These results demonstrate impaired frontotemporal cortical networks for preattentive detection of change in speech sounds in schizophrenia. The language-related dysfunction in schizophrenia may be present at the early stage of auditory processing of relatively simple stimuli, such as phonemes, and not just at stages involving higher-order semantic processes.

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To reveal the spatiotemporal characteristics of the auditory automatic discrimination process, mismatch negativity (MMN) generators were assessed with a high-resolution EEG system (128ch) and scalp current density (SCD) analysis. Ten normal volunteers participated in the study. Event-related potentials were recorded during a selective attention task. Sequential SCD mappings revealed that a current sink/source combination in the left temporal regions and a current sink in the right frontotemporal regions appeared around 200 msec irrespective of the ear of stimulation. Moreover, a parietal sink/source combination was demonstrated on the right hemisphere around 240 ms irrespective of the ear of stimulation. These findings demonstrate that the auditory automatic change detection process is, both spatially and temporally, a multiple-generated system.

In order to examine the effects of risperidone on cognitive impairment in schizophrenia, event-related potentials (ERPs) were recorded before and after switching from conventional neuroleptics to risperidone in schizophrenic patients. ERPs were recorded during two auditory discrimination tasks (an oddball task and a distraction task) in 10 medicated schizophrenic patients during conventional neuroleptic and risperidone treatments. The amplitudes and latencies of N 100 and P300 component were measured in ERPs for target stimuli in the oddball task and in ERPs for target and novel stimuli in the distraction task. Although N 100 amplitude and latency and P 300 amplitude did not change significantly after switching the drug compared to that during conventional neuroleptic treatment, P 300 latency for target stimuli shortened significantly during risperidone treatment in both tasks, accompanied by the shortening of the reaction time in the distraction task. The P 300 latency change did not correlate with the change of the severity of psychopathology. These findings suggest that risperidone may speed the information processing in schizophrenic patients, contributing to the improvement of cognitive functions.

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