Age-related differences in trust decisions: when memory fails and appearances prevail.

Older adults are frequent victims of scams, possibly due to biases in how they decide whom to trust. Indeed, older adults' decisions are more likely to be influenced by how generous a person looks and less so by their memory for how this person behaved. Here, we leverage functional magnetic resonance imaging data to clarify the mechanism by which this age-dependent difference emerges. Eighty-six participants learned how much of a $10 endowment an individual shared in a dictator game, and then made decisions about whom to play another round with. As we hypothesized, older adults did not reliably prefer to re-engage with people who had proven themselves to be generous. This bias was driven by a combination of worse associative memory for how much each person shared, linked to decreased medial temporal lobe activity during encoding, and decreased inhibition of irrelevant facial features, linked to reduced activity in the inferior frontal gyrus. Taken together, our findings highlight 'age-related differences' in the ability to both encode relevant information and adaptively deploy it in service of social decisions.