Stroke: Dr. Greg Albers, Director of the Stroke Center at Stanford University, discusses stroke. A stroke occurs when there is sudden disruption of blood flow to the brain. This can occur from a blood clot in the brain, or rarely bleeding in the brain. Risk factors for stroke include high blood pressure, diabetes, high cholesterol, heart disease, smoking, advanced age, and race. Blood thinners, such as aspirin, can prevent stroke. Symptoms include weakness, slurred speech, and confusion.