Unlike the results of the current study, a significant reduction of early auditory gamma total power was observed in a sample of chronic schizophrenia patients, along with significant reductions in phase synchrony (Roach, this issue). Many factors may contribute to this apparent discrepancy between the findings from these two studies from our laboratory, including the fact that total power measurements in the gamma range are hampered by a relatively poor signal-to-noise ratio compared to evoked power measurements. This is due to the inherently greater noise present in single trial EEG epochs relative to the ERP derived by averaging them. However, another possibility is that reduction in the magnitude of early auditory gamma oscillations is a late developing abnormality that is only evident robustly in chronic schizophrenia patients, whereas reduced gamma phase synchrony and associated reductions in evoked gamma power are present early in the illness course, possibly even before illness onset during the prodromal period. While speculative, this hypothesis is consistent with the idea that the mechanisms subserving the phase synchronization of gamma oscillations with respect to an auditory stimulus
