Mismatch negativity (MMN) is a neurophysiological indicator of the brain's ability to extract relevant information from an irrelevant background. The P3a orienting response often accompanies MMN in deviance detection paradigms. Both MMN and P3a have been described as reliable biomarkers of schizophrenia. MMN/P3a impairments are associated with deficits in verbal memory and attentional switching, reflecting dysfunctions in the temporal and frontal systems, respectively. It remains unresolved whether MMN/P3a are robust biomarkers of psychosis in first-episode patients. Thirty-four young people (18 to 30years) were assessed in this study; 17 first-episode psychosis (FEP) patients were compared to 17 healthy controls. To elicit MMN/P3a, a two-tone passive auditory oddball paradigm with 8% duration deviants was used; event-related potentials were recorded at frontal, central and temporal (mastoid) sites. Neuropsychological assessments included processing speed, attentional switching, simple attention, and verbal learning and memory. Social functioning and quality of life measures were also obtained. The FEP group showed significantly reduced MMN amplitudes compared to controls. The FEP group also showed significantly reduced P3a amplitudes at frontal and central sites compared with controls. As expected, the FEP group also showed significant deficits in attention and verbal learning/memory. Correlational analyses found strong associations between fronto-central MMN/P3a peak amplitude and cognitive/psychosocial functioning. This study provides evidence of early neurobiological markers in young people with FEP. These findings suggest that MMN/P3a impairments are present at early stages of psychosis and that fundamental pre-attentive/deviance detection deficits may mark the beginning of progressive underlying changes with illness onset. Such deficits in FEP appear to have important links with higher-order cognitive and psychosocial functioning.
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