Homberg Lab - Dipl.-Biol. Tobias Bockhorst

Several neurophysiological and neuroethological observations indicate that insects can use visual landmarks (i.e. objects at learned positions relative to a target such as a food source) for spatial orientation. The underlying neuronal processing probably includes forming and memorizing associations of visual object representations with position-invariant directional information.

The desert locust (Schistocerca gregaria) seems to be capable of deriving directional information for navigational purposes from the polarization pattern of skylight. Directions of polarization vectors in the zenith are related to the course of the solar meridian. Integrating these directions with additional cues that allow discriminating between the solar and antisolar hemisphere may provide compass information that could serve landmark-based orientation.

Mutant studies in Drosophila revealed that certain types of neuron in the fly brain’s central complex are essential for visual landmark-based orientation. From electrophysiological experiments in the desert locust we know that neurons arborizing in this area of the insect brain are tuned to characteristic directions of polarization vectors. Interestingly, we also observed responses to patterns of unpolarized light in these neurons. Thus we assume that they may serve landmark-based orientation by integrating visual object features with directional information inherent in polarization vectors.

My dissertation project aims at further pursuing this hypothesis. I measure the spiking activity of individual neurons in the central complex of the desert locust under presentation of both polarized light and different object-like patterns of unpolarized light.

Furthermore I investigate whether neurons in the central complex exhibit tuning to spectral properties which may allow discriminating between the solar and antisolar hemisphere. Integration with such spectral information may lend a compass-like quality to a representation of polarization vector space which has been found in the desert locust’s central complex, thus providing a robust basis for navigational capabilities.

The morphology of electrophysiologically probed neurons will be reconstructed based on tracer injections. Digital co-registration with formerly reconstructed neurons arborizing in the same respective brain region is used to identify likely partners in the central complex network. Moreover, microanatomical characterizations can serve the distinction between axonal and dendritic neurites, thus providing cues on the direction of informational flow in the network.

• Publications
  
• Theses