Left Temporal Lobe Dysfunction in Schizophrenia: Event-Related Potential and Behavioral Evidence From Phonetic and Tonal Dichotic Listening Tasks
Gerard Bruder, PhD; Jürgen Kayser, PhD; Craig Tenke, PhD; Xavier Amador, PhD; Michelle Friedman, BA; Zafar Sharif, MD; Jack Gorman, MD
Background:
Asymmetric reduction of the P3 event-related potential (ERP) has provided evidence of left tem-poral lobe dysfunction in schizophrenia. Prior studies have been limited by reliance on simple target detection (odd-ball) tasks with pure tones. This study investigated the time course and topography of ERPs to binaural syl-lables or complex tones in dichotic listening tasks.
Methods:
Event-related potentials of 26 patients meeting criteria for schizophrenia (n = 19) or schizoaffective disorder (n = 7) and 26 healthy controls were recorded from 30 scalp electrodes during 2 dichotic tasks in which different syllables or complex tones were simulta-neously presented to each ear. A principal components analysis was used to derive factor scores corresponding to overlapping components in ERP waveformsÃN1, N2, P3, and a late-positive potential.
Results:
Healthy controls showed a right ear advantage for perceiving dichotic syllables, which was associated with greater N2 amplitude at left than right temporopa-rietal sites. Patients with schizophrenia did not show ei-ther this perceptual or N2 asymmetry. Patients also had smaller late-positive potential amplitude when com-pared with controls for both syllables and complex tones, with greatest decrement over left temporal sites.
Conclusions:
A right ear advantage in healthy adults for perceiving consonant-vowels was associated with a left-lateralized ERP component peaking at 200 milliseconds after syllable onset (N2). Patients with schizophrenia failed to show either of these task-dependent asymmetries, which may indicate a dysfunction of left temporal re-gions involved in phonetic classification. A task-independent asymmetric reduction of a later positive po-tential in patients with schizophrenia resembled left temporal P3 reductions reported for auditory oddball tasks.