RESUMO
Decreased P300 amplitude has been reported in schizophrenics during their first episode. The brain sources that contribute to this abnormality have not yet been well documented, and were investigated in the present study using high density EEG recordings. Nineteen drug-naive first episode schizophrenics were compared to 25 normal controls. Auditory P300 was elicited using an oddball paradigm. The brain sources of P300 ERP were reconstructed by performing low resolution of electromagnetic tomography (LORETA) analysis. No group difference in P300 latency was found. P300 amplitude was smaller for schizophrenics than for controls. Topographical analysis revealed that P300 amplitude reduction in schizophrenics was significant over left and medial regions of interest (ROIs). LORETA analysis of the P300 peak revealed that, the brain sources of P300 were symmetrically distributed over left and right hemispheres among the normal controls, but were asymmetrically distributed among the patients, with a reduction predominantly over the left temporal area. Statistical non-Parametric Mapping analysis identified 29 voxels of a significant group difference, which focused on left insula, left superior temporal gyrus (STG) and left postcentral gyrus (PCG). In addition, the mean P300 current source density over left insula, left STG and left PCG correlated inversely with the patients' Positive and Negative Syndrome Scale scores. The neural substrates that contributed to the decreased P300 amplitude in drug-naive first episode schizophrenia relatively focused on left STG and its nearby areas. These areas are probably involved in the pathogenesis of schizophrenia, and possible mechanisms for pathology need to be further clarified.