Diminished responsiveness of ERPs in schizophrenic subjects to changes in auditory stimulation parameters: implications for theories of cortical dysfunction.

Event-related potentials (ERPs) were recorded from 15 schizophrenic patients and 17 normal controls in an auditory oddball paradigm in order to investigate the effects of stimulus probability and interstimulus interval (ISI) on deficits in mismatch negativity (MMN) generation in schizophrenia. MMN amplitude was reduced for schizophrenics overall, with the degree of deficit increasing as deviant probability decreased. In contrast, schizophrenic subjects were no more affected by alterations in ISI than controls. The experimental design also permitted evaluation of N1 generation as a function of ISI in schizophrenia. Schizophrenic subjects showed decreased N1 amplitude across conditions, with the degree of deficit increasing with increasing ISI. For both MMN and N1, therefore, the degree of deficit increased with increasing component amplitude in normals, implying that the deficit in ERP generation in schizophrenia may reflect a decrease in maximal current flow through underlying neuronal ensembles. The observed pattern of dysfunction is consistent both with observations of impaired precision of processing in schizophrenia, and with predictions of the PCP/NMDA model.