1. Max Planck Institute for Biological Cybernetics; Tuebingen Germany
2. IMPRS for Cognitive and Systems Neuroscience; Eberhard-Karls University of Tuebingen; Germany
3. Department of Physics; Eberhard-Karls University of Tuebingen; Germany
4. Department of Biomedical Magnetic Resonance; Eberhard-Karls University of Tuebingen; Germany
5. Department of Physics; University of Greifswald; Greifswald Germany