Visual processing clue to schizophrenia risk

By Eleanor McDermid, Senior medwireNews Reporter

An element of the event-related potential (ERP) response to visual stimuli is impaired in patients with prodromal symptoms of schizophrenia, research suggests.

The amplitude and peak latency of the P300 wave, which is an endogenous ERP component associated with a person's reaction to a stimulus, were significantly reduced in patients with prodromal symptoms, as well as in those with schizophrenia, relative to in controls.

Margaret Niznikiewicz (Harvard Medical School, Brockton, Massachusetts, USA) and colleagues obtained the findings from electroencephalogram recordings taken from 23 prodromal patients, 17 first-episode schizophrenia patients, and 31 healthy controls while they undertook a visual oddball task.

The ERP differences were present in parietal and occipital regions, but not in frontal and central regions. The researchers say previous evidence suggests that parietal and inferior temporal areas contribute to the visual P300. "Based on this evidence, P300 deficits in posterior and occipital channels found in the present study may imply functional or structural alterations in the parietal and temporal brain areas" in the prodromal as well as schizophrenic patients, they suggest.

Furthermore, in the prodromal group, the reduction of P300 amplitude was associated with the severity of prodromal symptoms.

Niznikiewicz et al also found that the amplitude of the N1 component (first negative peak in response to stimulus) was significantly reduced in the schizophrenia patients versus the controls, but not in the prodromal patients.

"These findings suggest that early sensory processing likely localized to visual sensory regions is not severely compromised in high-risk subjects but becomes abnormal after the first psychotic episode," write the researchers in Schizophrenia Research. They say that more work is needed to determine at what point in the prodromal phase the N1 component becomes abnormal.

By contrast, P1 (first positive peak) amplitude was not reduced in either group. The team says that reductions in P1 are likely task-specific, and probably only revealed by tasks targeting the magnocellular pathway, whereas N1 reduction is state-dependent.

"We conclude that visual P300 has a potential to be used in a population-based studies to detect subjects with compromised cognitive function that might suggest vulnerability for schizophrenia," say the researchers.

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