ERP generator patterns in schizophrenia during tonal and phonetic oddball tasks: effects of response hand and silent count

Jürgen Kayser^1,2, Craig E. Tenke^1,2, Roberto Gil¹, Gerard E. Bruder^1,2

¹Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, NY, USA; ²Division of Cognitive Neuroscience, New York State Psychiatric Institute, New York, NY, USA

Received 25 March 2010; accepted 11 June 2010; published 18 October 2010.

Abstract

Greater left than right reductions of P3 amplitude in schizophrenia during auditory oddball tasks have been interpreted as evidence of left-lateralized dysfunction. However, the contributions of methodological factors (response mode, stimulus properties, recording reference), which affect event-related potential (ERP) topographies, remain unclear. We recorded 31-channel ERPs from 23 schizophrenia patients and 23 age- and gender-matched healthy controls (all right-handed) during tonal and phonetic oddball tasks, varying response mode (left press, right press, silent count) within subjects. Performance accuracy was high in both groups but patients were slower. ERP generator patterns were summarized by temporal PCA (unrestricted Varimax) from reference-free current source density (CSD; spherical spline Laplacians) waveforms, which sharpen scalp topographies. Both patients and controls showed asymmetric frontolateral and parietotemporal N2 sinks peaking at 240 ms and asymmetric parietal P3 sources (355 ms) for targets (tonal R > L, phonetic L > R), but frontocentral N2 sinks and parietal P3 sources were bilaterally reduced in patients. A response-related midfrontal sink and accompanying centroparietal source (560 ms) were highly comparable across groups. However, a superimposed left temporal source was larger for silent count compared to button press, and this difference was smaller in patients. In both groups, left or right press produced opposite, region-specific asymmetries originating from central sites, modulating the N2/P3 complex. The results suggest bilaterally reduced neural generators of N2 and P3 in schizophrenia during auditory oddball tasks, but both groups showed comparable topographic effects of task and response mode. However, additional working memory demands during silent count may partially overlap in time the generation of the N2/P3 complex and differentially affect the asymmetry of P3 subcomponents, particularly when employing conventional ERP measures.

Key Words: schizophrenia; event-related potentials (ERP); P300 asymmetry; surrent source density (CSD); principal components analysis (PCA); tonal/phonetic oddball tasks; N2/P3 complex; silent count; button press