Mind your mind: Alzheimer's disease

There are 25 million people in the world suffering from Alzheimer's disease and the figure is forecast to double every 20 years. It's now believed that the changes in our brains that lead to the disease may begin decades before the symptoms appear. What are the early signs, and how can you distinguish them from the natural memory loss that comes with ageing? We also hear from a woman who cares for her husband with Alzheimer's and an Australian scientist who's developing a promising new drug that may stop the disease from progressing.