この研究は、これまでに報告されている、睡眠紡錘波に対するパルス変調高周波電磁界の影響において、20Hz以上の高調波成分が変調成分に含まれていた問題を分析している。そのため、この研究ではばく露信号の高調波成分を十分に減衰させたことを確認して、2Hzでパルス変調した900MHz信号ばく露（SAR = 2 W/ kg）、2Hzのパルス磁界ばく露、擬似ばく露の3つのばく露（睡眠前30分間）を無作為二重ブラインド法により、25人の健常な男性被験者に1週間の間隔で実施した。その結果、両方のばく露後の睡眠脳電図において紡錘波帯スペクトルパワー上昇などが見られたことから、これらの影響は20Hz以上の周波数成分が根本的要因ではないこと；しかし、脳電図反応にばく露の種類による相違があったことから、これらの影響は復調信号のみを基礎とするという復調仮説は支持されなかったこと、などを報告している。
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The aim of the study was to test if a signal without significant harmonics above 20 Hz is sufficient to influence the EEG. In addition (part 2), the authors wanted to investigate whether applying a magnetic field with the same pulse sequence as applied in the pulse modulated radiofrequency exposure would result in similar changes in the EEG.
Part 2 was an attempt to test the demodulation hypothesis, i.e. that the effects are induced by the demodulated radiofrequency signal (corresponding to the low frequency envelope of the transmitted signal) via an electrically non-linear structure inside the human brain. Demodulation occurring in the brain has been proposed as one possible mechanism for the effects of pulse modulated radiofrequency electromagnetic fields.
25 young healthy men were exposed/sham exposed at weekly intervals to three different conditions for 30 min before sleep.
| 周波数 | 900 MHz |
|---|---|
| タイプ |
|
| ばく露時間 | continuous for 30 min |
| Modulation type | pulsed |
|---|---|
| Repetition frequency | 2.08 Hz |
| Additional information |
Pulsed signals had a basic modulation frequency of 2 Hz and a peak-to-average ratio of 4 in pulse amplitude. In order to reduce the higher harmonics the pulse structures were smoothened by applying a Gaussian low-pass filter (-3 dB at 20 Hz), reducing the spectral power above 20 Hz by more than a factor of 10 and by approx. 10 000 at 50 Hz. |
| ばく露の発生源／構造 |
|
|---|---|
| Distance between measurement device and exposed object | 115 mm |
| ばく露装置の詳細 | patch antenna 42 mm vertically above ear canal, 115 mm from left side of head (unilateral exposure) |
| Sham exposure | A sham exposure was conducted. |
| 測定量 | 値 | 種別 | Method | Mass | 備考 |
|---|---|---|---|---|---|
| SAR | 2 W/kg | - | - | - | peak spatial average of head tissue |
| 周波数 | 2 Hz |
|---|---|
| タイプ |
|
| 波形 |
|
| ばく露時間 | continuous for 30 min |
| ばく露の発生源／構造 | |
|---|---|
| ばく露装置の詳細 | rectangular shaped coils (33 x 39 cm, 2 x 23 windings) on each side of the head separated by 25.7 ± 0.5 cm, depending on the participant's anatomy |
| Sham exposure | A sham exposure was conducted. |
Radiofrequency exposure increased EEG power in the spindle frequency range. Furthermore, delta wave and theta wave activity (Non-REM sleep), and alpha wave and delta wave activity (REM sleep) were affected following both exposure conditions. No effect on sleep architecture and no clear impact of exposure on cognition was observed.
These findings demonstrated that both pulse modulated radiofrequency and pulsed magnetic fields affected brain physiology, and the presence of significant frequency components above 20 Hz was not fundamental for these effects to occur. Because responses were not identical for all exposures, the study does not support the hypothesis that effects of radiofrequency exposure are based on demodulation of the signal only.
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