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, we used prototype-based category learning as a domain to test age differences in concept learning. Young and older adults completed a category-learning task while undergoing fMRI. We fit formal prototype and exemplar models to behavioral and brain data to 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. While only young adults showed significant prototype-tracking in the hippocampus, both young and older adults recruited the ventromedial prefrontal cortex (VMPFC) to support prototype-based generalization. Although evidence for age differences in prototype representations emerged in a whole-brain analysis, evidence for age differences were weak in the VMPFC and hippocampus. Thus, engagement of the VMPFC prototype-learning system may help maintain concept generalization in older adults.