Wait for the Second Marshmallow? Future-Oriented Thinking and Delayed Reward Discounting in the Brain

Our brains are equipped with the ability to mentally project us to the future so that we can explore potential actions and outcomes in advance. As Karl Popper famously said, we should ‘‘.let our false theories die in our stead’’ (Popper, 1963). Future-oriented thinking is indeed a basic operation of our proactive brain (Bar et al., 2007), and mental simulation serves the basis for many cognitive processes (e.g., Bar, 2009; Barsalou, 2009; Hassabis and Maguire, 2009; Buckner and Carroll, 2007; Moulton and Kosslyn, 2009; Schacter and Addis, 2009). One domain where future-oriented simulations could be particularly beneficial is in assessing the value of future rewards. In a famous experiment from the late 1960s, Walter Mischel and colleagues asked four-year-old children to choose between one marshmallow immediately or, if they could wait, two marshmallows twenty minutes later (see an illuminating popular coverage in Lehrer, 2009). The vast majority of the children opted for the immediate gratification of a single marshmallow. These experiments are traditionally taken as studies of selfcontrol and impulsivity, and the dominant neural explanation to this impulsive decision making in children focuses on their yet immature prefrontal cortex. How exactly does the prefrontal cortex regulate impulsive behavior? The ingenious paper by Peters and Büchel (2010) in this issue of Neuron provides a convincing account. They studied the mechanisms required for an accurate evaluation of future rewards using the phenomenon