[1] Charite, Dept Neurol, CVK, D-13353 Berlin, Germany
[2] Charite, Dept Neurosurg, CVK, D-13353 Berlin, Germany
[3] Inst Neurol, Sobell Dept Motor Neurosci & Movement Disorders, London WC1N 3BG, England
[4] Kings Coll Hosp London, Dept Neurosurg, London, Denmark
[5] Radcliffe Infirm, Dept Physiol Anat & Genet, Oxford OX2 6HE, England
[6] Radcliffe Infirm, Dept Neurol Surg, Oxford OX2 6HE, England
[7] Katholieke Univ Leuven, Dept Neurol, Louvain, Belgium
[8] Katholieke Univ Leuven, Dept Neurosurg, Louvain, Belgium