The fMRI paradigm was a slow event-related card-guessing game [29] that allows examination of response to monetary reward and reliably engages the striatum (see Figure 1). Participants received win, loss, or a neutral control feedback for each trial. Participants were told that their performance would determine a post-scan monetary reward, with $1 for each win and 50 cents deducted for each loss with no money being gained or deducted for the control blocks. The 45 trials were divided into three different block types: win, loss, and control. These blocks were presented in fixed, pseudorandom order with predetermined outcomes that were identical across participants. During each win and loss trial, participants guessed via button press whether the value of a hidden number was high or low (3 s); learned the value of the hidden number (.5 s); and received outcome feedback (.5 s). Feedback consisted of a green upward-facing arrow for a win outcome and a red downward-facing arrow for a loss outcome. A crosshair was then presented for 3 s (intertrial interval), for a total trial length of 7 s.
