A stroke is a heart attack in a person's head; an interruption of blood caused either by a clot or a rupture in one of the millions of blood vessels that feed the brain.

Either way, brain cells die, resulting in any number of symptoms, from partial paralysis to loss of speech or vision, depending on the location of the damage.

An estimated 700,000 Americans suffer from stroke annually, and 150,000 die, making it the third leading cause of death in the United States, behind heart failure and cancer.

Strokes are a major cause of physical disability and dementia.