Alzheimer's disease is one of the most common degenerative mental illnesses, affecting approximately 500,000 people in the UK. In the first of a new series, Peter Evans talks to Professor Steven Rose about new research that might allow us to reclaim lost memories. Therapies that slow the rate of memory loss are already available. Might we reach a point when you could pop into the local chemist and buy what's been dubbed "Viagra for the brain"? Producer John Watkins