16/02/2014
Modeling of EEG Electrode Artifacts and Thermal Ripples in Human Radiofrequency Exposure Studies
Manuel Murbach, Esra Neufeld, Maria Christopoulou, Peter Achermann, and Niels Kuster, Bioelectromagnetics, Volume 35, Issue 4, pp. 273-283, online February 13, 2014.
We investigated the effects of metallic electroencephalography (EEG) electrodes and leads on radiofrequency (RF) exposure of the human head. It has been hypothesized that observed RF effects on the brain may be explained by (1) enhanced induced fields around the electrodes, (2) the subsequent temperature increase around the electrodes, or (3) RF-induced thermal pulsing caused by localized exposure in the head. We evaluated these three hypotheses by means of both numerical and experimental assessments made with appropriate phantoms and anatomical human models. Typical and worst-case electrode placements were examined at 900 and 2140 MHz. The results demonstrate that the induced field, temperature, and thermal ripple enhancements assessed are too small to account for the observed RF effects. Thus, the mechansism of RF–induced changes in the EEG power spectrum remains unknown. Other potential hypotheses to explain the effects include oscillatory brain activity caused by sensory perception of RF and non-synaptic or ephaptic coupling of cortical neurons.
The scientific and technical impact of this study can be summarized as:
- The maximum enhancements of the induced fields due to the presence of the EEG electrodes are small, <20% for psSAR10g.
- The temperature increase near the electrode is small, <0.1°C.
- The thermal ripple caused by GSM modulation is very small, <0.001°C.
- The presence of the EEG assemblies is very unlikely to cause the reported changes in the EEG power spectrum.