1. Department of Social Sciences, University of Salamanca, Salamanca, Spain,
2. Department of Neurology, University Hospital '12 de Octubre ', Madrid, Spain, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Madrid, Spain
3. Department of Neurology, University Hospital 'La Paz ', Madrid, Spain
4. Department of Neurology, Hospital Quirón Madrid, Pozuelo de Alarcón, Madrid, Spain
5. Department of Neurology, University Hospital 'Pío del Río Hortega ', Valladolid, Spain
6. Department of Neurology, Hospital 'Mancha-Centro ', Alcázar de San Juan, Ciudad Real, Spain
7. Bayer Schering Pharma AG, Barcelona, Spain