Devil's Advocate: It is as much stimuli as it is culturally ingrained into us. No definitive answer either way. But I will always lend weight to stimuli over metaphysical entity.
The most likely reason for our reactive prayers is as a stress relief mechanism. Shit, it could be a genetic tie in with how long humans have been around.
I have it and I'm a sound man who lives a life without a creator, yet... If I'm not bargaining with some invisible entity I would be freaking out a lot more.
Some would insinuate that being drunk at 9 in the morning to be signs of serious issues. Me? I'd insinuate it as signs of no plans and a refrigerator full of Whiskey and Guinness.
Re: Can an atheist pray?