[1] Herlev Hosp, Lab Pain Physiol, Dept Anaesthesiol, DK-2730 Herlev, Denmark
[2] Univ Calif San Francisco, Dept Neurol, Pain Clin Res Ctr, San Francisco, CA 94143 USA
[3] Univ Calif San Francisco, Dept Anesthesia, Pain Clin Res Ctr, San Francisco, CA 94143 USA