What is the brain doing when it is being asked to do nothing in particular?

During the past five years, Marcus Raichle and his team at the Washington University School of Medicine in St. Louis have looked at that question. While working on other neuroimaging studies, Raichle noticed an interesting trend in brain activation when experimental participants began a cognitive task.

While some areas of the brain would “light up” during the task, other areas would show marked deactivation. Even more surprising, the deactivation pattern seemed to be very consistent in the medial regions of the brain, including the posterior cingulate and precuneus.

 “This was not random noise,” Raichle says. “And given that the majority of what the brain does is just flat-out function—just the brain running itself, really—we started thinking about what was really going on in there.”

 Raichle suggests that this highly organized state of brain areas is a “default network,” responsible for the intrinsic functional activity of the brain, as opposed to thought specifically evoked by a stimulus or cognitive task.

 “Your brain is a very expensive gadget to run,” he says. “If you aren’t engaged in a task, your brain doesn’t just turn off. It wouldn’t make any sense.”

 The use of imaging techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have provided neuroscientists with the ability to map specific areas of the brain and correlate them with behavior. But what about when there is no specific behavior to map?