Effects of RF‐EMF on the Human Resting‐State EEG—the Inconsistencies in the Consistency. Part 1: Non‐Exposure‐Related Limitations of Comparability Between Studies

The results of studies on possible effects of radiofrequency electromagnetic fields (RF‐EMFs) on human waking electroencephalography (EEG) have been quite heterogeneous. In the majority of studies, changes in the alpha‐frequency range in subjects who were exposed to different signals of mobile phone‐related EMF sources were observed, whereas other studies did not report any effects. In this review, possible reasons for these inconsistencies are presented and recommendations for future waking EEG studies are made. The physiological basis of underlying brain activity, and the technical requirements and framework conditions for conducting and analyzing the human resting‐state EEG are discussed. Peer‐reviewed articles on possible effects of EMF on waking EEG were evaluated with regard to non‐exposure‐related confounding factors. Recommendations derived from international guidelines on the analysis and reporting of findings are proposed to achieve comparability in future studies. In total, 22 peer‐reviewed studies on possible RF‐EMF effects on human resting‐state EEG were analyzed. EEG power in the alpha frequency range was reported to be increased in 10, decreased in four, and not affected in eight studies. All reviewed studies differ in several ways in terms of the methodologies applied, which might contribute to different results and conclusions about the impact of EMF on human resting‐state EEG. A discussion of various study protocols and different outcome parameters prevents a scientifically sound statement on the impact of RF‐EMF on human brain activity in resting‐state EEG. Further studies which apply comparable, standardized study protocols are recommended. Bioelectromagnetics. 2019;40:291–318. © 2019 The Authors. Bioelectromagnetics Published by Wiley Periodicals, Inc.     

Interhemispheric EEG asymmetries during unilateral bright-light exposure and subsequent sleep in humans

We tested whether evening exposure to unilateral photic stimulation has repercussions on interhemispheric EEG asymmetries during wakefulness and later sleep. Because light exerts an alerting response in humans, which correlates with a decrease in waking EEG theta/alpha-activity and a reduction in sleep EEG delta activity, we hypothesized that EEG activity in these frequency bands show interhemispheric asymmetries after unilateral bright light (1,500 lux) exposure. A 2-h hemi-field light exposure acutely suppressed occipital EEG alpha activity in the ipsilateral hemisphere activated by light. Subjects felt more alert during bright light than dim light, an effect that was significantly more pronounced during activation of the right than the left visual cortex. During subsequent sleep, occipital EEG activity in the delta and theta range was significantly reduced after activation of the right visual cortex but not after stimulation of the left visual cortex. Furthermore, hemivisual field light exposure was able to shift the left predominance in occipital spindle EEG activity toward the stimulated hemisphere. Time course analysis revealed that this spindle shift remained significant during the first two sleep cycles. Our results reflect rather a hemispheric asymmetry in the alerting action of light than a use-dependent recovery function of sleep in response to the visual stimulation during prior waking. However, the observed shift in the spindle hemispheric dominance in the occipital cortex may still represent subtle local use-dependent recovery functions during sleep in a frequency range different from the delta range.     

Do people with idiopathic environmental intolerance attributed to electromagnetic fields display physiological effects when exposed to electromagnetic fields? A systematic review of provocation studies

Idiopathic environmental intolerance attributed to electromagnetic fields (IEI‐EMF) is a controversial illness in which people report symptoms that they believe are triggered by exposure to EMF. Double‐blind experiments have found no association between the presence of EMF and self‐reported outcomes in people with IEI‐EMF. No systematic review has assessed whether EMF exposure triggers physiological or cognitive changes in this group. Using a systematic literature search, we identified 29 single or double‐blind experiments in which participants with IEI‐EMF were exposed to different EMF levels and in which objectively measured outcomes were assessed. Five studies identified significant effects of exposure such as reduced heart rate and blood pressure, altered pupillary light reflex, reduced visual attention and perception, improved spatial memory, movement away from an EMF source during sleep and altered EEG during sleep. In most cases, these were isolated results that other studies failed to replicate. For the sleep EEG findings, the results reflected similar changes in the IEI‐EMF participants and a non‐IEI‐EMF control group. At present, there is no reliable evidence to suggest that people with IEI‐EMF experience unusual physiological reactions as a result of exposure to EMF. This supports suggestions that EMF is not the main cause of their ill health. Bioelectromagnetics. Bioelectromagnetics 32:593–609, 2011. © 2011 Wiley Periodicals, Inc.     

