Abstract
The fine structure of the frequency spectrum of the EEG of both resting condition and photic stimuli application led from the occiputs of healthy adults was analysed by120ordinates multi-harmonic analysis (time for analysis-approximately2sec. Resolving power for frequency-approximately0.5c/s.), and the following result was obtained:
(1) What may be regarded as line spectrum was not found in the EEG frequency spectrum. In most cases, on each band of delta, theta and alpha waves, a certain number of peaks were seen. No outstanding peak was detectable among the beta waves. Not a few cases were suggestive of the fact that the band of alpha waves should be extended to 9-14c/s. or 7-15c/s. instead of limiting it to8-12or13c/s.
(2) It has hitherto been considered that photic stimuli cause alpha waves to diminish and beta waves to appear, but though the alpha wave peaks of low frequency do diminish with moderate stimulating effect, those of high frequency grow larger or new peaks appear. Contrary to what has hitherto been believed, beta waves diminish under photic stimuli.
When the stimulating effect is great, all the alpha wave peaks diminish; a part of the beta wave peaks temporarily rises while the other part diminishes.
(3) Although delta waves show no definite type of change under the photic stimuli, theta waves tend to diminish.
(4) When the stimulation lasts longer, a certain number of alpha waves begin occasionally to appear in group on the EEG tracing. The frequency spectrum in this part shows not only the recovery of the peaks corresponding to the principal peaks immediately preceding the stimuli application, but also the remaining peaks of higher frequency. Those of low frequency also tend to appear.
(5) From the above result it was found that some waves in alpha wave band show the reaction contrary to each other to photic stimuli, suggesting that some waves involve different physiological significance.
