Reduced Sensitivity to Immediate Reward during Decision-Making in Older than Younger Adults

Abstract

We examined whether older adults differ from younger adults in the degree to which they favor immediate over delayed rewards during decision-making. To examine the neural correlates of age-related differences in delay discounting we acquired functional MR images while participants made decisions between smaller but sooner and larger but later monetary rewards. The behavioral results show age-related reductions in delay discounting. Less impulsive decision-making in older adults was associated with lower ventral striatal activations to immediate reward. Furthermore, older adults showed an overall higher percentage of delayed choices and reduced activity in the dorsal striatum than younger adults. This points to a reduced reward sensitivity of the dorsal striatum in older adults. Taken together, our findings indicate that less impulsive decision-making in older adults is due to a reduced sensitivity of striatal areas to reward. These age-related changes in reward sensitivity may result from transformations in dopaminergic neuromodulation with age.

Reduced Striatal Responses to Reward Prediction Errors in Older Compared with Younger Adults

“…1). Consistent with previous findings, we expected that older adults would be impaired in learning from reward (Eppinger and Kray, 2011;Eppinger et al, 2011). Based on the literature in younger adults, we predicted that activity in dopaminergically innervated areas such as the vStr and ventromedial PFC should be correlated with reward prediction error (Pessiglione et al, 2006;Klein et al, 2007;Jocham et al, 2011;Niv et al, 2012).…”

“…Participants also performed a delay-discounting experiment in the scanner. These data are reported in Eppinger et al, (2012).…”

“…As in previous studies, we used an adaptive response deadline procedure in which we adjusted the response deadlines (700 -1300 ms) depending on the number of time-out trials Eppinger and Kray, 2011). Mean response deadlines were 1071 ms (SD ϭ 211 ms) for younger adults and 1139 ms (SD ϭ 194) for older adults.…”

Altered behavioral and neural responsiveness to counterfactual gains in the elderly

“…Task-related activity in the fronto-striatal circuit was also affected by age, where older adults generally showed stronger responses to factual and counterfactual consequences in the striatum, but a non-significant correlation with reward predictions in the vmPFC. Our findings are in general agreement with previous literature showing that relatively poor decision making in multialternative choice tasks in older adults is related to aberrant reward prediction and prediction error processing in this fronto-striatal circuit (Chowdhury et al, 2013;Eppinger, Walter et al, 2013;Eppinger, Nystrom, et al, 2012;Eppinger, Schuck, et al, 2013;Grady, 2012;Hedden & Gabrieli, 2004;Rademacher, Saalma, Grunder, & Sprecklemeyer, 2014;SamanezLarkin et al, 2007;Samanez-Larkin et al, 2011;Samanez-Larkin et al, 2014;Samanez-Larkin & Knutson, 2015;Vink et al, 2015;), and extends these findings to include altered processing of counterfactual consequences. Finally, this study advocates the modelbased fMRI experimental design to study both behavioral and neural systems for decision making between age groups but cautions that model fits be carefully taken into account when drawing conclusions about group differences.…”

“…The FPEQ model explained the data from both age groups better than three other models previously used in the literature, which shows that decision making guided by reward predictions, rather than outcome-response strategies, such as win-stay-lose-shift, was the best fit for the elderly. The reward predictions, prediction errors and FPEs from the FPEQ model, were correlated with neural activity in the fronto-striatal circuit previously implicated in agerelated differences in processing reward predictions and reward prediction errors (Chowdhury et al, 2013;Eppinger et al, 2012;Rademacher et al, 2014;Samanez-Larkin et al, 2007Vink et al, 2015). Importantly, age did not significantly affect TD learning rate nor the average experienced TD error.…”