Electromagnetic Field Effect or Simply Stress? Effects of UMTS Exposure on Hippocampal Longterm Plasticity in the Context of Procedure Related Hormone Release

Harmful effects of electromagnetic fields (EMF) on cognitive and behavioural features of humans and rodents have been controversially discussed and raised persistent concern about adverse effects of EMF on general brain functions. In the present study we applied radio-frequency (RF) signals of the Universal Mobile Telecommunications System (UMTS) to full brain exposed male Wistar rats in order to elaborate putative influences on stress hormone release (corticosteron; CORT and adrenocorticotropic hormone; ACTH) and on hippocampal derived synaptic long-term plasticity (LTP) and depression (LTD) as electrophysiological hallmarks for memory storage and memory consolidation. Exposure was computer controlled providing blind conditions. Nominal brain-averaged specific absorption rates (SAR) as a measure of applied mass-related dissipated RF power were 0, 2, and 10 W/kg over a period of 120 min. Comparison of cage exposed animals revealed, regardless of EMF exposure, significantly increased CORT and ACTH levels which corresponded with generally decreased field potential slopes and amplitudes in hippocampal LTP and LTD. Animals following SAR exposure of 2 W/kg (averaged over the whole brain of 2.3 g tissue mass) did not differ from the sham-exposed group in LTP and LTD experiments. In contrast, a significant reduction in LTP and LTD was observed at the high power rate of SAR (10 W/kg). The results demonstrate that a rate of 2 W/kg displays no adverse impact on LTP and LTD, while 10 W/kg leads to significant effects on the electrophysiological parameters, which can be clearly distinguished from the stress derived background. Our findings suggest that UMTS exposure with SAR in the range of 2 W/kg is not harmful to critical markers for memory storage and memory consolidation, however, an influence of UMTS at high energy absorption rates (10 W/kg) cannot be excluded.     

Individual differences in the effects of mobile phone exposure on human sleep: rethinking the problem

Mobile phone exposure‐related effects on the human electroencephalogram (EEG) have been shown during both waking and sleep states, albeit with slight differences in the frequency affected. This discrepancy, combined with studies that failed to find effects, has led many to conclude that no consistent effects exist. We hypothesised that these differences might partly be due to individual variability in response, and that mobile phone emissions may in fact have large but differential effects on human brain activity. Twenty volunteers from our previous study underwent an adaptation night followed by two experimental nights in which they were randomly exposed to two conditions (Active and Sham), followed by a full‐night sleep episode. The EEG spectral power was increased in the sleep spindle frequency range in the first 30 min of non‐rapid eye movement (non‐REM) sleep following Active exposure. This increase was more prominent in the participants that showed an increase in the original study. These results confirm previous findings of mobile phone‐like emissions affecting the EEG during non‐REM sleep. Importantly, this low‐level effect was also shown to be sensitive to individual variability. Furthermore, this indicates that previous negative results are not strong evidence for a lack of an effect and, given the far‐reaching implications of mobile phone research, we may need to rethink the interpretation of results and the manner in which research is conducted in this field. Bioelectromagnetics 33:86–93, 2012. © 2011 Wiley Periodicals, Inc.     

