Program No. 934.8. 2003 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience.
Presented at the 33rd Annual Meeting of the Society for Neuroscience, November 8-12, 2003, New Orleans, LA.
Event-Related Potentials (ERPs) of Healthy Adults and Depressed Patients During Dichotic Tonal and Phonetic Oddball Tasks
C.E. Tenke, J. Kayser, S. Shankman, C.B. Griggs, P. Leite, G.E. Bruder
Department of Biopsychology, New York State Psychiatric Institute, New York, NY 10032, USA
Abstract
ERPs (30-channel; 200 sps; blink correction) were recorded from 19 healthy adults and 16 depressed patients (all right-handed) in an oddball paradigm that exploits the perceptual challenge of dichotic stimulation. Stimuli were selected from dichotic tasks known to produce right (consonant-vowel syllables) and left (complex tones) ear advantages in healthy adults. For the tonal task, nontarget stimuli were tone pairs (G and B above middle C), presented simultaneously to each ear (L/R) in an alternating series (L-G/R-B or L-B/R-G), with a constant 2-s SOA. A target tone (A) replaced one of the pair (e.g., L-A/R-B) on 20% of the trials. Subjects responded with a button press to targets (hand counterbalanced within subjects). For the phonetic task, stimuli were spoken phonemes, edited to match the duration and loudness of the tones. Paired nontarget syllables were unvoiced (/ba/, /da/), and the target syllable was voiced (/ta/). Controls performed well in both tasks (mean hit rate 95%), but patients performed poorer for tones (89%) than syllables (98%). ERPs and their surface Laplacians were simplified and compared using unrestricted, covariance-based Principal Components Varimax Analysis. In addition to typical early components (N1, P2), ERPs to nontargets showed a prominent N2, and a late positivity, which was smaller in patients and corresponded to maximum current sources over temporal and lateral parietal sites. For targets, a late positive complex was represented by 4 factors (78% variance), with 2 factors peaking at 300 and 425 ms being less positive in patients than controls. This reduction was most prominent for the early 300 ms peak, particularly for tones. ERP differences between depressed patients and controls were more pronounced than those seen for binaural oddball tasks, probably reflecting the greater task demands.
Support Contributed By: MH36295 and MH50715
Keywords: P300, Principal Components, surface Laplacian, current source density