What do you think about the research that says that solving crosswords only improves your solving crosswords ability and nothing more i.e., memorizing a deck of cards might only improve your performance on that particular task and everything else is just an illusion?
> See brain-derived neurotrophic factor, which will be elevated after many exercise, be them of mental origin or just walking.
Just because they share some biological commonalties (of course they do! How could it be otherwise?) doesn't make them meaningfully the same thing, any more than them both having lots of mitochondria does.