1. Laboratory of Psychophysiology and functional Imaging, Department of Psychiatry, Psychosomatics & Psychotherapy, University of Wüerzburg; Fuechsleinstr. 15, D-97080 Würzburg, Germany, 2Department of Biological and Clinical Psychology, Friedrich Schiller University Jena, Am Steiger 3//1, D-07743 Jena, Germany, and 3Institute of Medical Psychology and Systems Neuroscience, University of Muenster, Von-Esmarch-Str. 52, D-48149 Muenster, Germany