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Schizophrenia Bulletin Advance Access published online on August 6, 2008
Schizophrenia Bulletin, doi:10.1093/schbul/sbn093
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© The Author 2008. Published by Oxford University Press on behalf of the Maryland Psychiatric Research Center. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org.

Event-Related EEG Time-Frequency Analysis: An Overview of Measures and An Analysis of Early Gamma Band Phase Locking in Schizophrenia

Brian J. Roach2 and Daniel H. Mathalon1,3
2 Mental Health Service, Veterans Affairs Medical Center and Northern California Institute for Research and Education, San Francisco, CA
3 University of California at San Francisco, San Francisco, CA

1 To whom correspondence should be addressed; VAMC 116D, 4150 Clement Street, San Francisco, CA 94121; tel: 415-221-4810, fax: 415-750-6622, e-mail: daniel.mathalon{at}ucsf.edu.

An increasing number of schizophrenia studies have been examining electroencephalography (EEG) data using time-frequency analysis, documenting illness-related abnormalities in neuronal oscillations and their synchronization, particularly in the gamma band. In this article, we review common methods of spectral decomposition of EEG, time-frequency analyses, types of measures that separately quantify magnitude and phase information from the EEG, and the influence of parameter choices on the analysis results. We then compare the degree of phase locking (ie, phase-locking factor) of the gamma band (36–50 Hz) response evoked about 50 milliseconds following the presentation of standard tones in 22 healthy controls and 21 medicated patients with schizophrenia. These tones were presented as part of an auditory oddball task performed by subjects while EEG was recorded from their scalps. The results showed prominent gamma band phase locking at frontal electrodes between 20 and 60 milliseconds following tone onset in healthy controls that was significantly reduced in patients with schizophrenia (P = .03). The finding suggests that the early-evoked gamma band response to auditory stimuli is deficiently synchronized in schizophrenia. We discuss the results in terms of pathophysiological mechanisms compromising event-related gamma phase synchrony in schizophrenia and further attempt to reconcile this finding with prior studies that failed to find this effect.

Keywords: time-frequency analysis / EEG / power / phase


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