Sleep after mobile phone exposure in subjects with mobile phone‐related symptoms

Several studies show increases in activity for certain frequency bands (10–14 Hz) and visually scored parameters during sleep after exposure to radiofrequency electromagnetic fields. A shortened REM latency has also been reported. We investigated the effects of a double‐blind radiofrequency exposure (884 MHz, GSM signaling standard including non‐DTX and DTX mode, time‐averaged 10 g psSAR of 1.4 W/kg) on self‐evaluated sleepiness and objective EEG measures during sleep. Forty‐eight subjects (mean age 28 years) underwent 3 h of controlled exposure (7:30–10:30 PM; active or sham) prior to sleep, followed by a full‐night polysomnographic recording in a sleep laboratory. The results demonstrated that following exposure, time in Stages 3 and 4 sleep (SWS, slow‐wave sleep) decreased by 9.5 min (12%) out of a total of 78.6 min, and time in Stage 2 sleep increased by 8.3 min (4%) out of a total of 196.3 min compared to sham. The latency to Stage 3 sleep was also prolonged by 4.8 min after exposure. Power density analysis indicated an enhanced activation in the frequency ranges 0.5–1.5 and 5.75–10.5 Hz during the first 30 min of Stage 2 sleep, with 7.5–11.75 Hz being elevated within the first hour of Stage 2 sleep, and bands 4.75–8.25 Hz elevated during the second hour of Stage 2 sleep. No pronounced power changes were observed in SWS or for the third hour of scored Stage 2 sleep. No differences were found between controls and subjects with prior complaints of mobile phone‐related symptoms. The results confirm previous findings that RF exposure increased the EEG alpha range in the sleep EEG, and indicated moderate impairment of SWS. Furthermore, reported differences in sensitivity to mobile phone use were not reflected in sleep parameters. Bioelectromagnetics 32:4–14, 2011. © 2010 Wiley‐Liss, Inc.     

Effects of radiation emanating from base transceiver station and mobile phone on sleep,circadian rhythm and cognition in humans – a review

The electromagnetic fields (EMF) are ubiquitous. The base transceiver station (BTS) and mobile phones (MPs) contribute to the generation of EMF around their locations and are regarded as important sources of non-ionizing radiations. The use of mobile phone has increased dramatically in recent years so also the skepticism regarding its effects. In this review, we have made an attempt to scan the key research papers those aimed at elucidating the effects of EMF starting from extreme low frequency (ELF) to radio frequency (RF) through low frequency (LF). We have selected papers that dealt with the effects of radiations emanating from the BTS and MPs on human sleep, circadian rhythm, and cognition. Mostly, we have concentrated on papers published in the last 15 years. We came across conflicting reports. The findings reported in many papers suggest that the exposure to EMF has potentiality to compromise parameters related to sleep quality; in contrast, there are several reports those have given a clean sheet to the EMF exposure. The effects of EMF on circadian rhythms also remain inconclusive. The EMF exposure while did not produce any effect on circadian rhythm of heart rate and blood chemistry, it modulated the rhythms in cortisol and melatonin characterized by a decline in their 24-h circulating levels. The effects of exposure to EMF on cognitive parameters, like performance and memory, are also equivocal. The existing contradictory findings could be attributed to inter-individual variability in tolerance, gender-, and age-dependent differences in response, latitudinal differences in efficacy, variability among employed methodologies and differences in specific absorption rate, frequency of the mobile phone usage, and interaction of EMF with other physiological and environmental factors, among others. The future research should be carried out with added focus on elucidating the modulatory effects of these factors to put an end to the existing controversies on the biological effects of low/RF EMF radiations.     

Dependence of the non-thermal radiofrequency electromagnetic field bioeffects on the typological features of electroencephalogram in humans

In researches with participation of volunteers bioeffects of short-term non-thermal radiofrequency electromagnetic field (RF EMF) exposure were studied. The basic form of brain's reaction was the amplification of energy in a-range in electroencephalogram (EEG) spectra. Dependence of these changes, not only due to the changes of the exposure parameters, but also due to personal EEG typological features was shown. Moderate degree of the alpha frequencies domination in the background promoted development of reaction of a brain to the RF EMF exposure. To a lesser degree it was shown at hyperactivity of this range and, practically, was absent in the conditions of theta- or beta2-range domination in the EEG background with the open and closed eyes. The combination of RF EMF exposure and monotonous activity has authentically strengthened result, keeping the basic form of reaction (energy amplification in the alpha range of EEG spectrum) and dependence on EEG typological features.     

