1. Department of Neurology , Vestfold Hospital , Tønsberg , Norway
2. Faculty of Medicine , University of Oslo , Oslo , Norway
3. Norwegian Centre for Violence and Traumatic Stress Studies , Oslo , Norway
4. Department of Neuroscience, Faculty of Medicine , Norwegian University of Science and Technology , Trondheim , Norway
5. Norwegian National Headache Centre , Section of Neurology, St. Olavs Hospital , Trondheim , Norway
6. HUNT Research Centre, Department of Public Health, Faculty of Medicine , Norwegian University of Science and Technology , Trondheim , Norway
7. Department of Neurology , Oslo University Hospital , Ullevå, Oslo , Norway
8. National Centre for Spinal Disorders , St. Olavs Hospital , Trondheim , Norway