Cognitively Normal

The investigators will compare \[18F\]-PI-2620 tau PET scans from patients with frontotemporal lobar degeneration (FTLD), patients with non-amnestic presentations of Alzheimer's disease (naAD), and demographically matched cognitively normal subjects.

This is a single-arm, two-visit, non-randomized, cross sectional study identified as an intervention due to the use of a single bout of aerobic exercise to assess cerebrovascular function under the NIH rules. This study is not masked and its primary purpose is to develop a basic science understanding of the relationship between cerebrovascular health and balance control with aging. This study will involve 102 individuals classified as younger adults, middle-aged adults, and older adults who are neurotypical and cognitively normal. The primary outcome from a clinical trials perspective will be cerebrovascular response to a bout of aerobic exercise (i.e. change in cerebral blood flow with the performance of aerobic exercise on a recumbent stepper exercise machine). Non-interventional outcomes will be EEG measures of cortical activity and biomechanical kinetic and kinematic data recorded during standing balance reactions, as well as biological blood samples for genomic analysis.