Neural correlates of age-related changes in social decisions from episodic memory

Older adults are frequent victims of financial scams. Previous behavioral research suggests that this may be due to systematic biases in how they make decisions about whom to trust: for instance, Lempert et al. (2022) found that relative to younger adults, older adults were more likely to base decisions about whether to re-engage with someone on how generous that person looked, rather than on their memory for how they had previously behaved. Here, we aimed to identify the neural correlates of these age-dependent changes in social decision-making in order to clarify the mechanism by which they emerge. Using functional Magnetic Resonance Imaging (fMRI), we measured neural activity while a total of 86 participants - 45 younger and 41 older adults - learned about how much of a $10 endowment an individual, represented by a picture of their face, was willing to share with them in a dictator game. After this encoding phase, participants then made decisions about whom they wanted to play another round of the dictator game with. In line with previous findings, we found that older adults did not reliably prefer to re-engage with people who had proven themselves to be generous. This bias was the result of several factors: (1) older adults had worse associative memory for how much each person had shared, possibly due to an age-dependent decrease in neural activity in the medial temporal lobe (MTL) during encoding, (2) older adults had a stronger tendency to re-engage with familiar over novel faces regardless of their past behavior, and (3) while activity in value-responsive brain regions tracked with how generous a face looked across the age range, older adults were less able to inhibit the influence of these irrelevant perceptual features when it was necessary to do so. In line with this behavioral effect, younger adults showed greater activation in the inferior frontal gyrus (IFG) during choices that required suppressing irrelevant perceptual features in favor of associative memory. Taken together, our findings highlight age-dependent changes in both the ability to encode relevant information and to adaptively deploy it in service of social decisions.