Every day, humans make countless decisions that require the integration of information about potential benefits (i.e. rewards) with other decision features (i.e. effort required, probability of an outcome or time delays). Here, we examine the overlap and dissociation of behavioral preferences and neural representations of subjective value in the context of three different decision features (physical effort, probability and time delays) in a healthy adult life span sample. While undergoing functional neuroimaging, participants (N = 75) made incentive compatible choices between a smaller monetary reward with lower physical effort, higher probability, or a shorter time delay versus a larger monetary reward with higher physical effort, lower probability, or a longer time delay. Behavioral preferences were estimated from observed choices, and subjective values were computed using individual hyperbolic discount functions. We found that discount rates were uncorrelated across tasks. Despite this apparent behavioral dissociation between preferences, we found overlapping subjective value-related activity in the medial prefrontal cortex across all three tasks. We found no consistent evidence for age differences in either preferences or the neural representations of subjective value across adulthood. These results suggest that while the tolerance of decision features is behaviorally dissociable, subjective value signals share a common representation across adulthood.

Although research on aging and decision making continues to grow, the majority of studies examine decisions made to maximize monetary earnings or points. It is not clear whether these results generalize to other types of rewards. To investigate this, we examined adult age differences in ninety-two healthy participants aged 22–83. Participants completed nine hypothetical discounting tasks, which included three types of discounting factors (time, probability, effort) across three reward domains (monetary, social, health). Participants made choices between a smaller magnitude reward with a shorter time delay / higher probability / lower level of physical effort required and a larger magnitude reward with a longer time delay / lower probability / higher level of physical effort required. Older compared to younger individuals were more likely to choose options that involved shorter time delays or higher probabilities of experiencing an interaction with a close social partner or receiving health benefits from a hypothetical drug. These findings suggest that older adults may be more motivated than young adults to obtain social and health rewards immediately and with certainty.

The relatively modest spatial resolution of positron emission tomography (PET) increases the likelihood of partial volume effects such that binding potential (BP) may be underestimated. Given structural grey matter losses across adulthood, partial volume effects may be even more problematic in older age leading to overestimation of adult age differences. Here we examined the effects of partial volume correction (PVC) in two studies from different sites using different high-affinity D2-like radioligands (18 F-Fallypride, 11C-FLB457) and different PET camera resolutions (∼5 mm, 2.5 mm). Results across both data sets revealed that PVC increased estimated BP and reduced, though did not eliminate, age effects on BP. As expected, the effects of PVC were smaller in higher compared to lower resolution data. Analyses using uncorrected data that controlled for grey matter volume in each region of interest approximated PVC corrected data for some but not all regions. Overall, the findings suggest that PVC increases estimated BP in general and reduces adult age differences especially when using lower resolution cameras. The findings suggest that the past 30 years of research on dopamine receptor availability, for which very few studies use PVC, may overestimate effects of aging on dopamine receptor availability.

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