1. University of Regensburg, Germany
2. Kiel Headache Center, Germany
3. RWTH Aachen University, Germany
4. University of Halle, Germany
5. University of Essen, Germany
6. University of Tübingen, Germany
7. University of Würzburg, Germany
8. Helios Klinikum, Erfurt, Germany
9. University Medical Center Hamburg-Eppendorf, Germany