The body receives most of its essential substances through the circulation of blood. That’s what got University of California, San Francisco researchers curious about testing the rejuvenating capabilities of young blood in old animals. Study leader Saul Villeda compares the role of blood to a highway.

"If you really think about blood, it has different exits to different tissues, but it connects every tissue in your body. So how are tissues going to communicate? How is the liver going to tell, maybe the muscle, or how is the brain going to communicate, then, with the liver? It's going to be through the highway, and that highway is blood. We're taking sort of the communication that's occurring in a young animal and then putting it into the communication that's occurring into the old animal."

Villeda says that the old mice that received young blood showed improved cognitive performance such as responding quicker to environmental stimuli.

"By introducing these players from the young blood, all of a sudden, we're changing the entire sort of systemic environment, and that's causing an effect on multiple organs within the body."