What? There's "dark energy" in the brain? Not in mine I hope! Actually, it's not as bad as it sounds. There is an article out now in the journal Science (requires subscription, get the gist here), where the author Marcus E. Raichle from Washington University at St. Louis explains that most of our brains' energy budget is spent on spontaneous, intrinsic activity and only a small fraction on responding to external stimuli. He further notes that brain activity is notoriously variable and usually many brain scans have to be averaged in order to get an accurate idea of where the brain is processing what. This evidence is well in line with the notion that brains may actually be more output/input systems than input/output machines. Brains constantly compute a model of themselves in their environment in order to be able to predict future events. Maybe this constant computation is what requires so much energy? Of course, these computations are exactly at the heart of operant conditioning, so it's no wonder this article piqued my curiosty

This is an image showing the areas of correlated activity in the resting (no input) human brain.