Time-frequency analysis of the beta band on an electroencephalogram

Abstract

  In the study of brain function, several recording methods are employed. The advantage of an electroencephalogram (EEG) is its high temporal resolution. Time-frequency analysis of EEG data can provide activity changes in the frequency band of millisecond-order. Beta band activity is believed to reflect information processing in the cortico-cortical connection. Therefore, we studied beta band changes in cortical oscillatory activity in the cerebral cortex in order to investigate changes in decision-making and inhibition during a visual oddball task. Eleven right-handed healthy subjects participated in this study. In the oddball task, the subjects were required to press a button when the target stimulus (go condition, 20% probability) was presented, whereas they were required to withhold their response when the standard stimulus (no-go condition) was presented. EEG data were recorded from the scalp using 128 channels. The data were analyzed by time-frequency analysis for each go and no-go condition. In both conditions, an increase in the beta band activity of approximately 15 Hz was observed in the frontal association area, beginning after stimulation, and this increase was observed in the left motor association area. The duration was clearly shorter in the no-go condition than that in the go condition. These results suggest that an increased beta band activity in the frontal association area may represent integrative processing of visual information and decision-making in both conditions, whereas it indicates inhibition in the no-go condition. Moreover, the shorter beta band activity in the motor association area during the no-go condition indicates increased GABA-mediated inhibition.