Stroke is a condition which occurs when the brain is deprived of oxygen – for example, due to a blood clot blocking an artery – causing the death of neural cells. Individuals who have had a stroke may have difficulty with movement, speech, and eating. The damage, and recovery, varies with the extent and location of the stroke. Some individuals recover well with therapy, while others are left with severe disabilities. Scientists are using stem cell models to understand how damaged brain tissue might be repaired, and whether stem cell transplants might one day be used to repair brain tissue damaged by a stroke.