1. Department of Psychology, Centre for Lifespan Changes in Brain and Cognition, University of Oslo, Oslo 0317, Norway
2. Umeå Centre for Functional Brain Imaging, S-90187 Umeå, Sweden
3. Physiology Section, Department of Integrative Medical Biology, Umeå University, S-90187 Umeå, Sweden
4. Department of Radiation Sciences, Diagnostic Radiology, Umeå University, S-90187 Umeå, Sweden
5. Department of Radiology and Nuclear Medicine, Oslo University Hospital, 04024 Oslo, Norway