Sharpen your memory. Part 5, Broken memories.

The fifth in a six-part series in which Mariella Frostrup looks at how our memory defines who we are. In this part we look at what happens when memory starts to degenerate, and if anything can be done to slow the slide experienced by some into dementia. Mariella speaks to actor Harriet Walter who lost both parents to dementia, scientists Dr. Kim Graham, Professor Michael Kopelman and David Clegg.