Modulation of Caudate Activity

studies have not examined the extent to which the dorsal 3 Department of Psychology and ventral striatum are activated in response to dis-New York University plays indicating monetary rewards and punishments New York, New York 10003 presented unpredictably in time. However, there is evidence that randomly presented primary rewards elicit striatal activation. Electrophysiological recording stud-Summary ies in monkeys have shown that unpredicted primary rewards cause activity of dopaminergic neurons in the Research has increasingly implicated the striatum in substantia nigra and ventral tegmental area (Schultz et the processing of reward-related information in both al., 1997), and these neurons project to dorsal and ven-animals and humans. However, it is unclear whether tral striatum, respectively (Haber and Fudge, 1997). In human striatal activation is driven solely by the he-addition, an fMRI study using human subjects found an donic properties of rewards or whether such activation enhancement of activity in the ventral striatum when is reliant on other factors, such as anticipation of up-primary liquid rewards were presented in an unpredict-coming reward or performance of an action to earn a able, rather than a predictable, manner (Berns et al., reward. We used event-related functional magnetic 2001). Activity in dorsal striatum, however, was not re-resonance imaging to investigate hemodynamic reported in this experiment. sponses to monetary rewards and punishments in To understand how the striatum reacts to unpredict-three experiments that made use of an oddball para-able rewards and punishments, we used an oddball par-digm. We presented reward and punishment displays adigm in which a meaningless standard habituating randomly in time, following an anticipatory cue, or stimulus (a purple square) was repeatedly presented, following a button press response. Robust and differ-interrupted with infrequent oddball stimuli indicating ential activation of the caudate nucleus occurred only monetary gain or loss (Figure 1). This design allowed us when a perception of contingency existed between the to present reward and punishment displays at varying button press response and the outcome. This finding intervals. Oddball paradigms have been used exten-suggests that the caudate is involved in reinforcement sively in ERP experiments (Courchesne et al., 1975; of action potentially leading to reward, rather than in Johnson, 1986; Sutton et al., 1965) and more recently processing reward per se. Introduction this type of paradigm, the repeating standard stimulus presentations serve as a baseline, against which activity The subjective experience of receiving a reward or pun-elicited by the oddballs can be compared. ishment …