1 Danish Research Center for Magnetic Research (DRCMR), Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Kettegaard Allé 30, 2650 Hvidovre, Denmark; Umeå Centre for Functional Brain Imaging (UFBI), Umeå University, Sweden; Centre for Demographic and Aging Research (CEDAR), Umeå University, Sweden. Electronic address: cj@drcmr.dk.