[1] UCL, Dementia Res Ctr, Inst Neurol, London WC1N 3BG, England
[2] London Sch Hyg & Trop Med, Med Stat Unit, London WC1, England
[3] Natl Hosp Neurol & Neurosurg, Dept Clin Neurol, London, England
[4] Vrije Univ Amsterdam, Med Ctr, Dept Neurol, Amsterdam, Netherlands
[5] Imperial Coll Sci Engn & Med, Div Neurosci & Mental Hlth, Fac Med, London, England