Will it ever be possible to repair our brains? So far this has proved impossible, but new research is causing brain scientists to feel that at last progress is beginning to be made.

In Sweden, two patients suffering from Parkinson's disease have had cells from their own adrenal glands transplanted into their brains - and more transplant operations are to follow. In animals, living tissue has been successfully transplanted into their brains to treat failing memory. "Horizon" reports on the latest research which one day might lead to the solution of one of the greatest challenges in medical science.