Do fruit flies dream of electric bananas?

摘要

A fruit fly hovers in mid-air. bulbous eyes capture a panoramic view of the world, but it ignores most of what it sees. Instead, it is captivated by one small thing: a bright green stripe that just zipped by. It's worth a closer look, worth landing on. The fly chases after it. Or so it thinks. The fly is actually in a laboratory and suspended on a wire inside a miniature flight simulator. Surrounding the fly is a cylindrical LED screen, and travelling around that screen is a vertical stripe of green light. Each time the stripe comes into view, the fly tries to steer towards it. Sensors count the fly's wing beats, measure its orientation, and control the motion of the stripe accordingly. If the fly steers hard enough, it can halt the stripe and hold it steady in its view. It's a neat gizmo, but watching it work I discover there's more to it than that. Inserted in the fly's brain is an electrode, and buzzing through that electrode, scrolling across a computer screen, are some curious brainwaves. Whenever the fly steers towards the stripe, these saw-tooth waves grow taller, and when the fix is lost, they shrink.