[Electrophysiological evaluation of human consciousness level by "Automated Fluctuation Analysis" of human high frequency EEG].

This study is done to clarify the clinical meaning of "Automated Fluctuation Analysis" of high frequency EEG in man especially focused on the fine alteration of consciousness level of the subjects. Twenty normal volunteers were utilized for this study. They were divided into two groups, the subjects who felt sleepiness (Group S; N = 8) and the subjects who denied it (Group W; N = 12), during the EEG recording. "Automated Fluctuation Analysis" of high frequency EEG had been presented in our previous paper. In short, it is made of three steps, amplification of EEG signal, A/D conversion and Fast Fourier Transform by signal processor and extraction of Lorentzian parameters. Power spectral density (PSD) was displayed on log-log graph. Then the third step is performed by the best curve fitting program to the following equation, S (f) = S1/[1 + (f/fc1)2] + S2/ [1 + (f/fc2)2], where S(f) is power spectral density at any frequency f, S1 and S2 are plateau level of initial and second Lorentz, respectively and fc1 and fc2 are the corner or half power frequency of initial and second Lorentz, respectively. The algorithm of this program to extract these parameters were mathematically based on Brown & Dennis. As results, 1. PSD of human high frequency EEG was composed of double Lorentzians and vanished into white level within 1kHz. 2. A topographical display of S1 value revealed hyperfrontal in group W, which is in accordance with the cerebral blood flow study by Ingvar.(ABSTRACT TRUNCATED AT 250 WORDS)