Academic journal article Cognitive, Affective and Behavioral Neuroscience

Adult Age Differences in Frontostriatal Representation of Prediction Error but Not Reward Outcome

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Adult Age Differences in Frontostriatal Representation of Prediction Error but Not Reward Outcome

Article excerpt

Published online: 23 May 2014

© The Author(s) 2014. This article is published with open access at Springerlink.com

Abstract Emerging evidence from decision neuroscience suggests that although younger and older adults show similar frontostriatal representations of reward magnitude, older adults often show deficits in feedback-driven reinforcement learning. In the present study, healthy adults completed reward-based tasks that did or did not depend on probabilistic learning, while undergoing functional neuroimaging. We observed reductions in the frontostriatal representation of prediction errors during probabilistic learning in older adults. In contrast, we found evidence for stability across adulthood in the representation of reward outcome in a task that did not require learning. Together, the results identify changes across adulthood in the dynamic coding of relational representations of feedback, in spite of preserved reward sensitivity in old age. Overall, the results suggest that the neural representation of prediction error, but not reward outcome, is reduced in old age. These findings reveal a potential dissociation between cognition and motivation with age and identify a potential mechanism for explaining changes in learning-dependent decision making in old adulthood.

Keywords Aging . Reward . Motivation . Learning . Decision making . Medial prefrontal cortex . Ventral striatum

Adult development and aging has been associated with relative stability in some aspects of motivational function but with decreases in some aspects of cognitive function (Carstensen, 2006;Grady,2008; Reuter-Lorenz & Lustig, 2005;Samanez-Larkin & Carstensen, 2011; Samson & Barnes, 2013). Until recently, the majority of studies into the cognitive neuroscience of aging have examined separately either motivational or cognitive function. However, an emerging literature on age differences in reward learning and decision making has facilitated the examination of potential overlap or dissociation in these processes. The initial set of neuroimaging findings from this literature attributed deficits in reward learning in older age to structural and functional differences in frontostriatal circuitry (Eppinger, Hämmerer, & Li, 2011; Hämmerer & Eppinger, 2012; Samanez-Larkin & Knutson, 2014). Although older adults show intact, or even enhanced, frontostriatal responses to reward outcomes (Cox, Aizenstein, & Fiez, 2008; Samanez-Larkin et al., 2007;Schottetal.,2007), they also show decreased ventral striatal function in time-limited learning tasks (Chowdhury et al., 2013; Eppinger, Schuck, Nystrom, & Cohen, 2013;Melletal.,2009; Samanez-Larkin, Kuhnen, Yoo, & Knutson, 2010). Some have suggested that adult age differences in reward-based decision making are due to a motivational deficit, such that older adults are less sensitive to reward than are younger adults (Eppinger, Nystrom, & Cohen, 2012). However, an alternative account of these collected findings may be that, whereas sensitivity to reward and previously learned reward associations remain intact over the adult lifespan, a network of neural systems that supports novel reward learning changes with age. This view suggests a potential dissociation between motivation and cognition in the aging brain.

Accordingly, a recent review of behavioral research showed the largest and most reliable adult age differences in decision tasks that depend on learning novel stimulus-reward associations, but few age differences in tasks that did not require recent learning (Mata, Josef, Samanez-Larkin, & Hertwig, 2011). Building on these findings, a diffusion tensor-imaging study revealed that the structural connectivity of the prefrontal cortex to the striatum could account for age differences in probabilistic reward learning (Samanez-Larkin, Levens, Perry, Dougherty, & Knutson, 2012). Together, this prior evidence has suggested that although older adults show intact sensitivity to reward magnitude (Samanez-Larkin et al. …

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