Fig. 1.

During fMRI scanning participants performed a gambling task with the intent to win as many points as possible. A fixation cross was presented for 0.5 s followed by the numbers ‘5’ and ‘25’ (choice cue). The left/right position of these cues was randomized. Participants chose a number by pressing the corresponding button. One second later, the boxes around the numbers turned both green (indicating gain) and both red (indicating loss) and stayed on the screen for 1.5 s. The intertrial interval was 3 s plus RT. When participants chose ‘5’, they could gain or lose 5 (80% of trials, expected small gain or loss), 7 (10%, unexpected small gain or loss) or 125 points (10%, unexpected large gain or loss); when they chose ‘25’, they could win or lose 25 (80%, expected small gain or loss), 27 (10%, unexpected small gain or loss), or 125 points (10%, unexpected large gain or loss). In the present example, the participant chose ‘5’, and gained 125 points. The color bar below indicated the total amount of points collected so far.