Impaired temporal lobe processing of preattentive auditory discrimination in schizophrenia

Feature-specific stimulus discrimination related to short-term auditory sensory memory can be studied electrophysiologically using a specific event-related potential (ERP) component termed mismatch negativ-ity (MMN), which is generated in the auditory cortex, indexing automatic comparison of the existing mem-ory trace to incoming novel stimuli. Previous results with electroencephalography (EEG) and magnetoen-cephalography (MEG) suggest that schizophrenia patients have attenuated MMN response and that preattentive auditory processing preceding MMN appears to be functionally asymmetric in schizophre-nia. Here we studied parallel MMN activity of the hemispheres using a whole-head MEG by presenting stimulus blocks consisting of frequent standard and infrequent deviant tones to 15 schizophrenia patients and 19 healthy control subjects. Auditory evoked fields (AEFs) were recorded simultaneously over both audi-tory cortices. The equivalent current dipole (ECD) modeling revealed that patients had significant MMNm reduction (magnetic counterpart of MMN) in both temporal lobes. In addition, patients had signifi-cantly delayed MMNm in the left but not in the right hemisphere to ipsilateral auditory stimuli. These results suggest that patients with schizophrenia have impaired auditory processing in the temporal lobes underlying preattentive stimulus discrimination that is also selectively delayed in the left hemisphere