[1] Maudsley Hosp & Inst Psychiat, Dept Old Age Psychiat, London SE5 8AZ, England
[2] Newcastle Gen Hosp, Reg Neurosci Ctr, Dept Neurochem, Newcastle Upon Tyne NE4 6BE, Tyne & Wear, England
[3] UCL Royal Free & Univ Coll Med Sch, Dept Psychiat & Behav Sci, London, England