[1] BAKKEN RES CTR,MAASTRICHT,NETHERLANDS
[2] KATHOLIEKE UNIV LEUVEN,DEPT NEUROL,LOUVAIN,BELGIUM
[3] TECH UNIV MUNICH,DEPT CLIN NEUROPHYSIOL,D-8000 MUNICH 80,FED REP GER
[4] KAROLINSKA HOSP,DEPT NEUROSURG,S-10401 STOCKHOLM 60,SWEDEN
[5] KATHOLIEKE UNIV LEUVEN,DEPT NEUROSURG,LOUVAIN,BELGIUM
[6] STOKE MANDEVILLE HOSP,NATL SPINAL INJURIES CTR,AYLESBURY,BUCKS,ENGLAND