Implicit memory, including priming, can be preserved in aging and dementia despite impairment of explicit memory. To explore the neural correlates of preserved memory ability, whole-brain functional MRI (fMRI) was used during a repetition priming paradigm to study 34 young adults, 33 older adults without dementia, and 24 older adults in the early stages of dementia of the Alzheimer type (DAT). Both older adult groups showed repetition-based response time benefits (priming) and changes in activation along inferior frontal gyrus similar to those shown by young adults. Across all three groups, repetition-related response time reductions correlated with prefrontal activity reductions, demonstrating a direct relation between priming and fMRI-measured activity change. These results suggest that despite difficulties with deliberate memory, both older adults without dementia and those with early-stage DAT can modify behavior mediated by prefrontal contributions, making these preserved abilities an attractive target for cognitive training and rehabilitation.