Study overviews

Cognition includes all mechanisms of information processing in the brain that are related to perception and recognition. Cognitive skills include for example attention, discrimination, learning ability, ability to abstract, creativity, planning, orientation and executive control.

Psychomotor functions are psychological processes (e.g. emotion, concentration, individual personality characteristics) that have an impact on motor functions and kinesic behaviour.

Memory functions describe the ability of the nervous system to store, organize and retrieve incoming information. The ability to build up memory is an indicator for neuronal plasticity and the basis for learning processes.

Many studies investigate the effects of acute mobile phone exposure to the head and associated brain regions. The aim of these studies is to clarify whether radiofrequency electromagnetic fields emitted by mobile phones have an impact on neuronal activity in the brain and its associated functions. Possible effects could evolve from heating (thermal effect) and resulting vasodilation. The rate at which energy is absorbed (specific absorption rate SAR) in body tissues per time unit is a basic parameter for the evaluation of the thermal effect of radiofrequency. Some authors support the hypothesis that electromagnetic fields change the electrical potentials in cells and consequently influence neurons with highly excitable, polarized membranes (athermal effect). Later, these thermal and athermal effects can lead to indirect effects of mobile phones, e.g. changes in memory functions, learning ability or attention. These effects can be beneficial for performance (e.g. faster information processing speed, improved attention and memory), but also detrimental (e.g. limited selective attention, memory impairments, increased accident rate due to simultaneous use of mobile phones). Another hypothesis concerns the proximity of the mobile phone to the parietal lobe of the brain that can have effects on spatial information processing and in turn influence psychomotor functions.

To assess the effects of electromagnetic fields on memory, cognitive and psychomotor functions, studies are performed with humans and animals (mainly rats and mice). The following test procedures (computerized tests and/or paper- and pencil tests) are frequently used:

• attention and concentration tests (e.g. reaction time tests, digit spans, cancellation tests, sorting tasks)
• tests on cognitive information processing speed (e.g. arithmetic problems, verbal fluency tests)
• learning and memory tests (e.g. lists of paired words, drawing tests, real or virtual maze tests)
• self-reported questionnaires (e.g. subjective symptoms, mood)
• physiological data: EEG, ECG, skin resistance

In experimental animal studies, primarily learning ability and memory functions are studied by means of labyrinth tests.

Measuring the effects of electromagnetic fields on cognitive, psychomotor and memory functions beyond a standardized test environment is difficult. Frequently, blind studies or double-blind studies are conducted to prevent demand effects due to expectations or behaviours of the participants or the experimenters. However, as most studies are conducted under controlled conditions on selective samples, the results are of limited ecological validity. Studies on the effects of mobile phones on cognitive, psychomotor and memory functions vary largely in the used exposure parameters and the applied tests. It is thus problematic to compare and evaluate the partly contradicting findings.

In total, there are currently 45 studies (date: March 2009) on the effects of electromagnetic fields in the mobile phone frequency range on cognitive, psychomotor and memory functions. From these, 20 studies investigated the possible effects of mobile phones on measures of cognitive performance, 11 studies investigated effects on memory functions, 5 studies examined psychomotoric parameters, 4 studies assessed effects on attention, 4 studies examined effects on EEG during a cognitive task or physiological parameters and 3 studies examined effects on neural activity and brain development. Altogether, 38 studies were conducted in samples with humans and 7 studies were performed in rats or mice. Some studies indicate that short-term exposure with mobile phones can improve attentional processes (e.g. articles 8723, 10074) and memory functions (e.g. article 10014). Other studies demonstrate that long-term exposure with mobile phones can be accompanied by impairments of basic cognitive processes (e.g. article 10779). Long-term studies are not yet available.

Generally, the evaluation of possible effects of electromagnetic fields on cognitive, psychomotor and memory functions is a complex and time-consuming process that has to be enforced by an expert body due to the aformentioned limitations (e.g. different study designs, tests). In the course of such an evaluation, all publications from different study types (animal studies, experimental studies with volunteers, public surveys) with similar exposure parameters and endpoints have to be collected and evaluated regarding their quality (e.g. dosimetry, study design, sample size, statistics). The results have to reproducible and should be evaluated with regard to comparable research studies.

At the international level, the WHO is particularly responsible for statements on the effects of electromagnetic fields. For public health related issues, specific recommendations are made available (WHO 2000).

At the national German level, the federal office for radiation protection (Bundesamt für Strahlenschutz, BfS) is the responsible authority. They also provide statements on the effects of electromagnetic fields. In 2009, the federal office for radiation protection (Bundesamt für Strahlenschutz, BfS) has published a review on the literature concerning "Brain, cognition and sleep" (BfS 2009). In Germany, the Strahlenschutzkomission (comittee for radiation protection) at the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit) also provides statements on the effects of electromagnetic fields. In a statement from 2001 on limit values and provisions to protect the public from electromagnetic fields (article 10532), all scientific studies on radiofrequency electromagnetic fields that were published since 1998 were evaluated. One subtopic of the evaluation referred to effects on cognitive functions in humans, with the following conclusion: "Due to the multiplicity of investigated different reaction time paradigms, that show partly speeding effects under exposure, as well as slower reaction times under exposure, a clear evaluation is not possible. However, there are some indications for a potential influence of exposure on physiological processes. Further research is needed to clarify whether the use of mobile phones influences the performance capacity of the brain."

An evaluation of 150 scientific studies on radiofrequency exposure of the Swiss Federal Office of the Environment (FOEN) from 2007 summarized the health effects of radio frequency exposure on several endpoints (article 15806). For the subtopic "cognitive functions" the following conclusions were drawn: "In some studies longer reaction times were observed under exposure, several other studies did not reveal statistically significant differences between exposure and sham exposure. [...] Regarding the error rates, older literature as well as more recent studies mostly did not show any effects of exposure. In single studies, the number of correct responses was increased or decreased. [...] The methodological quality of the latest studies has improved markedly compared to former studies. Limitations are still present regarding the detailed description of the exposure. The comparability of studies is limited due to variations in intensity and duration of exposure and different testing times. In most studies, the neuropsychological tests were performed during the exposure while some studies performed the tests after the exposure. Moreover, most studies have small sample sizes and limitations of the statistical power are rarely discussed. Also, studies with larger samples did not reveal significant effects of exposure. Positive results could be simply coincidental. [...] In sum, the evidence for short term effects of mobile phone exposure on cognitive functions has changed due to inconsistent results from the latest experimental studies. In contrast to former categorizations of the effects as 'likely', effects are now downgraded to 'possible'. Effects of longterm exposure to mobile phone antennas cannot be evaluated yet. Here, estimations can only be done based on future population-based studies with suitable measurements of exposure conditions."

The following authors and expert bodies provided reviews and comments on the effects of electromagnetic fields in the frequency band of mobile phones, especially with regard to influences on cognitive, psychomotor and memory functions:

• Barth et al. 2012
• Regel et al. 2011
• Valentini et al. 2010
• Barth et al. 2008
• Sienkiewicz et al. 2005
• Hamblin et al. 2002

This text has been edited with the valuable assistance of Mrs. Dr. Cornelia Sauter (clinical psychologist and health psychologist, Charité Berlin, Germany).