Frequency analysis in routine electroencephalography.

Abstract 1. 1. The purpose of this study was to develop an automatic method which could partially substitute for the visual evaluation of EEG background activity. An important indicator was presumed to be the quantity of theta activity (in an awake adult). The great variation of frequency analysis output data does not, however, allow its direct use. 2. 2. It was found that the magnitude of the ratio “theta/alpha”, especially after empirically determined correction, is comparable to the visual estimation of the amount of theta activity. The higher the proposed indicator, the higher the probability that the EEG record will be visually judged as non-normal. The correction is applied by adding the value “30” (if the length of epochs is 15 sec) to the quantity of alpha activity expressed in μVsec. 3. 3. The proposed method could be employed in routine electroencephalography as a supplement to the usual evaluation of background activity. In some special cases (the consideration of focal changes, fast screening of a large number of patients, etc.) it could be applied almost independently. For this purpose an analogue instrument was built which automatically indicates the result of measurement. It is hoped that a simple broad-band frequency analysis may in this way become a useful tool for routine EEG examination.