A colleague who was a notable football player in his day has been slowly losing the connection between thinking and speaking. As best I can tell, his brain still works just fine, but it's increasingly difficult for him to speak coherently, particularly off the cuff. He's in his late 60s, but he's a smart, proud man, and it's hard to watch.
I listened to this http://www.bbc.co.uk/programmes/b05102tf last month. It was very convincing.