Cold Spring Harbor
Ensemble coding and odor perception: Ca imaging of odor-evoked neural activity in the mushroom body of living Drosophila brain
We are investigating olfactory coding in Drosophila, as the first step towards the studying of olfactory learning and memory. We finally have developed a preparation that allows to monitor population neuronal activities via imaging recorded from mushroom bodies of living flies. Mushroom body neurons (2500 of them in flies) are two synapse away from the olfactory receptor neurons and are critical for insect olfactory learning. Since the sensitive dye can be loaded into all neurons, we are able to monitor activities of all these neurons simultaneously via optical recordings. It was indicated that specific patterns of spatially distributed activities were evoked by different odorants and different concentrations of the same odorant. This concentration-dependent distributed pattern of neuronal activity is eliminated in a mutant specifically for one, but not other odors tested. In other words, different concentrations of this odor produced the same pattern of activity in this mutant. Behaviorally, the concentration-dependent attraction of this odor to flies is absent in the mutant. Thus, the result suggests that the odor quality and intensity are encoded by the patterns of neuronal activity in the brain and these patterns are necessary for odor perception.