I think the assumption here is that one would be continually learning new material. While crosswords help with exercising pattern recognition and recall, you'r

I think the assumption here is that one would be continually learning new material. While crosswords help with exercising pattern recognition and recall, you're not generally learning anything 'new' (except the occasional word, and this diminishes over time). Sight-reading random piano sheets, for example, would exercise most if not all of your faculties