High intensity dependence of auditory evoked dipole source activity indicates decreased serotonergic activity in abstinent ecstasy (MDMA) users - Tuchtenhagen,F.; Daumann,J.; Norra,C.; Gobbele,R.; Becker,S.; Pelz,S.; Sass,H.; Buchner,H.; Gouzoulis-Mayfrank,E. (Neuropsychopharmacology, 2000)