Physical activity is one of the most important means of reducing risk of dementia. And new strategies are needed to support older adults in becoming more active. This study will test whether a new cross-generational intervention increases physical activity in adults over 60. The participants are at a high risk for dementia and are currently part of the PREVENT-AD longitudinal cohort at McGill University. This research will also reveal the brain circuits and processes underlying successful lifestyle change at the individual level. Overall, this study’s findings will help to further develop the right dementia-risk intervention for the right person at the right time.