Differential activation of the striatum for decision making and outcomes in a monetary task with gain and loss

We examined brain activation for decision making and for different monetary outcomes in a two-alternative choice task with monetary rewards and punishments. Brain hemodynamic changes were monitored by functional MRI (fMRI) when seventeen healthy volunteers performed a task in which they were required to press one of two buttons (button 1 or 2) which increased or decreased their previously endowed money depending upon accord or disaccord with the number (1 or 2) which was displayed later. The amount of money subjects gained or lost was large when they selected 2 and small when they selected 1. They were informed in advance that the order of the appearance of 1 or 2 at outcome phase was predetermined and random, irrespective of their selection, and that the expected value was mathematically zero for both selecting 1 and 2. Results of fMRI showed that bilateral putamen and nucleus accumbens were more activated when selecting large gain or loss option than selecting small gain or loss option, and the right putamen and nucleus accumbens were more activated for gain outcome than for loss outcome. No significantly different activation of the striatum was found between large gain outcome and small gain outcome, suggesting that activity of the striatum at outcome phase was insensitive for reward magnitude when expectation by subject was already performed. We also found that activations of the bilateral putamen were correlated parametrically with stock amount of money.