A.V.Kramarenko

THE COMPARISON OF LOCAL CHANGES IN
EEG TO THE MAP OF A CELLULAR PHONE'S FIELD


The influence of GSM phone on electroencephalogram is still at the stage of study [1-3]. Significantly, it is caused by difficulties and inability to record a clear EEG during usage of this type of telephone by the patient. Therefore for evaluation of such influence data that was received either using the unmodulated signal generator or by the researching residual effects after turning of cellular phone are used very often. The both of this approaches do not describe the real influence of modulated high frequency signal in EEG in real time and that is why they can be used only for initial estimation of such influence.

It should be also taken into account that cellular phone do not provide continuous radiation, but transmits the information partially (in frames), which means that between frames the transmitter works with zero power. The frequency off/on of the transmitter is approximately equal to 217 Hz. The carrier frequency is close to 900 or 1800MHz. Under influence of such signal electric currents changing from 0 to maximum values with the period of datum portion change approximately during 5 msec occur in the electrolytes. It is equal to an effect of amplitude-modulated signal with 100% modulation depth, unlike usual radiophone, in which narrow-band frequency modulation is used and where these effects are absent.

The current in conducting medium of isotonic NaCl solution can be easily registered using the low-frequency oscillograph (Fig.1).

Fig.1 Snapshot from oscillograph C1-83 screen, scanning 2mV/point, 2 msec/point. Ericsson A1018S 900 MHz phone. NaCl solution. AgCl weak-polarized EEG electrodes. Proper observation.

The map of the field generated by a cellular phone is shown in Fig.2.

Fig.2. Mobile phone's electromagnetic field map synthesized by "CST Microwave Studio" program (published by authority of "ElectronTrade" company, Russia).

Pay attention to the very complicated spatial distribution of a signal, and its locking in the mediums of maximum conduction. It means, that the biggest physiological effect will be strongly pronounced in the places of the largest area of contact with liquor. And the locking of the field through the area of ipsilateral eyeball makes us suggest that the influence on the basal surface of the brain might be even more than on the areas directly adjoining with the antenna. Besides that, all areas with intensive liquor dynamics become (according to this scheme) the places with possible significant local gradient appearance.

Naturally, the changes in EEG will be the most interesting precisely during the presence of this field rather then after its turning off. But to register an EEG signal during a cellular phone operation is a difficult engineering task. Usual electroencephalograph can not function with the presence of such noise (see Fig.3), and the further trials of signal filtration are doomed to failure (detailed research does not merge with this publication).

Nevertheless the solution exists, and blameless registration off EEG in such conditions is possible. Analyzing the first seconds of record, the observable changes absence amazes. The depression of alpha activity and all prescribed test irritants responses are registered as well. Moreover, the frequency of the main rhythm retains with a high preciseness and the signal spectrum changes slightly. And if to rate an EEG by each channel separately, it can be discovered just some reliable increase in median frequency of spectrum which coincides with the findings of other experiments [4]. Additionally, single sharp waves are registered in the areas close to the antenna.

Fig.3. The noise in EEG when turning on the cellular phone. The patient's eyes are closed. The observation of electrophysiological laboratory of Central Clinical Hospital N5 (Kharkov, Ukraine).
Fig.4. The EEG of a healthy patient. The patient's eyes are closed. Moment of turning the cellular phone on is marked with an arrow. The registration is done on the ExpertTM EEG system, made by the TREDEX Company Ltd. (Kharkov, Ukraine).


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