Reduced plantar sensation can lead to weakened balance ability in elder adults and an addition of cognitive tasks will further weaken it. Thereby, we attempted to explore the brain activity pattern of the elder and of young adults under foot stimuli and in dual-task condition. The results revealed that elder adults have significantly stronger cortical excitability than young do, and that foot stimuli induced stronger cortical excitability compared with dual-task condition. In conclusion, these phenomena may be due to the elder adults’ inadequate central reserve. Besides, added cognitive task can further reduce the brain’s response through diminished sensory input.