At a delightful school last week, three of us authors heard (twice, no less) the classic question from a middle-schooler: Where do you get your ideas? We've all heard this one a thousand times, of course. The Enlightenment poets pursued their muse with ceremonies and rituals. We writers of today trick ourselves by going to coffee shops, attending retreats, stimulating our brains with caffeine or conventions.
Kate Elliot has written a very nice little post on the topic on SFNovelists: http://www.sfnovelists.com/2009/02/18/creativity/ She nails it pretty well, and raises a good point about tracking the idea process with a brain scan. In fact, brain scans on creative people look different from those on noncreative people. Classical musicians' brains operate differently from, for example, engineers' brains.
There's a great old opera joke about why tenor brains are so expensive. It's something about how they've never been used, so they're worth more. (Sorry all you tenors. Just substitute "coloratura soprano" if it bothers you.) Seriously, though, I often wonder if it's the brain at all that serves up ideas. It feels more mysterious than that, even mystical. And I wouldn't hesitate to light a candle at midnight under a full moon if it would tempt my muse to pour forth her riches.