1 Dept of Neurology and Danish Pain Research Center, Aarhus University Hospital, 8000 Aarhus C, Denmark.
2 University of Oslo, Norway; Department of Pain Management and Research, Oslo University Hospital, Oslo, Norway.
3 University of Oslo, Norway; Department of Pain Management and Research, Oslo University Hospital, Oslo, Norway; Department of Anaesthesiology, Oslo University Hospital, Oslo, Norway. Electronic address: harald.breivik@medsin.uio.no.