1. Headache and Facial Pain Group, UCL Queen Square Institute of Neurology, Queen Square, London, UK
2. Headache and Facial Pain Group, The National Hospital for Neurology and Neurosurgery, Queen Square, London, UK
3. Mathematics Institute of Orsay, Paris Sud University, Orsay, France
4. Department of Neurology, St Olav’s University Hospital, Trondheim, Norway
5. NTNU (University of Science and Technology), Department of Neuromedicine and Movement Science, Trondheim, Norway
6. Norwegian Advisory Unit on Headaches, Trondheim, Norway