Multichannel electroencephalographic assessment of auditory evoked response suppression in schizophrenia

Reduced auditory evoked response (AER) suppression in a paired-stimulus par adigm (where suppression equals the difference between S1 and S2 amplitudes divided by S1 amplitude) may index genetic liability for schizophrenia. Th e present report is a multiple-channel electroencephalographic (EEG) study of AER suppression among 20 normal and 20 schizophrenia subjects. The typic al paired-stimulus paradigm was used to evoke time-locked AERs. AER respons es were scored at P50 and N100 in the time domain using both single (Cz) an d multichannel data (after reduction using principal components analysis, P CA), and were scored for information in the gamma (20-50 Hz) and low-freque ncy (1-20 Hz) ranges using multichannel information (also after PCA). The t ime domain analyses demonstrated that schizophrenia patients differ from no rmal in amplitude of response to the first, but not to the second, stimulus for both P50 and N100. The frequency domain data demonstrated that schizop hrenia patients differed from normal on amplitude of the low-frequency resp onse (LFR) to the first, but not to the second, stimulus. The groups did no t differ significantly on amplitudes of the gamma-band responses. Group sep arations were largest for the multichannel N100 and LFR data, with the LFR demonstrating, a modestly better risk ratio for differentiating schizophren ia from normal subjects. The present results suggest two novel differences from previous AER suppression studies: (1) S1 amplitudes largely determine differences between normal and schizophrenia groups on AER suppression, and (2) frequency domain analyses may provide important complimentary informat ion when studying AERs in schizophrenia.