• appetitive
• conditioning
• drosophila melanogaster
• Gal4 lines
• learning
• memory
• navigation
• optogenetics
• virtual reality

Learning has been successfully studied by quantifying changes in the behavior of an animal in a controlled environment. However, it has been hard to find direct links between observations and neural representations. One way to address this problem is to use head fixed animals and measure neural activity while they are preforming a task. This thesis focuses on an attempt to establish a visual appetitive conditioning paradigm in virtual reality (VR), for Drosophila melanogaster, suitable for in vivo imaging experiments, a novelty in the field. There are three main reasons why to employ the fruit fly: the genetic access to small subsets of neurons, the limited size of its brain and the relative complexity of its behaviors. By studying appetitive conditioning we can understand whether the fly is able to make causal links between its action and a desired result. We employed a two-dimensional (2D) virtual world made of a forest of cone and cylinder shaped landmarks, which the animal could explore. We aimed to train flies in the virtual world by pairing cone visits to a short reward (train trial), and we quantified learning by comparing the behavior of the fly in VR before and after the training (pre and post trial). The reward was delivered optogenetically by activating those neurons expressing a fructose receptor, which has been proofed to have a positive valence for the animal. Here we show that, during training, flies get exposed to the reinforcer at very high frequencies for short periods of time. Furthermore, we do not observe a shift in the difference in frequency of visits between the landmarks. Instead, the difference in length of visits changes after training, in favor of cones. Therefore, we can argue that the reward delivery could have not successfully reinforced visits to cones, but likely it reinforced the presence of the animal around the rewarded landmark. Further investigations are required to understand this learning process.