Risk, Reward, and Decision-Making in a Rodent Model of Cognitive Aging

Abstract

Impaired decision-making in aging can directly impact factors (financial security, health care) that are critical to maintaining quality of life and independence at advanced ages. Naturalistic rodent models mimic human aging in other cognitive domains, and afford the opportunity to parse the effects of age on discrete aspects of decision-making in a manner relatively uncontaminated by experiential factors. Young adult (5–7 months) and aged (23–25 months) male F344 rats were trained on a probability discounting task in which they made discrete-trial choices between a small certain reward (one food pellet) and a large but uncertain reward (two food pellets with varying probabilities of delivery ranging from 100 to 0%). Young rats chose the large reward when it was associated with a high probability of delivery and shifted to the small but certain reward as probability of the large reward decreased. As a group, aged rats performed comparably to young, but there was significantly greater variance among aged rats. One subgroup of aged rats showed strong preference for the small certain reward. This preference was maintained under conditions in which large reward delivery was also certain, suggesting decreased sensitivity to reward magnitude. In contrast, another subgroup of aged rats showed strong preference for the large reward at low probabilities of delivery. Interestingly, this subgroup also showed elevated preference for probabilistic rewards when reward magnitudes were equalized. Previous findings using this same aged study population described strongly attenuated discounting of delayed rewards with age, together suggesting that a subgroup of aged rats may have deficits associated with accounting for reward costs (i.e., delay or probability). These deficits in cost-accounting were dissociable from the age-related differences in sensitivity to reward magnitude, suggesting that aging influences multiple, distinct mechanisms that can impact cost–benefit decision-making.

Age differences in strategy selection and risk preference during risk-based decision making.

“…While the present experiment was not explicitly designed to address the role of task design in influencing strategy selection, our results placed in the context of recent findings using different task variables (Gilbert et al, 2012), suggest that two factors are particularly important in determining whether or not multiple strategies will be engaged in a given experiment. These include the magnitude difference between reward sizes and the degree of reward uncertainty.…”

“…This strategy may have been chosen by some young rats, because the value between the overall expected reward gains from each option may not have been different enough for them. In contrast, Gilbert et al (2012) used probabilities going down to zero percent. This procedure resulted in making the choice for the uncertain reward far riskier.…”

“…While collecting the data for this study, a similar experiment to the current one was published (Gilbert et al, 2012). Thus, this manuscript builds on those results and highlights similarities and differences obtained between studies to further our understanding of decision making in aged rats.…”

A marker of biological ageing predicts adult risk preference in European starlings, Sturnus vulgaris

“…In rats, chronologically older animals performed comparably to young on average in a risky choice task, although there was greater between-individual variation in risk preference among older rats (Gilbert et al 2012). In humans, the prevailing finding has been for greater risk aversion with chronological ageing (Harbaugh et al 2002; Deakin et al 2004; Dohmen and Falk 2010; Mohr et al 2010; Boyle et al 2011; Rutledge et al 2016; although see Cavanagh et al 2012; Pachur et al 2017), a pattern similar to that in our starlings in respect of our biomarker of biological ageing.…”

“…We note however that greater developmental telomere attrition was associated with slower autoshaping performance in one of these cohorts (Nettle, Andrews, et al 2015), but also that this measure may reflect differences in neophobia rather than purely cognitive ability (Feenders and Bateson 2013). Similarly, risk preference among aged rats was not associated with performance in a spatial learning task (Gilbert et al 2012). It must in addition be emphasized that our result is essentially correlational—telomere loss, as a biomarker of biological ageing, predicted risk-taking behavior, yet the link is not necessarily causally mechanistic (for discussion of causal links between telomere dynamics and behavior, see Bateson and Nettle 2018).…”