Comment by PaulRobinson

The Test is repeated every day you get in the cab.

If you get into a black cab in London and ask to be taken to any location, anywhere within 6 miles of Charing Cross, that driver will know immediately the right route to take without satnav. To get to that point they need to know 25,000 streets and many, many landmarks - statues, museums, galleries, restaurants, hotels, and so on.

I used to regularly drink with a cabbie in London, and he said that every time somebody got in the back his heart rate would rise, as he'd realise he's "on" and about to have to work out where to head from scratch. Within 30 seconds he'd have every step of the way worked out, down to which lanes at which intersections, no matter where in London he was or where he was going.

That's the thing that's likely going to reduce Alzheimer's.