The purpose of this study is to clarify the benefits to brain health and thinking processes that result from different forms of exercise. This study will examine the effectiveness of cybercycling (virtual reality enhanced stationary cycling) for persons at risk for and with MCI, and compare this with the individual cognitive, behavioral, and physiological effects of physical and mental exercise alone. The Investigators hypothesis that cognitive benefit will be greatest for combined aerobic and cognitive exercise compared to physical and mental exercise alone.