Ventromedial prefrontal cortex supports prototype representations in healthy older adults

The ability to learn broad concepts from individual instances is relevant throughout our lifespans as new concepts enter the world, and we seek to acquire new skills and hobbies that can enrich our lives. While older age has been associated with declines in the ability to remember individual instances, less is known about how these declines impact concept learning and generalization or the neural systems that older adults recruit to support abstraction. In the present study, young and older adults completed a category learning task while undergoing fMRI. We fit formal prototype and exemplar models to behavioral and brain data - models that differentially index concept learning based on abstraction versus memory for individual category members. We found that the fit of both models to behavior was poorer in older adults, but older adults were more likely than young adults to be best fit by the prototype model and less likely to be best fit by the exemplar model. We also found that young and older adults recruited anterior hippocampus and VMPFC to a comparable degree to support prototype-based generalization. In contrast, older adults showed weaker old/new discrimination of category members in a set of occipital and parietal regions. These results suggest that the age-related increase in prototype reliance in behavior may be driven by declines in memory for specific exemplars coupled with a relatively intact neural system for representing prototypes.