Author: Gu Younian//Chen Zengkai//Chen Zhaoxi
Affiliation: Dept Physiology, First Medical Colege of PLA, Guangzhou, China [1]
Conference/Journal: 3rd Nat Acad Conf on Qigong Science
Date published: 1990
Other:
Pages: 16 , Word Count: 419
This system is composed of hardwares and softwares. It can sample and process 8-channel EEG signals simultaneously and can give power spectrum histogram of each channel, the wave count of delta, theta, alpha and beta waves. It also can show synchronization of alpha waves between those channels. It is, therefore, convenient for the use in qigong research on human EEG changes before and after qigong and is much better than the processing systems found in the market which can treat 2-channel EEG signals only. This system can be also used in EEG clinic.
The output of EEG, after being amplified by an 8-channel isolated amplifier, is converted into digital signals via a specially designed A/D convertor and is then collected and processed by an Apple II computer.
The software of this system is written by BASIC language and 6502 assembly language including the main control program and the following subroutine programs: data sampling, digital filter, FFT transform, wave count, alpha wave synchronization distinguishing and the final result output and print subroutine program.
Sampling of EEG signals is divided into 3 sections and the total sampling time is 24 seconds. The sampled signals are saved in the disk for use after digital filtering for which a 3 points smooth weighted digital filter is adapted based on the following calculation:
Y(n) = [X(n-1)+2X(n)+X(n+1)]/4
where Y(n) is the output value after filtering, X(n-1), X(n), and X(n+1) are the original sampling value.
The power spectrum is the reaction of the power of each frequency component of EEG, is calculated as ('G sub xx ' is used to represent the second partial derivative of G with respect to x):
G sub xx (f) = S sub x (f) * S sub x (f)
Where G sub xx (f) is the power spectrum, S sub x (f) is the Fourier transform of EEG function of the x-channel, S sub x (f) is the conjugate function of S sub x (f).
The synchronization of alpha wave shows the count of occurrence of the alpha waves in all the 8 channels appearing simultaneously and with the same wave length. For convenience, the 1st and 2nd channels are used as the reference channels and the mutual alpha waves in the other 6 channels are determined.
The wave count of delta, theta, alpha and beta waves in all the 8 channels is calculated by counting the wave length of different ranges. The wave length is the time difference between two minimal points which is obtained by differential calculus.