Altered Hemispheric Asymmetry of Auditory Magnetic Fields to Tones and Syllables in Schizophrenia

Background: A growing body of literature suggests that schizophrenicpatients often do not show the normal brain hemispheric asymmetry. We have found this for simple tones presented to the right ear in a previous study. In this study we extended this investigation to left ear stimulation and verbal stimuli. Methods: With a whole-head neuromagnetometer, con­ tra- and ipsilateral auditory-evoked magnetic fields in response to tones (1000 Hz) and to the syllables ("ba") delivered to the left and right ears in separate runs were compared between schizophrenic patients (n = 17) and healthy control subjects (n = 15). Results: In response to tones, all control subjects showed the expected asymmetry (contralateral predominance) of the auditory-evokedmagnetic NI00m (dipole moment). In the patient sample asymmetry was reversed following tones presented to the left ear in 47% andfollowing tones to the right ear in 24%. In response to syllables, the asymmetry was similar between groups. In patients com­ pared with control subjects the NI00m was located more anterior without asymmetry between hemispheres. Conclusions: Results suggest that deviation from the normalfunctional lateralization in schizophrenia appears in a proportion of patients at a basic stage of auditory processing, but may be compensatedfor at higher levels such as the processing of syllables. BioI Psychiatry 2001; 49:694-703 © 2001 Society ofBiological Psychiatry