Effects of Mobile Electromagnetic Exposure on Brain Oscillations and Cortical Excitability: Scoping Review.

Mobile phones have become an integral part of everyday life. With each new generation of mobile technology, transmission power and frequency ranges increase, extending into the millimeter wave spectrum (> 26 GHz). In this context, the question of whether and how mobile phone radiation influences brain function becomes increasingly important. This scoping review summarizes the current state of research on the effects of mobile phone exposure on brain oscillations (EEG) and cortical excitability (TMS) in healthy adults. Unlike a systematic review, no quantitative synthesis or meta-analysis was performed.

The authors searched four databases – MEDLINE, PubMed, Web of Science and Scopus – for primary studies in English on healthy adult humans. They excluded studies with animal models, patient cohorts, or studies lacking quantitative EEG or TMS endpoints. Exposure parameters were characterized by carrier frequency (0.45–3.5 GHz), transmission power or SAR, exposure duration (1 min to 8 h), study design (blinding, crossover), and experimental details (e.g. eyes open vs. closed). The outcomes of interest were EEG band amplitudes and connectivity, and corticospinal and corticocortical excitability, as assessed via TMS. A total of 80 relevant studies were identified: 78 EEG studies and only 2 TMS studies. Data extraction and presentation followed PRISMA guidelines.

Of the 78 EEG studies, the authors distinguished between studies in which the subjects' eyes were open and studies in which the subjects' eyes were closed. Of the 33 studies conducted with subjects' eyes open, 22 reported significant alterations in brain oscillations during mobile phone exposure. Of the 48 studies conducted with the subjects' eyes closed, 35 observed significant effects. Depending on the study design, changes in EEG amplitude were heterogeneous, with both increases and decreases reported across all frequency bands. The most common changes were increases in alpha- and beta-band amplitudes. Overall, more increases than decreases were documented. Both TMS studies reported significant modulation of excitability (intracortical facilitation).

This scoping review suggests that mobile phone exposure can modulate neuronal oscillations and cortical excitability. The authors identified major gaps in the evidence base, particularly regarding risk assessments, non-thermal effects, and 5G millimeter wave applications. Hardly any experimental studies exist on these topics. They also highlight limitations, including the small number of TMS studies, which makes the evidence for changes in excitability inconclusive. In addition, the diversity of outcome parameters across EEG studies precluded meta-analysis. Other limitations include imprecise characterization of participants (e.g. age and sex) and the absence of predefined effect sizes and power calculations, which could compromise the interpretability of the results. The authors recommend the following improvements for future work: conducting more 5G studies (especially on millimeter waves), better stratifying subjects by demographic variables, and standardizing experimental parameters, such as field strengths, controls, blinding, crossover design, and technical details of EEG/TMS acquisition.

Editor's note:

The use of PRISMA scoping criteria provides structure and transparency. This review's credibility is bolstered by its systematic categorization (which includes a detailed characterization of radiofrequency fields), its large proportion of double-blind primary studies, and its explicit acknowledgment of methodological limitations. (RH)