1. Umeå Center for Functional Brain Imaging , Umeå University, 901 87 Umeå , Sweden
2. Department of Integrative Medical Biology , Physiology Section, Umeå University, 901 87 Umeå , Sweden
3. Department of Radiation Sciences , Diagnostic Radiology, Umeå University, 901 87 Umeå , Sweden
4. CINEICC , Faculty of Psychology and Educational Sciences, University of Coimbra, Rua do Colégio Novo, 3001-802 Coimbra , Portugal