Neuronal processing of sky compass information in the brain of bees

• Applicant: Professor Dr. Keram Pfeiffer
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 264066771

Many animals possess a time-compensated sun compass, which enables them to infer a fixed earthbound direction, eg. to a nest, from the continually changing solar azimuth. Scattering of sun light in the atmosphere leads to a color gradient and a pattern of polarized light along the sky. Both phenomena are spatially directly linked to the solar azimuth. In addition to the direct view of the sun, they can therefore be exploited to infer the solar azimuth. For more than six decades, bees have been used as model organisms for sky compass orientation in behavioral experiments. However, the neuronal basis underlying this fascinating behavior has so far remained enigmatic. The goal of this project is to elucidate the processing of navigationally relevant polarized and chromatic visual cues in the brain of bees, using neurophysiological techniques. Due to the abundance of behavioral data available, their rather simple brain (compared to vertebrates), and the unique possibility to keep these animals outdoors, i.e. under natural light conditions, bees lend themselves to these experiments like no other species. Two questions form the core of this proposal. 1. How are polarized and unpolarized light stimuli integrated in the brain of these animals? 2. What are the dynamic properties (both circadian and on the ms-s timescale) of the sky compass system? During sky compass navigation, the brain has to solve a highly sophisticated task. On one hand, all available pieces of information regarding solar azimuth have to be integrated (orientation of polarized light stimuli, azimuth and color of unpolarized light stimuli). On the other hand the animal has to be able to differentiate between sun, sky, and clouds at all times. For example when the sun itself is not visible a sunlit cloud should not be erroneously interpreted as the sun. By stimulation with different polarized and unpolarized light stimuli the underlying mechanisms will be elucidated using intracellular recordings. In the second part of the project, long- and short-term changes of neurons of the sky compass system will be investigated. Calcium imaging and extracellular recordings will be used to monitor diurnal changes and the influence of neuroactive substances on these. Using intracellular recordings will allow me to investigate short-term changes in neuronal tuning that are elicited through dynamic visual stimuli, as experienced during flight. The outcome of this project will provide insight into fundamental neuronal principles underlying sensory processing of navigationally relevant visual stimuli.

• DFG Programme: Research Grants