Peak gamma latency correlated with reaction time in a conventional oddball paradigm

Objective: To determine whether a relationship existed across trials between evoked gamma and reaction time in a conventional cognitive ERP paradigm. Methods: Auditory oddball data in 40 normal subjects was examined. A moving Welch window and short time FFT were employed to elucidate the time course of gamma (29 to 45 Hz) activity in each single-trial target ERP. The time point with maximum total gamma amplitude (across all sites) was identified automatically, and the associated amplitude, power and latency of this peak was determined. Spearmanʹs rank correlation was employed to examine the relationship of these measures with reaction time. Results: A highly significant and robust correlation between peak gamma latency and reaction time was found (P=0.000001). Further frequency analysis revealed that this relationship was primarily confined to the 37 to 41 Hz band. This narrow band finding, coupled with the fact that the finding remained after exclusion of possibly EMG contaminated epochs, indicated that the effect was not due to EMG contamination. No relationship between peak gamma amplitude or power and reaction time was found. Conclusions: Peak evoked gamma latency was correlated with reaction time and seems likely to have functional significance in relation to stimulus processing.