A group of researchers, led by Bruce M. Spiegelman, Stanley J. Korsmeyer Professor of Cell Biology and Medicine at the Dana-Farber Cancer Institute and Harvard Medical School, found a new kind of hormone  in the muscles during the process of exercise of animal and people. The hormone produced by exercise can be released into the bloodstream and then flows to and crosses the blood brain barrier. The new hormone is named irisin, after the messenger god Iris in Greek mythology. Spiegelman believes that this newly found hormone is the critical component that explains how and why exercise can help cognition. Large-scale epidemiological studies also indicate that active people tend to be much less likely to develop Alzheimer’s disease and other forms of dementia than people who exercise infrequently.