Response to the first stimulus determines reduced auditory evoked response suppression in schizophrenia: single trials analysis using MEG.

OBJECTIVE: Reduced auditory evoked response (AER) suppression in a paired-stimulus paradigm may index genetic liability for schizophrenia. In most published studies of AER suppression, scores are based on data averaged over numerous stimulus presentations and recorded from few channels. It is unclear whether averaged data are equally representative of single trial responses in normal and schizophrenia subjects. In the present report, we used 148 channel magnetoencephalography to investigate grand-average and single trial responses on AER suppression.
METHODS: The typical paired-stimulus paradigm was used to evoke time-locked AERs from 20 normal and 20 schizophrenia patients. Gamma band response (GBR) and low frequency response (LFR) characteristics were measured on grand-averaged and single trial data. Generalized eigenvalue decomposition was used to reduce the multiple channel information to a vector that accounted for the most AER variance for the GBR and LFR.
RESULTS: Group performances on grand-average and single trials were similar. A remarkable difference, which replicates previous studies, was that schizophrenia subjects had smaller LFR amplitudes in response to the first stimulus than normal.
CONCLUSIONS: These findings are inconsistent with the "poor suppression" theory often used to explain schizophrenia-normal group differences when using the paired-stimulus paradigm.