Abstract
Electroencephalogram (EEG) potentially contains much information about the function of the brain.It is however often difficult to get the information in understandable forms without resorting to pertinent analytical methods.The analytical method most frequently used requires 5-second analysis time.This means that any event whose duration is less than 5-second is undetectable.
It has been recently proposed that the analysis time can be made as short as 1.5-second (the sectional analysis).Namely, the data obtained during a period of 1.5-second are divided into 150 equal parts, thus each part corresponding to 1.5/150 second, then each part is added in succession and repeatedly until exactly 5 seconds are reached.Two lines of investigations have been carried out.
First, sectio nal and 5-second analytical methods were applied to the EEGs of the cerebrovascular diseases and the results obtained with these two methods were compared with each other.Secondly, the EEGs of the cerebral arteriosclerosis and the apoplexy were categorizedaccording to the results obtained with the sectional analysis.
The results are as follows: 1 Bi-parietal EEGs in the acute stage of cerbrovascular diseases were analyzed during waking and relaxation by means of the sectional and the 5-second analytical methods.While both methods revealed a higher density in the power spectrum from 1 to 4 Hz on healthy as well as lesioned sides, it was only through the sectional analysis that a small peak corresponding to a-rhythm was distinguished on the healthy side.In the case of the cerebral infarct, both methods disclosed a higher density from 5 to 7 Hz on the lesioned side whereas it was only through the sectional analysis that peaks corresponding to a-rhythm were detectedon both sides.
2 The EEGs of the arteriosclerosis and the apoplexy were analyzed continuously for 40 seconds by the sectional analysis.The patients with cerebral arteriosclerosis exhibited either a normal or higher blood pressure.In the former, the highest density in the power spectrum was observed at 10 Hz while in the latter it was seen at 8 or 9 Hz on both healthy and lesioned sides.In patients with a long-standing hemiparesis, the EEG on the lesioned side remained abnormal.On the other hand, in patients who had almost completely recovered from the paresis, the EEG was similar in pattern to that of the cerebral arteriosclerosis.
Key words: frequency analysis, cerebrovascular dise ases, sectional analytical method, digital data, power spectrum density
