Scientists in the U.S. say they have discovered a way to make the brain reverse the damage it suffers after a stroke, and are optimistic that it will lead to treatment which will exploit the body’s ability to heal itself.

Along with heart disease and cancer, strokes are one of the biggest killers and although the death rate has fallen in recent years, the condition still claims many lives.

The researchers found in experiments on rats whose brains had been starved of oxygen to simulate the effects of a stroke, fewer were left paralysed after the treatment, which activated stem cells in their brains.

Professor Ronald McKay and a team from the U.S. National Institute of Neurological Disorders and Stroke examined the adult stem cells in the rats’ brains and stimulated a receptor known as “notch”, on the stem cells.

The researchers found that it caused reactions that produced new brain cells and say notch is important in all tissues and the beneficial effects may involve responses in cells of the vascular, immune and nervous systems.

The treatment improved the ability of existing cells to survive the lack of oxygen and when rats were given the treatment, many recovered from the loss of movement they suffered with the stroke.

The discovery will raise hopes for new treatments for stroke by using the body’s own stem cells to encourage healing and has wide implications for stem cell research.

Other treatments using embryonic stem cells have been restricted because implanted cells come under attack from the body’s immune system.

More than 150,000 people in the UK have a stroke every year which equates to one every three minutes.

Although most occur in people over 65, anyone can have a stroke, including children and even babies.

Strokes are more common in men than women and is the third most common cause of death in the UK and is the most common cause of severe disability.

More than 250,000 people live with disabilities caused by stroke; about a third of people who have strokes suffer from some form of disability.

There are two main types of stroke and the most common is an ischaemic stroke, which happens when a clot blocks an artery carrying blood to the brain.

The second type is called a haemorrhagic stroke, which is caused when a blood vessel bursts and causes bleeding into the brain.

Signs of a stroke include facial, arm or leg weakness, speech problems and a partial loss of vision.

A healthy diet, regular exercise, not smoking and ensuring blood pressure is normal, can help prevent a stroke.

The study is published in the magazine Nature.