Measurements by biphasic changes of the alpha band amplitude as indicators of arousal level

The objective of this study was to develop a method of measuring arousal level by examining the change rates with activation of the alpha band amplitude using the concept of the inverted U-shaped pattern of transition of this amplitude. We investigated change rates by inspecting the electroencephalogram, and we evaluated their correlations with a criterion index of the arousal level (a reaction time measure), and other relevant basic parameters in 14 normal volunteers. In order to confirm that alpha band amplitude change followed an inverted U-shaped curve, we examined the transition of that index in a resting-and-relaxing condition. In the third session, the change rates upon stimulation and after resting had positive and negative correlations, respectively, with the reaction time measure, verifying that they are 'negative' and 'positive' arousal level indices. Further examinations were conducted for the third session. The change rates upon stimulation and after resting had negative correlations with each other. Neither of them had a significant correlation with the alpha band amplitude. Neither alpha band frequency, alpha band amplitude, or theta band amplitude, all of which are regarded as indices for intra-subject arousal level transition, had any significant correlation with the reaction time measure. These results revealed that the change rates of the alpha band amplitude are better indices for inter-individual arousal level variation than other conventional indices.