Abstract
An fMRI task developed in our laboratory has consistently identified the head of the caudate nucleus as a region with distinct responses to positive and negative outcomes (Delgado et al., 2000, Delgado et al., 2003, Tricomi et al., 2004). Subjects are engaged in a guessing game in which they receive monetary gain for correct guesses and monetary loss for incorrect guesses. Following a rewarding outcome, the caudate exhibits a relatively sustained hemodynamic response, while punishment responses are characterized by an early, high-amplitude peak response followed by a below-baseline dip in the caudate signal. This response pattern has been replicated across multiple studies in young adults; however, no published evidence has yet established the nature of reward and punishment signals in the striatum of healthy older adults. Therefore, the purpose of the current study was to establish a valid method for measuring reward- and punishment-related activity in healthy aging, and to describe any age-related effects on the hemodynamic responses found in the striatum. Twenty older adults (51-68 y) and thirteen young adults (18-28 y) were scanned as they completed the card-guessing task. Older adults exhibited robust, outcome-specific responses in the anterior caudate with bilateral foci of activation that overlapped with the activation found in the young adults. Furthermore, older adults retained key features of the typical caudate response profile, with a sustained increase in the signal following reward outcomes and a decrease in the signal following punishments. However, older adults did not demonstrate an early, high-amplitude peak in the punishment response, which has been reported for earlier studies and was observed in the current young-adult sample. Finally, voxel-wise analyses identified two small clusters at or near the anterior caudate where older adults’ signal appeared somewhat blunted relative to that of the young adults; similar blunting effects were found in a number of other regions throughout the brain. Overall, these findings validate the use of the card-guessing paradigm to assess outcome-specific responses in the striatum of older adults, and they point to some possible age-related effects that may be worthwhile to investigate in future studies.
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