The monetary gambling task (MGT) used in this study is illustrated in Fig 1. Each trial began with a choice stimulus (CS), with two numbers 10¢ (left box) and 50¢ (right box) displayed for 800 ms. The participants selected a bet of either 50¢ or 10¢, and received feedback of either loss or gain for the selected amount (outcome stimulus, OS). The task details have been described in our previous publications [14,25,41,49]. The inter-stimulus interval (ISI) between a CS and OS, and between an OS and next CS is 1500 ms. The task involved a total of 172 trials, each with one of four possible outcomes: Loss 50¢, Loss 10¢, Gain 50¢, and Gain 10¢. Irrespective of the overall amounts chosen during the task, the probability of loss and gain outcomes were 50% (i.e., the number of ‘red’ and ‘green’ outcomes were equal), although the participants were not aware of this information. However, since the subject has the option to freely select the amount during each trial, the relative probability for each of the four outcomes (+50, −50, +10, −10)
