[1] Max Planck Inst Biol Cybernet, Dept Physiol Cognit Proc, D-72076 Tubingen, Germany
[2] Univ A Coruna, Dept Quim Fundamental, La Coruna 15008, Spain
[3] Max Planck Inst Neurol Res, In Vivo NMR Lab, D-50931 Cologne, Germany
[4] Max Planck Inst Dev Biol, Dept Biochem, D-72076 Tubingen, Germany
[5] Univ Manchester, Dept Imaging Sci & Biomed Engn, Manchester M13 9PT, Lancs, England
[6] Max Planck Inst Biol Cybernet, MR Neuroimaging Agents Grp, D-72076 Tubingen, Germany