But scientists say that in order to explain the human brain, they'll have to learn a lot more about much smaller and simpler brains, like those in mice and insects and worms. "What you need is access to circuits and cells, and that probably means not in humans," says professor Leslie Tolbert of the University of Arizona neuroscience department.

For example, scientists are using fruit flies to figure out why many people with autism are easily overwhelmed by loud sounds, bright lights, strong odors or simply being touched.

Rachel Wilson, a neurobiologist at Harvard, suspected that this sensory overload might be caused by a malfunction in brain circuits that adjust the "volume" of sensory signals. But there's no easy way to study that in people. So she turned to fruit flies, which use a similar volume-control system to process odors.