1. Center for the Study of Human Cognition, Department of Psychology, University of Oslo, 0317 Oslo, Norway
2. Department of Radiology
3. Department of Psychiatry
4. Department of Neuroscience, University of California, San Diego, La Jolla, CA 92093, USA
5. Clinical Neurochemistry Laboratory, Department of Neuroscience and Physiology, Sahlgrenska Academy, Göteborg University, SE-431 80 Mölndal, Sweden