I think human brains work better in cold climates. Think how many great inventions were created in warm climates. Not many.
Even in hot countries, air conditioning is the key to a lot of cerebral productivity. I certainly couldn't go through a Queensland summer without it.
I know 18th and 19th century painters used to travel to Italy, but that was for the light, not necessarily to get their noggins into gear. The Romantic Poets used to travel to the med just to indulge their poncey notions of themselves and to escape whatever plague was hanging over England.
All the serious stuff was done once they got back home.
So that's what it is! I thought it was my brain cells dying off and here it's just the climate - thanks for that, Malc.