Coding of sky-compass information in neurons of the anterior optic tubercle of the desert locust Schistocerca gregaria
The primary aim of my Doctoral thesis project was to test through intracellular recordings the hypothesis that the lower unit of the AOTu participates in polar- ization vision. Four types of interneurons with ramifications in the lower unit of the AOTu were characterized in multiple recordings...
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|Zusammenfassung:||The primary aim of my Doctoral thesis project was to test through intracellular recordings the hypothesis that the lower unit of the AOTu participates in polar- ization vision. Four types of interneurons with ramifications in the lower unit of the AOTu were characterized in multiple recordings. All of these neurons were sensitive to polarized light, sub- stantiating our hypothesis (Chapter I, -> page 19). Two types of neuron, called lobula tuber- cle neuron (LoTu1) and tubercle tubercle neuron (TuTu1), were especially amenable to intracel- lular recordings, due to their large axon diam- eters. In the first set of experiments, we found that all polarization-sensitive neurons were also responsive to unpolarized light (Chapter I, -> page 19). To investigate the significance of this finding, we extended the stimulation with un- polarized light in a second set of experiments. The responses of both LoTu1 and TuTu1 to UV and green light spots from different directions suggest that these neurons signal the horizontal direction of the sun (solar azimuth), by exploit- ing both intensity- and color-gradients as well as the sky-polarization pattern (Chapter II, -> page 35). The use of both unpolarized and po- larized light information to detect the solar az- imuth can result in conflicting information pro- vided by the different cues. One way to reduce this conflict of information is to exclude certain areas of polarized skylight from being analyzed by the polarization-vision system. By stimulat- ing with different degrees of polarization (d), we showed that the threshold for E-vector detec- tion lies around d-values of 0.3. This means that an area of around 100 degrees around the sun con- tains no visible E-vector information for these neurons (Chapter III, -> page 51). Recent be- havioral experiments further confirmed that the pathway described above is vital for polarotaxis in locusts. Tethered locusts that are flown under a slowly rotating polarizer show periodic changes in yaw torque with a period of 180 degrees (Mappes & Homberg, 2004). When the anterior optic tract is unilaterally transected, the locusts are still able to respond to the rotating E-vector in the same manner as intact animals. However, when the DRA that is contralateral to the transection site is occluded, the animals become disoriented (Mappes and Homberg, in revison).|