the secret to an effective fly treadmill is getting the air pressure right. You need just enough to keep the fly’s walking surface—a smooth ball about the size of a pea—spinning freely, but not so much that it starts to gyrate.
Gaby Maimon’s Laboratory of Integrative Brain Function didn’t invent the fly treadmill. But their work, alongside others’ in the field, has taken it to the next level, enclosing it in a visual virtual-reality environment and training cameras on the ball that allow them to observe Drosophila melanogaster’s navigational decisions while simultaneously recording neural activity in neurons.
Members of the Maimon lab carve the ball out of foam using a homemade tool akin to a melon baller, then ink the markings with a Sharpie and balance it atop a custom-machined air jet nozzle that lets it rotate freely. Tracking software, adapted from code written by colleagues in Australia, is fed by cameras trained on the ball’s markings.
The treadmill setup allows Maimon and his colleagues to ask sophisticated questions about how the brains of their tiny subjects calculate angles, keep track of where they’ve been, and avert danger.