Human sleep under the influence of pulsed radiofrequency electromagnetic fields: A polysomnographic study using standardized conditions

To investigate the influence of radiofrequency electromagnetic fields (EMFs) of cellular phone GSM signals on human sleep electroencephalographic (EEG) pattern, all-night polysomnographies of 24 healthy male subjects were recorded, both with and without exposure to a circular polarized EMF (900 MHz, pulsed with a frequency of 217 Hz, pulse width 577 μs, power flux density 0.2 W/m². Suppression of rapid eye movement (REM) sleep as well as a sleep-inducing effect under field exposure did not reach statistical significance, so that previous results indicating alterations of these sleep parameters could not be replicated. Spectral power analysis also did not reveal any alterations of the EEG rhythms during EMF exposure. The failure to confirm our previous results might be due to dose-dependent effects of the EMF on the human sleep profile. Bioelectromagnetics 19:199–202, 1998. © 1998 Wiley-Liss, Inc.     

1950 MHz radiofrequency electromagnetic fields do not aggravate memory deficits in 5xFAD mice

The increased use of mobile phones has generated public concern about the impact of radiofrequency electromagnetic fields (RF‐EMF) on health. In the present study, we investigated whether RF‐EMFs induce molecular changes in amyloid precursor protein (APP) processing and amyloid beta (Aβ)‐related memory impairment in the 5xFAD mouse, which is a widely used amyloid animal model. The 5xFAD mice at the age of 1.5 months were assigned to two groups (RF‐EMF‐ and sham‐exposed groups, eight mice per group). The RF‐EMF group was placed in a reverberation chamber and exposed to 1950 MHz electromagnetic fields for 3 months (SAR 5 W/kg, 2 h/day, 5 days/week). The Y‐maze, Morris water maze, and novel object recognition memory test were used to evaluate spatial and non‐spatial memory following 3‐month RF‐EMF exposure. Furthermore, Aβ deposition and APP and carboxyl‐terminal fragment β (CTFβ) levels were evaluated in the hippocampus and cortex of 5xFAD mice, and plasma levels of Aβ peptides were also investigated. In behavioral tests, mice that were exposed to RF‐EMF for 3 months did not exhibit differences in spatial and non‐spatial memory compared to the sham‐exposed group, and no apparent change was evident in locomotor activity. Consistent with behavioral data, RF‐EMF did not alter APP and CTFβ levels or Aβ deposition in the brains of the 5xFAD mice. These findings indicate that 3‐month RF‐EMF exposure did not affect Aβ‐related memory impairment or Aβ accumulation in the 5xFAD Alzheimer's disease model. Bioelectromagnetics. 37:391–399, 2016. © 2016 The Authors Bioelectromagnetics published by Wiley Periodicals, Inc. on behalf of Bioelectromagnetics Society.     

Autoimmune process after long-term low-level exposure to electromagnetic field (experimental results). Part I. Mobile communications and changes in electromagnetic conditions for the population. Need for additional substantiation of existing hygienic standards

Mobile communications provides a new source of electromagnetic exposure for almost the whole population of Russia. For the first time in the history of civilization, the brain of mobile phone users is exposed to localized radiofrequency (RF) electromagnetic fields (EMF). Base stations are a factor in the exposure of the population. Existing standards for limiting exposure do not account for the role of base stations as a source of EMF and cannot guarantee the absence of adverse health effects. It has become necessary to obtain reliable information to expand databases for the development of new standards. As recommended by the World Health Organization, an additional experiment is performed under the supervision of foreign experts, which shows changes in autoimmune status in rats after long-term low-level RF EMF exposure with an incident power of 500 μW/cm².     

