1. Pain Medicine Center, Swiss Paraplegic Center, Guido A. Zäch-Strasse 1, 6207 Nottwil, Switzerland
2. Clinica de Dor, R. São João de Brito 610, 4100-455 Porto, Portugal
3. Department of Anesthesiology and Palliative Care, Radboud Medical Center, Geert Grooteplein Zuid 10, 6525 GA Nijmegen, The Netherlands
4. Department of Anesthesiology and Pain Medicine, University of Porto Alegre, Porto Alegre 90050-170, Brazil
5. PBDL, Institute Biology, Leiden University and Fytagoras BV, Sylviusweg 72, 2333 BE Leiden, The Netherlands
6. Science Department, University College Roosevelt, P.O. Box 94, 4330 AB Middelburg, The Netherlands