Neuronal processing of sky compass information in the brain of bees
Final Report Abstract
Honeybees use sky‐compass cues like the sun, the sky polarization pattern and a color gradient across the sky for spatial orientation. While in other insect species the neuronal basis for this ability has been extensively targeted by research, only very little is known in bees. The current project therefore aimed at understanding aspects of the sky compass system of bees at different levels of the brain. Towards this goal, we employed two different methods to measure neuronal activity: calcium imaging and intracellular recordings. Calcium imaging experiments targeted the anterior optic tubercle, a brain region that is part of the sky compass pathway and lies between peripheral neurons of the optic lobe and the compass network in the central complex. We were able to establish two photon calcium imaging recordings from the anterior optic tubercle in behaving honeybees. Bees were walking on an air supported ball in an LED arena while neuronal activity was monitored through calcium‐sensitive dyes. Under these conditions bees showed goal‐directed walking towards a vertical stripe and actively re‐established their heading direction when the vertical stripe was displaced by the experimenter. While our data base of calcium imaging experiments is not big enough to draw any firm conclusions yet, our experiments prove, that behavioral experiments including visual stimulation can be combined with calcium imaging in honeybees. When compass neurons are stimulated with polarized light with a rotating angle of polarization, their response maxima are different during clockwise and counterclockwise rotations of the polarizer. Using intracellular recordings, we examined if these differences are dependent on rotation direction. We surprisingly found that the angular difference in tuning is bigger, the slower the angle of polarization rotates and can be up to 60°. This has important implications for the directional coding during natural flight. When flying a turn, insects do this in a discontinuous way. Instead of constantly changing heading direction throughout the turn, like an airplane, they switch between short turns at high velocity and segments of straight flight, which is believed to aid them in depth perception. An internal compass system must be able to keep up with these rapid turns. To test how the compass system in the brain of bees performs under naturalistic conditions, we changed the rotation of the polarizer from continuous rotation to a naturalistic movement pattern taken from the literature. Despite abrupt rotations at angular velocities of up to 550°/s, the compass neurons in the bee brain reliably showed very similar spiking patterns during each display of the stimulus. These experiments show that the compass network in the central complex is well adapted to the flight behavior of bees and stimulated further experiments into the dynamical properties of sky‐compass neurons in bees.
Publications
- (2016). Microglomerular synaptic complexes in the sky‐compass network of the honeybee connect parallel pathways from the anterior optic tubercle to the central complex. Front Behav Neurosci 10, 186
Held, M., Berz, A., Hensgen, R., Muenz, T. S., Scholl, C., Rössler, W., Homberg, U. and Pfeiffer, K.
(See online at https://doi.org/10.3389/fnbeh.2016.00186) - (2019): Calcium imaging in tethered behaving honeybees. 111 th Annual Meeting of the German Zoological Society, Greifswald, Germany. Poster NB 9
Held M, Haberkern H, Deo C, Lavis, L Jayaraman V, Pfeiffer K
