A virtual reality for flies: A new method for measurements in behaving animals

Our researchers have developed a new experimental setup that allows to perform measurements in walking flies. The fly itself is tethered, but “walks” on a air-supported ball and its environment changes in real time according to its own movements. The fly thus "walks" in its own virtual reality. Using this new experimental setup, the researchers demonstrated that flies can memorize and find a specific place. Furthermore, the virtual reality setup also opens up the possibility for robust recordings of the tiny fly neurons while the animal is behaving in a natural way.

We all know how difficult it is to catch a fly. Flies have an outstanding visual sense. The fruit fly Drosophila exhibits a wide range of visually controlled behaviors and often serves as a model organism in neurobiological research. For example, it is able to remember specific locations based on visual cues - an amazing performance for the fly's tiny brain. Researchers have long been trying to understand what lies behind this impressive memory performance at the neuronal level. One major difficulty, however, is that stable measurements of nerve cells in a freely walking fly have so far been impossible.

Johannes Seelig, head of the research group "Neural Circuits", and his group member Andres Flores-Valle, together with the MPINB's in-house mechanical workshop, have developed a new experimental setup that overcomes this difficulty. A tethered fly is placed in the middle of an experimental arena with optical landmarks that can be rotated around several axes. A small air-supported ball is placed underneath the fly allowing the fly to "walk" on this ball in any direction. The ball’s movements are recorded and translated so that the entire virtual environment rotates around the fly in real time corresponding to its own movement. To specifically study the fly's ability of place learning, the team employed a classical approach taking advantage of a fundamental mechanism: Heat quickly becomes dangerous to the small organism. To avoid overheating, flies therefore learn the location of a cool place very quickly. They recognize this place by means of optical landmarks. Since the fly does not actually move in the virtual reality setup, the researchers use a trick: They heat up the entire walking fly using an infrared laser. Once the heat source is switched off, the fly remembers the looks of this supposedly cooler location and, after several test runs, is able to find it ever more quickly and with fewer detours. These results thus demonstrate that the flies indeed show natural behavior in this new experimental setup.

In another recent paper, Johannes Seelig's group has already shown that they are able to record over a very long time from brain neurons of a tethered fly walking on a ball. The group now aims to combine these two methods to measure do long-time neuronal recordings from flies in the virtual reality setup. They hope to unravel the fundamental neuronal mechanisms and networks behind various insect behaviors.

To the publication (full text acces until August 20, 22)