[1] Stavanger Univ Hosp, Norwegian Ctr Movement Disorders, POB 8100, N-4068 Stavanger, Norway
[2] Stavanger Univ Hosp, Dept Phys Med & Rehabil, Stavanger, Norway
[3] Stavanger Univ Hosp, Dept Res, Stavanger, Norway
[4] Univ Bergen, Dept Clin Med, Bergen, Norway
[5] Haukeland Hosp, Dept Neurol, N-5021 Bergen, Norway
[6] Newcastle Univ, Inst Ageing, Inst Neurosci, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England
[7] Stavanger Univ Hosp, Dept Neurol, Stavanger, Norway