LTE Electromagnetic Fields Exposure Modulates the Resting State EEG on Alpha and Beta Bands.
dinsdag, 03 mei 2016 - Categorie: Onderzoeken
25 april 2016
Clin EEG Neurosci. 2016 Apr 25. pii: 1550059416644887. (Epub ahead of print)
Alpha and Beta Bands.
Yang L1, Chen Q2, Lv B1, Wu T3.
1Bioelectromagnetic Lab, China Academy of Telecommunication Research of Ministry of Industry and Information Technology, Beijing, China.
2Department of Radiology, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
3Bioelectromagnetic Lab, China Academy of Telecommunication Research of Ministry of Industry and Information Technology, Beijing, China email@example.com.
Long-term evolution (LTE) wireless telecommunication systems are widely used globally, which has raised a concern that exposure to electromagnetic fields (EMF) emitted from LTE devices can change human neural function. To date, few studies have been conducted on the effect of exposure to LTE EMF. Here, we evaluated the changes in electroencephalogram (EEG) due to LTE EMF exposure. An LTE EMF exposure system with a stable power emission, which was equivalent to the maximum emission from an LTE mobile phone, was used to radiate the subjects. Numerical simulations were conducted to ensure that the specific absorption rate in the subject's head was below the safety limits. Exposure to LTE EMF reduced the spectral power and the interhemispheric coherence in the alpha and beta bands of the frontal and temporal brain regions. No significant change was observed in the spectral power and the inter-hemispheric coherence in different timeslots during and after the exposure. These findings also corroborated those of our previous study using functional magnetic resonant imaging.
© EEG and Clinical Neuroscience Society (ECNS) 2016.
EEG; electromagnetic field exposure; functional magnetic resonance imaging; long-term evolution; resting state; specific absorption rate
''.. the results of resting state EEG experiments have been contradictory. For example, some studies have reported enhancement of the alpha (8-12 Hz) and beta (13-30 Hz) band power values after exposure to pulse-modulated 450- and 900-MHz signals,6,7 pulse-modulated magnetic fields,8 and active mobile phone signals.9,10 In contrast, some studies have shown decreased alpha band activity after 20 minutes of extremely low-frequency EMF exposure,11,12 or 5 minutes of magnetic field exposure,13 or global system for mobile communications (GSM) EMF exposure.14 Many studies also found no changes in the EEG after either modulated or unmodulated EMF exposure.15-17 These inconsistencies could be attributed not only to the differences in the signal type, the modulation, the exposure frequency, the exposure intensity individual anatomy, the ages of the subjects, and the exposure duration16,18-20 but also to the lack of rigorous experimental designs. Most of the previously published studies have focused on GSM,3 WiFi,21 and Universal Mobile Telecommunications System (UMTS),10 signals. An emerging technology, “longterm evolution” (LTE) wireless service, has been deployed since 2009 and the number of global LTE subscribers is expected to reach 1.37 billion by the end of 2015.22 Other than our previous functional magnetic resonance imaging (fMRI) study,23 there are very few reports on the effect of exposure to LTE EMF on brain function. We previously found that 30 minutes of exposure to LTE EMF modulated the spontaneous low-frequency fluctuations.23 We were interested in confirming our previous results using another neurophysiological method and also sought to assess the evolution of the effect over time during such exposure. In this article, we have investigated for the first time the changes in the resting state EEG caused by exposure to LTE signals. The exposure dose was below the current safety limit. In order to assess brain activities on different levels, we evaluated spectral power and interhemispheric coherence, which allowed investigation of EEG changes in specific brain regions, as well as their correlations, at different time points. We show that exposure to LTE EMF decreased the alpha and beta band power spectrum and interhemisphere coherence.''
''The age of the subjects was 30.2 ± 2.7 years.''
''A plastic spacer of 1 cm was used to maintain the distance between the right ear and a standard dipole. We applied 2 power meters (E4416A, Keysight, Santa Clara, CA, USA) to ensure a constant incident power to the emission dipole.25 The power delivered to the dipole was 24 dBm (peak value), equivalent to a theoretical maximum emission by an LTE terminal.''
