Scientists have found a way to make the brain reverse the damage it suffers after a stroke, raising hopes for treatment able to exploit the body's ability to heal itself. Their experiments used rats whose brains had been starved of oxygen to simulate the effects of a stroke. Strokes kill brain cells and affect the way the body works, with paralysis common. Ronald McKay, of the US National Institute of Neurological Disorders and Stroke, in Maryland, in the US, studied the adult stem cells in the rats' brains. He stimulated a receptor known as "notch", on the stem cells, and found that it caused reactions that produced new brain cells. Compared with untreated rats, fewer of the rodents that had a stroke and the stem cell therapy were left paralysed.