The human brain consists of neuronal networks which can be in different states of activation. Brain activity can be measured by e.g. changes in electric voltage via EEG (electroencephalography). This can be done during a relative resting state of the brain (resting EEG), during sleep (sleep EEG) and during cognitive tasks. In the latter case so called event-related potentials are recorded.
The brain is exposed to relatively high specific absorption rates (SARs) during a mobile phone call, compared to the rest of the body (Hossmann et al. 2003, p.49), because of the close proximity of the mobile phone to the head. Some authors advance the hypothesis that a certain amount of radiofrequency fields emitted by mobile phones is absorbed through the skull and reaches the brain. This might lead to a physiological interaction between these radiofrequency electromagnetic fields and human cerebral activity (Valentini et al. 2007, p.1).
The effects of mobile communication related radiofrequency electromagnetic fields on the brain activity have been investigated in a multitude of studies. An overview of all experimental mobile phone-related studies on brain activity can be found in the study overview on mobile phones in the EMF-Portal. In addition, the effects of mobile phone exposure on sleep EEG are also presented in the chapter "sleep". Different international and national committees have evaluated the existing data and are not consistent regarding the evidence of an effect on brain activity. However, they did agree in terms of possible consequences for human health.
At international level, the World Health Organization (WHO), in its last short statement (Fact sheet № 193, 2014), saw no consistent evidence of adverse health effects from radiofrequency electromagnetic fields. This assessment of the WHO is shared by all in the following committees.
At European level, the Scientific Committee on Emerging and Newly Identified Health Risks of the EU (SCENIHR, 2015, p.126 f) sees some evidence of small effects on brain activity in a synopsis of all studies. In the resting EEG, there is mainly an increase in the alpha wave band activity described although SCENIHR criticizes the quality of some older studies (e.g. due to a missing double-blind study design). It deems the results of recent studies as partly contradictory and inconsistent. In sleep EEG, SCENIHR sees changes in several EEG bands und sleep stages and disagrees with other experts (e.g. the Swedish Radiation Safety Authority (SSM), 2013, p.9), who claim that effects on sleep EEG are consistent. SCENIHR sees no consistent effects regarding event-related potentials, either. The committee indicates that the results of some studies (e.g. Croft et al. 2010 and Vecchio et al. 2010) suggest age-related effects, which have not yet been sufficiently investigated.
The German Commission on Radiological Protection (SSK, 2011, p.24 f) judges similarly to SCENIHR regarding effects on the brain activity and demands that further research should be done with stringent experimental protocols and the investigation of possible age-related effects. On the contrary, the Federal Office for the Environment (FOEN, 2014, p.22 f (in German)) in Switzerland, sees sufficient evidence for changes to the EEG activity through mobile communication exposure. Concretely, the FOEN sees evidence for an increased activity in the alpha wave band when awake and an increased activity in the frequency band from 12-15 Hz during sleep.
To summarize, it can be concluded, that international and national expert committees consider that small effects from mobile communication related radiofrequency electromagnetic fields on the brain activity are possible but there is not sufficient evidence for relevant health effects. A new and detailed opinion from the WHO regarding the effects of radiofrequency electromagnetic fields is expected in 2016 (Fact sheet № 193, 2014).