Strokes happen when blood flow to your brain stops. Within minutes, brain cells begin to die. There are two kinds of stroke. The more common kind, called ischemic stroke, accounts for approximately 80 percent of all strokes. It is caused by a blood clot that blocks or plugs a blood vessel in the brain (see illustration at right). The other kind, called hemorrhagic stroke, is caused by a blood vessel that breaks and bleeds into the brain.

Transient ischemic attacks (TIAs) are "mini-strokes" that occur when the blood supply to the brain is briefly interrupted. A TIA is a stroke that comes and goes quickly. It happens when a blood clot blocks a blood vessel in your brain. Symptoms of a TIA are like other stroke symptoms, but do not last as long. Most symptoms of a TIA disappear within an hour, although they may last for up to 24 hours. Because you cannot tell if these symptoms are from a TIA or a stroke, you should get to the hospital quickly. TIAs are often a warning sign for future strokes.

NINDS conducts stroke research and clinical trials at its laboratories and clinics at the National Institutes of Health in Bethesda, MD., and in nearby hospitals; and through grants to major medical institutions across the country. Currently, NINDS researchers are studying risk factors for stroke and how brain damage results from a stroke. Basic research has also focused on the genetics of stroke, stroke risk factors, and how to protect the brain against damage during a stroke. Scientists are also working to develop new and better ways to help the brain repair itself to restore important functions after a stroke. New advances in imaging and rehabilitation have shown that the brain can compensate for function lost as a result of stroke.