[1] John Radcliffe Hosp, FMRIB Ctr, Oxford OX3 9DU, England
[2] Stanford Univ, Dept Neurol, Stanford, CA 94305 USA
[3] Univ London Imperial Coll Sci Technol & Med, Dept Clin Neurosci, London, England
[4] Vrije Univ Amsterdam, Med Ctr, Dept Radiol, Amsterdam, Netherlands
[5] Leiden Univ, Med Ctr, Dept Radiol, Leiden, Netherlands
[6] Leiden Univ, Med Ctr, Inst Psychol Res, Leiden Inst Brain & Cognit, Leiden, Netherlands