1. Herchel Smith Laboratory for Medicinal Chemistry, University of Cambridge School of Clinical Medicine, Forvie Site, Robinson Way, Cambridge CB2 2PZ, UK
2. Physiological Laboratory, University of Cambridge, Downing Site, Downing Street, Cambridge CB2 3EG, UK
3. Oxford Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
4. The Wolfson Brain Imaging Centre, University of Cambridge, Box 65, Addenbrooke's Hospital, Cambridge CB2 2QQ, UK