Repeated exposure to low-level extremely low frequency-modulated microwaves affects cortex-hypothalamus interplay in freely moving rats: EEG study

Abstract

Purpose: To compare the effects of repeated exposure to extremely low frequency-modulated microwaves (ELF-MW) on cortical and hypothalamic electroencephalograms (EEG).

Materials and methods: In 10 freely moving rats with carbon electrodes implanted into the cortex and dorsomedial hypothalamus, averaged frequency spectra (0.5–30 Hz) of the EEG were studied for five consecutive days either under sham exposures (five rats) or under mixed sham/MW-exposures (five rats). The rats were exposed to ELF-MW (915 MHz, 20-ms pulse duration, ∼0.3 mW/cm², 4 Hz) intermittently (1-min ‘On’, 1-min ‘Off’) for 10 min (specific absorption rate, SAR, ∼0.7 mW/g on average) several times per day, with 10-min pre- and post-exposure periods.

Results: In baseline EEG, the activities of 3.2–6.0 Hz and 17.8–30.5 Hz dominated in the cortex and of 6.0–17.8 Hz in the hypothalamus. This cortical-hypothalamic imbalance was relatively stable at sham-exposures and insensitive to ELF-MW in all frequency ranges but one. ELF-MW increased the beta₂ (17.8–30.5 Hz) level in the hypothalamus to a greater extent than in the cortex, causing significant diminishing of the initial EEG bias between them. Moreover, a cumulative phenomenon under repeated exposures to ELF-MW was revealed.

Conclusions: These results are in line with evidence that repeated low-level exposure to ELF-MW affects brain functioning and provide an additional approach when analysing underlying mechanisms.

Keywords:

• frequency spectra
• cortex
• hypothalamus
• ELF-modulated microwaves
• rats

Acknowledgements

We are grateful to Dr Chris Howarth and Mr Adam Ranson for helpful comments and corrections of English in our manuscript. This work was supported by the Ministry of Science and Technological Development, Republic of Serbia (Grant No. 143027).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.