[TheSisb2]

I've read of some people who were finally set free after a long stretch in solitary confinement, and many of them attributed the preservation of their sanity to simple math or word exercises. I believe one would just count exponents of two as far as he could go and another would try remembering every word in every language they knew.

Not sure of similarities to brain training games, but I would bet there is something there.

[executesorder66]

You just gave me an interesting idea. Manually writing down my vocabulary (grouped into passive and active) for every language I know. Counting up the results and comparing would be rather interesting.

After that diffing it with a dictionary file for each language to see the gaps.

This will probably take forever, but it could be worth the time.