Hemispatial PCA dissociates temporal from parietal ERP generator patterns: CSD components in healthy adults and depressed patients during a dichotic oddball task
Craig E. Tenkea,b, Jürgen Kaysera,b, Stewart A. Shankmanc, Carlye B. Griggsa, Paul Leitea, Jonathan W. Stewartb,d, Gerard E. Brudera,b
aDivision of Cognitive Neuroscience, New York State Psychiatric Institute, New York, USA; bDepartment of Psychiatry, College of Physicians and Surgeons of Columbia University, USA; cDepartments of Psychology and Psychiatry, University of Illinois at Chicago, Chicago, IL, USA; dDepression Evaluation Service, New York State Psychiatric Institute, New York, NY, USA
Received 16 November 2006; revised 15 August 2007; accepted 10 September 2007. Available online 26 September 2007.
Abstract
Event-related potentials (31-channel ERPs) were recorded from 38 depressed, unmedicated outpatients and 26 healthy adults (all right-handed) in tonal and phonetic oddball tasks developed to exploit the perceptual challenge of a dichotic stimulation. Tonal nontargets were pairs of complex tones (corresponding to musical notes G and B above middle C) presented simultaneously to each ear (L/R) in an alternating series (G/B or B/G; 2-s fixed SOA). A target tone (note A) replaced one of the pair on 20% of the trials (A/B, G/A, B/A, A/G). Phonetic nontargets were L/R pairs of syllables (/ba/, /da/) with a short voice onset time (VOT), and targets contained a syllable (/ta/) with a long VOT. Subjects responded with a left or right button press to targets (counterbalanced across blocks). Target detection was poorer in patients than controls and for tones than syllables. Reference-free current source densities (CSDs; spherical spline Laplacian) derived from ERP waveforms were simplified and measured using temporal, covariance-based PCA followed by unrestricted Varimax rotation. Target-related N2 sinks and mid-parietal P3 sources were represented by CSD factors peaking at 245 and 440 ms. The P3 source topography included a secondary, left-lateralized temporal lobe maximum for both targets and nontargets. However, a subsequent hemispheric spatiotemporal PCA disentangled temporal lobe N1 and P3 sources as distinct factors. P3 sources were reduced in patients compared with controls, even after using performance as a covariate. Results are consistent with prior reports of P3 reduction in depression and implicate distinct parietal and temporal generators of P3 when using a dichotic oddball paradigm.
Key Words: Event-related potential (ERP); Principal components analysis (PCA); Current source density (CSD); surface Laplacian; Oddball task; Dichotic listening; P300; Depression