1. Turku PET Centre, University of Turku and Turku University Hospital, Turku, Finland
2. Department of Psychology and Logopedics, Abo Akademi University, Turku, Finland
3. Aging Research Center, Karolinska Institute, Stockholm, Sweden
4. Department of Radiation Sciences, Umea University, Umea, Sweden
5. Department of Neurology, Turku University Hospital, Turku, Finland.