EEG coherence and topography in superquiescent state

Author: Zhou Bomin//He Zhongji
Zhejiang University, Zhejiang Province, China [1]
Conference/Journal: 1st World Conf Acad Exch Med Qigong
Date published: 1988
Other: Pages: 39 , Word Count: 838

The superquiescent state is a special physiological state. Chinese qigong, Indian Yoga and transcendental meditation can all completely free a person from external and internal disturbances, bring about protective inhibition of the activity of the cerebral cortex, and make a person enter the superquiescent state.

The quiescence index is an objective measurement of the degree of quiescence. One of the important features of the superquiescent state is the synchronism of EEG in all regions, so we used EEG coherence which reflected the synchronous degree of two signals as one item of the quiescence index, and defined the coherence index as the number of times the coherence peaks above the 0.95 threshold during a 2.5 min. period. EEG topography is an important tool in clinical neurophysiology. In order to study the space appearance of EEG in the superquiescent state. EEG power topography and EEG coherence topography were developed. Two signals in EEG coherence analysis were derived from F3, F I (International 10-20 system) with Cz used as ground. The derivations were dipolar and referenced to linked Al. In EEG topography recordings from Fpl, Fp2, T3, C3, C I, T4, OL and 02, the derivations were monopolar and reference to linked Al. EEG signals were digitized on-line to 8 bits at 60 samples per sec per channel. A power spectrum was obtained by Fast Fourier transformed with 128 data points. A cosine slope window was added to decrease spectral leak. Coherence was computed for each 1.12 esc. epoch of data using the average of 12 overlapping frames of 128 samples, each increment with 12 samples between frames. The EEG index in power topography analysis was the spectrum of each EEG band (there were 6 bands as well as delta, theta, alpha-l. alpha-2, beta-l, beta-2), or the total EEG spectrum. In EEG coherence topography the value of the Fpl derivation was the EEG coherence index between signals from Fpl and Fp2. The value of other recording derivations were the EEG coherence index between signals from those areas and Fpl. Linear interpolation was used in topography analysis. The value of any point was the EEG index weighted average of the three recording derivations which were closest to that point. The weight factor was inversely proportional to the distance between two points. There were 1960 display units which consisted of a pararound area in topography. A topography map was produced by a printer, with 11 homogeneous gray degrees which were expressed by density of the printed unit. With an APPLE-II microcomputer an on-line analysis program with 6502 assemble language and BASIC was accomplished.

In our experiment, the EEG of the subjects was individually measured according to these protocol: 5 min. of quite sitting, 30 min. of the qigong exercise and 5 min. of quite sitting again. The meditator was asked to close eyes in all processes. Communication to the subject was via an intercom at a low volume. Eight channels of ND-82B polygraph were used for primary amplification and paper chart recording. Before the signals were digitized the polygraph outputs were reamplified by an eight channel amplifier with 6 dB settings at 40.8 Hz.

After 34 experiments, the following was found:

1. The control group (14 males with a mean age of 25) after 30 min. of quiet sitting, the frontal EEG coherence index had no significant increment. The EEG power topography and EEG coherence topography also had no outstanding changes. The EEG power was mainly in the occipital region with a dominant frequency in band alpha-2.

2. Exercisers with short-term training (12 males, 3 females with a mean age of 14 and the period of practice 2-48 months): After meditating for 5 min. the frontal EEG coherence index showed a little increment though it did not reach the significant level, but there was a marked increment after 30 min. (P<O.01) . In the EEG coherence topography, the index value of the frontal and occipital region showed an increment with no notable change in other regions, The EEG power distribution in band alpha-l had changed, and there was a power shift from the occipital to the frontal lobe.

3. Exercisers with long-term training (5 males with a mean age of 52 and over 48 months of practice): The frontal EEG coherence index increased greatly after meditation (P< 0.005) . There was no difference in EEG coherence topography before meditating compared with the matched controls. But after beginning to meditate the coherence index increased in all regions. The increase was more obvious in the left hemisphere 10 min. Iater, whereas there was a stead(y) increment with greater amplitude in the right 30 min. Iater. It indicated that the connection between the two cerebral hemispheres was enhanced in the later period of training. In the EEG power topography, the EEG power rose sharply and the dominant region was shifted from the occipital to the left frontal region and the right temple with a dominant frequency decrement from band alpha-l to theta.
From the above mentioned analysis, we believe that the following factors must be considered when discussing the quiescence index:

(l) The EEG coherence in all regions; (2) the increment of the EEG spectrum in all regions; (3) the decrement of the dominant frequency; (4) the shift of the dominant EEG region.