86 Fig. 6 Time course of MMN activity in nanoampere meters at the four sources for the frequency-deviant stimuli (baseline =solid line, low dosage=dotted line, high dosage=dashed line; means; p values from post-hoc tests; n=9) 1 e c r u o s 2 e c r u o s 3 e c r u o s 4 e c r u o s Psychopharmacology (2008) 199:77–88 S-ketamine DMT not significant low dose < baseline (p=0.043) not significant not significant high dose < baseline (p=0.017) low dose < baseline (p=0.027) high dose < baseline (p=0.017) high dose < baseline (p=0.024) not significant MMN in the healthy control group (Todd et al. 2008). Baldeweg et al. (2002) found a pronounced reduction in MMN at frontocentral electrodes in patients with schizo- phrenia in the presence of normal activity at mastoid electrodes and concluded that the frontal generators of MMN may be preferentially affected in schizophrenia. However, our descriptive data suggest that S-ketamine affected the frontal and temporal sources of MMN genera- tion. Since magnetoencephalography (MEG) predominantly detects the temporal sources of MMN generation (Rinne et al. 2000; Rosburg et al. 2004), the MEG findings of reduced MMN activity in schizophrenia (Kreitschmann-Andermahr et al. 1999; Pekkonen et al. 2002) also support the involvement of temporal sources in reduced MMN activity