13 subject participated.
Each subject went through two (or four?) EEG recording sessions on different days, double-blind and randomly assigned to real and sham exposure. Both exposure and sham protocols were applied twice to each subject. Microwave exposure was identical to previous studies [Lass et al., 2002 and Hinrikus et al., 2004], but three different modulation frequencies were applied.
|Distance between exposed object and exposure source||10 cm|
|Chamber||During the EEG recording session, lasting 40 min, subjects were lying in a relaxed position, with eyes closed and ears blocked, in a dark room. The experimenter was also in the room.|
|Setup||The antenna was located 10 cm from the skin on the left side of the head.|
|Sham exposure||A sham exposure was conducted.|
|Additional info||10 minutes of reference recordings were followed by three times 10 min of exposure at a constant modulation frequency of 7, 14, or 21 Hz. The succession of the modulation frequencies was randomly assigned by a computer program.|
The data support the authors' hypothesis that the effect of modulated microwaves on the EEG differs at different modulation frequencies. The microwave irradiation modulated at 14 and 21 Hz enhanced the EEG power in the alpha wave and beta wave frequencies whereas no enhancement of the EEG power was found during exposure at the modulation frequency of 7 Hz. Thus, it can be suggested that the effect of an external stimulus on brain oscillations is stronger if the frequency of the stimulus is higher or close to the physiological frequency of brain rhythms. The changes were more obvious at the beginning of the exposure segments. No changes in the EEG theta wave power were detected for any modulation frequencies.
Differences were also found in individual sensitivity to exposure.
The mechanisms of the observed effects of pulse modulated microwaves are unknown.