Neurophysiological and neuropsychological evidence for attentional dysfunction in schizophrenia

The behavior of the P50 wave of the auditory evoked potential in a paired stimulus or conditioning-testing paradigm has been used as a measure of sensory gating disturbance in schizophrenia. Schizophrenics fail to decrement the P50 response to the second stimulus of the pair, so that the ratio of the test to the conditioning amplitude is elevated over normal values. The aim of this study was to compare this neurophysiological measure to neuropsychological measures of attention and memory. As expected, schizophrenics performed worse than controls on most measures. The time to complete a digit cancellation test, a measure of sustained attention, was found to be particularly longer in schizophrenics than in control subjects. Furthermore, the increased time to complete this task correlated with the increased ratio of the amplitude of the test P50 response to the conditioning response in the schizophrenics. Thus, a neurophysiological defect in sensory gating may relate to a disorder in sustained attention in schizophrenia. Although the P50 wave may come from the hippocampus, neuropsychological measures of verbal learning and memory were not correlated with alterations in the P50 ratio.