The body has a way to protect you when you have dreams; it paralyzes you. Otherwise, what happens in these patients is that the system fails. So when they're dreaming they're running away, they're moving around, thrashing around. Sometimes they injure themselves and fall out of bed, sometimes they injure their partners. This is called REM sleep behaviour disorder. It's not that common, but what's amazing about this discovery is that half the people who have this disorder turn out to develop Parkinson's disease in the next ten years or so. That's an enormous percentage. This is something we've learned only in the last few years.
What this tells you is two important things. First, it's not only the part of the brain we thought that's affected in Parkinson's disease—it's probably much more widespread. There are other centres in the brain that are affected, and they are affected earlier than the movement centres. Second, it gives you the potential to identify these people early. They could be candidates, if there are new treatments that come along, to get at the disease before 70% or 80% of the neurons have degenerated.