[1] Frenchay Hosp, Dept Neuropathol, Bristol BS16 1LE, Avon, England
[2] Frenchay Hosp, Dept Neurosurg, Inst Clin Neurosci, Bristol BS16 1LE, Avon, England
[3] Hammersmith Hosp, MRC, Ctr Clin Sci, London W12 0NN, England
[4] Hammersmith Hosp, Imperial Coll, Fac Med, Div Neurosci, London W12 0NN, England