Temporal variability and spatial diffusion of the N2 event-related potential in high-functioning patients with schizophrenia

Recent theories of schizophrenia have proposed a fundamental instability of information processing on a neurophysiological level, which can be measured as an increase in latency variability of event-related potentials (ERPs). If this reflects a fundamental deficit of the schizophrenic illness, it should also occur in high-functioning patients. These patients have also been observed to show a more diffuse activation pattern in neuroimaging studies, which is thought to reflect compensatory processes to maintain task performance. In the present study we investigated temporal variability and spatial diffusion of the visual N2 component in a group of high-functioning patients with preserved cognitive performance. 28 patients with schizophrenia and 28 control participants matched for gender, age and education participated in the study. Subjects performed a visual Go/Nogo task, while event-related potentials were obtained. Trial-to-trial latency variability was calculated with a Wavelet-based method. Patients with schizophrenia showed a robust increase in N2 latency variability at electrodes Fz and Cz in all task conditions. Regarding spatial distribution healthy participants showed a focused fronto-central N2 peak. In contrast, patients with schizophrenia showed a more diffuse pattern and additional negative peaks over lateral electrodes in the Nogo condition. These results clearly show that even in high-functioning patients with schizophrenia a higher temporal variability of ERPs can be observed. This provides support for temporal instability of information processing as a fundamental deficit associated with schizophrenia. The more diffuse scalp distribution might reflect processes that compensate for this instability when cognitive control is required.