Evoked γ oscillations in human scalp EEG are test-retest reliable

Objective: Evoked, phase-locked gamma, oscillations of the electroencephalogram (EEG) have been demonstrated to be modulated by both bottom-up as well as top-down factors. However, to date the test-retest reliability of these oscillations has not been studied systematically. Methods: We recorded EEG activity of 12 healthy volunteers in response to stimuli of different sizes. Each participant took part in two sessions separated by two weeks in time. To obtain an estimate of the reliability of evoked gamma band responses (GBRs), we compared frequency and magnitude of phase-locked EEG oscillations between sessions. Results: In response to large stimuli magnitude and frequency of the evoked GBR yielded significant reliability. However, this was not the case for Stimuli which were too small to evoke detectable GBRs. Conclusion: The results are in accordance with studies demonstrating a dependence of gamma oscillations on stimulus parameters. Significance: The current findings Suggest that using appropriate stimulation, the evoked gamma response has sufficient test-retest reliability for use in assessing clinical changes in neurophysiological status. (c) 2006 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.