[1] Univ Maryland, Sch Med, Dept Neurol, Baltimore, MD 21201 USA
[2] Natl Hosp Neurol & Neurosurg, London WC1N 3BG, England
[3] UCL, Inst Neurol, London, England
[4] Dept Vet Affairs Med Ctr, Neurol Serv, Baltimore, MD USA
[5] Dept Vet Affairs Med Ctr, Res Serv, Baltimore, MD USA