I'm not sure what's behind the Brain Training DS boom. I don't believe it's the Wii interation that did it though. I'm going to take a guess than the DS spent another week over 200k, and that the Wii slipped just under 100k.
A reason for the Brain Training DS boom could also be the commercials "buy your mom a DS lite for mother day". A game like Brain Training along a DS lite for mom would make sense.
Anyway, let's wait for the numbers, before me make conclusions.