Reduced laterality of the source locations for generators of the auditory steady-state field in schizophrenia

Reduced hemispheric asymmetry of evoked field generators in schizophrenia in secondary auditory cortex has been replicated with mixed success. This disparity is possibly due to the complex nature of the 100-msec generators typically investigated. In this study, we evaluated a source located in primary auditory cortex, responsible for the steady-state response, to determine whether similar asymmetries were present. Contralateral evoked fields were recorded with a 37-channel neuromagnetometer in response to 40-Hz pulse trains. Dipole models were used to localize the sources in both hemispheres of schizophrenic subjects ( n = 17) and normal control subjects ( n = 18). Control subjects were asymmetrically lateralized, with sources in the right hemisphere approximately 6 mm further anterior than those on the left. In contrast, schizophrenic subjects showed no significant difference between hemispheres. The findings support theories linking schizophrenia to disturbed asymmetry of temporal lobe function. The steady-state response, having a more discrete Heschl’s gyrus generator location, may be better suited for evaluating auditory asymmetry.