The bee central complex - the neural substrate for path integration? (#109)
To navigate their environment, animals have to identify behaviorally relevant features in their surroundings and obtain information about their relative position to them. In migratory insects polarized skylight is used to compute body orientation within the central complex (CX), a widely conserved brain structure. We ask whether this principle is valid across insects, how it is modified between species, and which other cues are integrated with body orientation information. We specifically target two bee species, the nocturnal sweat bee Megalopta genalisand the diurnal bumble bee. Both species differ fundamentally in their sensory environment, but exhibit the behavioral strategy of central place foraging. An LED-based virtual reality apparatus, in which an artificial sky is combined with a 360 ̊ LED arena, has allowed us to electrophysiologically analyze responses of CX-neurons to skylight compass cues and to begin illuminating which other visual features are processed in the CX. We have confirmed that polarized light is indeed represented in CX-neurons of nocturnal and diurnal bees, even though these species are no long-distance migratory insects. Additional to the representation of directional information in cells of the CX, we also identified neurons that specifically respond to translational optical flow. These cells are located in the noduli, a small compartment of the CX of previously unknown function. Interestingly, bees use translational optic flow to measure the distance travelled on a foraging trip. Therefore, these results suggest that such distance information is relayed to the CX of bees and converges with directional information. This convergence of compass and odometer information is a prerequisite for successful central place foraging and we thus hypothesize that the bee CX serves as the neural substrate for path integration.