The researchers said the early introduction of the cells might even interrupt the typical "chain reaction" of tissue damage which follows a stroke, in which the initial injury harms additional cells in surrounding areas.

BBC: Stem cell 'first aid' for rat stroke

And, also like fuel cells, that initial application may now be found in the specialised needs of space travel.

ECONOMIST: A more efficient way to make electricity in spacecraft

At least half of the damage, however, occurs hours later, as the initial injury sets off a complex and poorly understood chemical cascade that disables surrounding cells.

FORBES: Repairing The Brain

So even if their initial trials do work, there will be no way of telling for sure which group of cells is responsible.

FORBES: Cell makers

Another theory is that the initial illness may have created an autoimmune reaction, causing the body's immune system to attack normal cells as if they were foreign substances.

CNN: Post-polio syndrome