Let's clear this up - the creatures in Left 4 Dead are NOT after your brains. They aren't zombies, they are the infected. Valve Software though? They totally want to have a root around inside your grey cells.
In piece written for Edge magazine, Valve's Gabe Newell spoke about how Left 4 Dead's AI Director analyses a player's actions to gauge how well they are faring and adjusts the game to suit. The kind of user input data that can be captured from a mouse or gamepad doesn't give the level of detail that Newell would like to see, though, so Valve are researching ways of using biometrics and even EEG's to examine a gamer's inner state.
"There are new technologies where we can wire players up with EEGs and actually have direct exposure to their physical reactions to the games," writes Newell.
"We can know for sure of something is actually frightening the player - their heart rate is going up, their respiration stats are peaking, appropriate parts of their brains are being activated. Direct measurement of players' arousal states and responses to the things we're doing is super exciting. It just will allow us to be much more analytical about the decisions that we're making and the roller coaster ride we're trying to create for the player."
What kind of kit this will require you to buy remains a mystery, of course. I can just about stomach having a fake drum kit in my living room - having a brain scanner lurking next to the sofa might be a gadget too far.
Gabe Newell Writes for Edge [Edge]