To study the patterns of activation of the P600 waveform of the event-related potentials (EEG) during a working memory task (digit span test) and whether these patterns are radiofrequency exposure and gender dependent.
The P600 component is related to linguistic processes and working memory.
Two different groups took part in two separate experiments. The first group consisted of 19 healthy subjects (9 men and 10 women). In the second experiment 20 individuals participated (10 men, 10 women). One group was exposed to 900 MHz signal and the other group to 1800 MHz. The subjects performed the memory test (digit span test) 52 times and the duration of one recording was about 45 minutes. Each subject performed the test twice (with and without exposure). Each task started with a warning stimulus signal tone of either low (500 Hz) or high frequency (3000 Hz). At the end of the number sequence presentation, the same tone was repeated and the subjects had to recall the numbers in the same (500 Hz) or in the opposite order (3000 Hz tone).
| Frequency | 900 MHz |
|---|---|
| Type | |
| Exposure duration | about 45 min. |
| Exposure source | |
|---|---|
| Distance between exposed object and exposure source | 20 cm |
| Chamber | tests performed in a Faraday room |
| Setup | dipole antenna fixed near the volunteer's right ear; warning signal and auditory tasks were presented via a non-metallic earphone |
| Sham exposure | A sham exposure was conducted. |
| Frequency | 1,800 MHz |
|---|---|
| Type | |
| Exposure duration | about 45 min. |
| Exposure source |
|
|---|---|
| Sham exposure | A sham exposure was conducted. |
Both principal component analysis and analysis of variance produced congruent results, showing that activation of the P600 component occurs early and more intensely in the region of the posterior EEG electrodes and in a less intense manner in the central electrodes. Conversely, the activation at the anterior electrodes arises later with a considerably reduced intensity.
In the absence of the radiofrequency electromagnetic field female subjects exhibited significantly lower amplitudes at anterior electrodes and earlier latencies at central electrodes than male subjects. These differences disappear under radiofrequency exposure. Thus, the P600 component follows distinct patterns of activation in the anterior, central and posterior brain areas and gender differences are observed simultaneously at several electrodes within these areas.
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