Contradictory behavioral effects of neuronal perturbations on behavioral responses to linearly polarized light in freely walking Drosophila

Many insects can use the polarization of the skylight as a navigational cue. As shown previously, freely walking Drosophila orient along the e-vector of linearly polarized UV light presented both dorsally and ventrally. We are interested in the neuronal mechanisms leading to this behavior, and specifically how the central complex and its inputs are involved. We investigated the behavior of flies exposed to linearly polarized near-UV light (400 nm) presented dorsally. Flies walked freely in a circular, flat arena surrounded by a heat barrier. Using the GAL4-UAS genetic system, we drove the expression of the potassium inward rectifier KIR2.1 to perturb each of several different neuron types of the polarization vision pathway. Perturbing EPG compass neurons in the central complex slightly weakened average alignment and increased its variability. On the other hand, when two different GAL4 lines driving expression in the ER4m ring neurons, identified by connectomics as the major polarization inputs to the fly central complex, were perturbed, the alignment strength increased. A similar effect was observed when the inputs to ER4m, the TuBu _a neurons, were perturbed. We did not predict EPG and ER4m perturbations to cause opposite effects. Further investigation would be required to understand the physiological mechanisms of these contradictory behavioral effects.