Patients with schizophrenia show attention deficits. The frontal P2a and posterior N2b event-related potential components are early indices of activity in neural systems supporting attention and they are reduced in schizophrenia in auditory tasks. However, the auditory P300 is reduced as well. Thus, the P2a and N2b reductions may simply reflect a general event-related potential amplitude reduction. The visual P300, however, is often spared in schizophrenia. If neural systems supporting attention are specifically disrupted in schizophrenia, the attention-sensitive P2a and N2b should be differentially reduced in patients, compared with the P300, in a visual attention task.
We analyzed 64-channel event-related potentials from 14 schizophrenic patients and 14 control subjects in a visual object–spatial attention task. We examined the amplitude of the P2a, N2b, and P300 components in the target minus standard difference wave to see if there was a differential reduction of the P2a and N2b compared with the P300.
Both the P2a and N2b waveforms were reduced in the patient group (81%[control mean, 1.99 µV; patient mean, 0.38 µV] and 95% [control mean, 0.55 µV; patient mean, 0.03 µV], respectively) while the P300 was not reduced. Measured at the peak of the frontal P2a, the N2b was larger dorsally in the spatial task and larger ventrally in the object task in the control group.
The spatial distribution of the P2a and N2b was consistent with activity in the prefrontal cortex and modality-specific posterior cortex, respectively. The differential reduction of the P2a and N2b waveforms supports the hypothesis of specific disruption in neural systems of visual attention in schizophrenia.