here
It seems he's in the early stages of Alzheimer's disease.
His press statement is really funny and typical though:
"I will, of course, be dead at some future point, as will everybody else," he said.
"For me, this may be further off than you think. It's too soon to tell.
"I know it's a very human thing to say 'is there anything I can do', but in this case I would only entertain offers from very high-end experts in brain chemistry."