[1] Univ Duisburg Essen, Dept Neurol & Headache Ctr, D-45147 Essen, Germany
[2] Univ Calif Los Angeles, David Geffen Sch Med, Dept Neurol, Los Angeles, CA 90095 USA
[3] Kings Coll London, NIHR Wellcome Trust Kings Clin Res Facil, London WC2R 2LS, England