''All 25 subjects participated in the double-blind and counterbalanced experiment.''
''The experiment included 2 sessions, which were separated by 1 week. Each session lasted 50 minutes and comprised 5 time slots. We indicated each time slot (10 minutes) in a session as sub1 to sub5. The radiation dipole was power off for the first (preexposure, sub1) and the last 10 minutes (postexposure, sub5) timeslots. Subjects were exposed to real EMF exposure in the 3 time slots (sub2 to sub4) between the first and the last 10 minutes in only 1 of the 2 sessions. The order of the 2 sessions was randomly selected per subject. The subjects were not informed of the sequence of each session; however, they were aware of the possibility of being exposed. On the other hand, the staff who analyzed the data did not know the sources of the EEG traces.''
''The simulations yielded 1.34 W/kg (pSAR10g) and 1.96 W/kg (pSAR1g), with the electrodes, and 1.27 W/kg (pSAR10g) and 1.78 W/kg (pSAR1g), without the electrodes (Figure 2) when the dipole emitted radiation. Therefore, the presence of the EEG electrodes increased pSAR10g and pSAR1g by about 5.5% and 10.1%, respectively. Accordingly, the maximum resultant temperature increase was no more than 0.1°C ....''
''Previous studies on GSM and UMTS signal exposure frequently reported changes in interhemispheric coherence18,20 and the spectral power12 in the alpha band in the frontal and temporal regions, which were also confirmed by our results on LTE EMF exposure. Moreover, modulation of the power spectrum in the beta band, including both an increase and a decrease, was reported.10,38 Several reasons may account for the inconsistency. First, the signal frequency and its modulation influenced the affected EEG band: for example, exposure to 2G signals affect the alpha rhythms, whilst exposure to 3G signals do not.10,19 In contrast, the modulated 450-MHz signals of various intensities can change beta activity much more markedly than alpha band power.39 Second, gender and the individual sensitivity38,40 may influence the effect on different bands. Hence, we attempted to reduce the variability by enrolling the subjects with the same gender and age.''
''In particular, power spectral analysis has shown significant differences in the left frontal brain regions, that is, the remote side, on exposure. This may be associated with modulation of neural activity in the remote/contralateral brain regions. The remote effects of EMF have been observed in many previous studies.2,9,41,42 Our results reconfirmed that the effects were also seen with LTE EMF exposure.''
''The power spectrum and the interhemispheric coherence did not differ significantly over sub2 to sub5. Thus, the observed effect did not change with the exposure time and the effect was therefore not developing. The reduction in alpha band activity has been associated with a decrease in individual information-processing ability, alertness, and cognitive performance. 16,43-48 The decrease in beta band activity could be interpreted as decreased alertness, arousal, and excitement 49 or a low level of fatigue. 50 Notably, EEG power fluctuation was not in one-one correspondence with the change in behavioral/cognitive performance which should be evaluated by specifically designed experiments as the report by Haarala et al.51 No conclusion could be obtained by our study that the present EMF exposure affected the subjects’ cognitive abilities.''
''This work studied EEG changes caused by LTE EMF exposure. An exposure system with a fixed power incident to a radiation dipole was used; this simulation demonstrated that the SAR was within the safety limits. LTE EMF exposure modulated the EEG in the alpha and beta bands at the frontal region of the near and remote sides, and at the temporal region on the near side. No developing effect was found in the periods during and after the exposure. Our results agreed to some extent with those of our previous fMRI study on LTE exposure. Our finding indicated that the LTE EMF exposure with the intensity beneath the safety limits could modulate the brain activities.''
''Future studies should focus on the correlation of EEG changes with spatial SAR distribution. By taking individual anatomical structure into consideration, a precise dose-effect relationship can be established. EEG changes with a finer temporal resolution during the exposure session should also be evaluated.''
Prior LTE study
23. Lv B, Chen Z, Wu T, et al. The alteration of spontaneous low frequency oscillations caused by acute electromagnetic fields exposure. Clin Neurophysiol. 2014;125:277-286. 1.usa.gov/1gTqxVr .
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