1. Norwegian National Headache Centre, Department of Neuroscience, Norwegian University of Science and Technology, and Trondheim University Hospital, Trondheim, Norway
2. Danish Headache Centre, Glostrup University Hospital, Copenhagen, Denmark
3. Department of Neurology, University Hospital Essen, Germany
4. Department of Neurology, Albert Einstein College of Medicine, New York, USA
5. Preventive Medicine and Biometrics, Uniformed Services University, Maryland USA
6. Division of Neuroscience and Mental Health, Imperial College, London, UK