1. Department of Anesthesia, Critical Care and Pain Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA
2. Danish Headache Center, Department of Neurology, Rigshospitalet Glostrup, Denmark
3. Hartford Healthcare Headache Center, Ayer Neuroscience Institute, West Hartford, CT, USA
4. University of Connecticut School of Medicine, Farmington, CT, USA
5. Harvard Medical School, Boston, MA, USA