It's a condition people have suffered and studied for thousands of years. Once thought to be a result of angering the gods, or being struck down by a curse, stroke involves a sudden paralysis, loss of speech or - in the most dramatic version - loss of consciousness altogether.
We now know that it's caused by loss of oxygen supply to brain cells, when either a clot blocks the small blood vessels in the brain or a haemorrhage means blood no longer gets to that part of the organ. But we're still not much better at reversing its effects.
However, we can keep stroke sufferers alive for a lot longer. Former Israeli prime minister, Ariel Sharon (right), was in a coma after suffering a massive stroke caused by a brain haemorrhage in January. He's still being kept alive in hospital.
We're also much better at teaching people how to find alternative pathways to take over the jobs performed by the parts of the brain that have been damaged by the stroke. That's what speech physiotherapists and occupational therapists are good at.
But one new option is to give people known to have strokes a drug, tPA, that can dissolve clots. However, there's a risk. This drug can also cause bleeding in the brain. So in trying to solve one problem by dissolving the clot, you may create a bigger problem: a brain haemorrhage.
This is what seems to have happened to Sharon. He was given the clot-busting medicine to treat an earlier episode, had a major haemorrhage, and was left comatose.
However, at a meeting of the American Stroke Association last month, two different teams of experts described how they've been able to drip the clot-busting tPA directly onto clots in the brain, and been able to reverse the stroke in a significant number of patients.
They located the blockage, then put a catheter into the blood vessels and fed it right up to where the clot stopped the blood flowing. Then they released a dose of tPA directly onto the clot until it dissolved. In quite a few cases, the results were remarkable, with the brain-damage symptoms - loss of speech and movement - disappearing when the clot was dissolved. There are, however, a lot of 'buts' in this story. Before doctors can consider doing this, they have to have all the right equipment - brain scanners, catheters, and above all, skill and experience.
The clot has to be in the right place, doctors have to be sure the trouble is caused by a clot, and the stroke has to be diagnosed early (within an hour or two of the blockage happening).
This is where recognising the signs of a possible stroke (sudden loss of speech ability, confusion, weakness on one side of the body, drooping on one side of the face, dizziness or fainting) can make a lot of difference.
Elderly people, those with known heart disease, smokers and the overweight are all more likely to have strokes, as are diabetics, people with high blood pressure, or from families where a lot of relatives have suffered them.