My understanding is that it's about building complex neural networks that your brain can use as a backup when others fail (although that's probably a massive ov

My understanding is that it's about building complex neural networks that your brain can use as a backup when others fail (although that's probably a massive oversimplification). Crosswords are too simple, they only teach you how to get better at crosswords. Learning an instrument is a whole lifestyle - you need to combine aural, verbal, proprioception, social, and so on.