As both a gamer and a student of neuroscience, this fascinates me. This Science article is from way before the birth of CrunchGear, but you know us: any excuse to post, right?
You may be familiar with the Tetris Effect: after playing Tetris (or Bejeweled, or Solitaire) for a while, you can’t get those pieces/gems/cards out of your head, and as you lay in bed they float in front of your eyes like ghosts of wasted time past. Well, some researchers were studying this effect (I know not why) and discovered that people with severe amnesia would also experience the Tetris effect — despite not remembering they’d ever played the game. I don’t think these findings are quite as applicable to something like World of Warcraft (it’s more the systematic and pattern-based nature of Tetris that makes it persist as a mental image), but just to be safe, no one tell Jack Thompson about it.