important questions that cannot be addressed with fMRI because of the slow characteristics of the hemodynamic response. Most