Design and dosimetric analysis of a 385 MHz TETRA head exposure system for use in human provocation studies

A new head exposure system for double‐blind provocation studies investigating possible effects of terrestrial trunked radio (TETRA)‐like exposure (385 MHz) on central nervous processes was developed and dosimetrically analyzed. The exposure system allows localized exposure in the temporal brain, similar to the case of operating a TETRA handset at the ear. The system and antenna concept enables exposure during wake and sleep states while an electroencephalogram (EEG) is recorded. The dosimetric assessment and uncertainty analysis yield high efficiency of 14 W/kg per Watt of accepted antenna input power due to an optimized antenna directly worn on the subject's head. Beside sham exposure, high and low exposure at 6 and 1.5 W/kg (in terms of maxSAR10g in the head) were implemented. Double‐blind control and monitoring of exposure is enabled by easy‐to‐use control software. Exposure uncertainty was rigorously evaluated using finite‐difference time‐domain (FDTD)‐based computations, taking into account anatomical differences of the head, the physiological range of the dielectric tissue properties including effects of sweating on the antenna, possible influences of the EEG electrodes and cables, variations in antenna input reflection coefficients, and effects on the specific absorption rate (SAR) distribution due to unavoidable small variations in the antenna position. This analysis yielded a reasonable uncertainty of <±45% (max to min ratio of 4.2 dB) in terms of maxSAR10g in the head and a variability of <±60% (max to min ratio of 6 dB) in terms of mass‐averaged SAR in different brain regions, as demonstrated by a brain region‐specific absorption analysis. Bioelectromagnetics 33:594–603, 2012. © 2012 Wiley Periodicals, Inc.     

Electromagnetic fields (GSM 1800) do not alter blood-brain barrier permeability to sucrose in models in vitro with high barrier tightness

We previously reported that electromagnetic fields (EMFs) [GSM 1800 standard (Global System for Mobile Communications, 1800 MHz)] increased sucrose permeation across the blood-brain barrier (BBB) in vitro. The cell culture model used in our previous study was comprised of rat astrocytes in coculture with porcine brain microvascular endothelial cells (PBECs). In this study, after optimization of cell culture conditions, distinctly improved barrier tightness was observed, accompanied by a loss of susceptibility to EMF-related effects on BBB permeability. Cell cultures were exposed for 1-5 days at an average specific absorption rate (SAR) of 0.3 W/kg in the identical exposure system as described before. To quantify barrier tightness, sucrose permeation across exposed PBEC was measured and compared to values of sham exposed cells and to a control group. Additionally, observations in the BBB coculture system were complemented by similar experiments using two other in vitro models, composed of PBEC monocultures with or without serum. These three models display distinctly higher barrier tightness than the previously used system. In all three BBB models, sucrose permeation across the cell layers remained unaffected by exposure to a GSM 1800 field for up to 5 days. We thus could not confirm enhanced permeability of the BBB in vitro after EMF exposure as reported before since the in vitro barrier tightness in these experiments is now more like that of the in vivo situation.     

Early and Later Life Stress Alter Brain Activity and Sleep in Rats

Exposure to early life stress may profoundly influence the developing brain in lasting ways. Neuropsychiatric disorders associated with early life adversity may involve neural changes reflected in EEG power as a measure of brain activity and disturbed sleep. The main aim of the present study was for the first time to characterize possible changes in adult EEG power after postnatal maternal separation in rats. Furthermore, in the same animals, we investigated how EEG power and sleep architecture were affected after exposure to a chronic mild stress protocol. During postnatal day 2–14 male rats were exposed to either long maternal separation (180 min) or brief maternal separation (10 min). Long maternally separated offspring showed a sleep-wake nonspecific reduction in adult EEG power at the frontal EEG derivation compared to the brief maternally separated group. The quality of slow wave sleep differed as the long maternally separated group showed lower delta power in the frontal-frontal EEG and a slower reduction of the sleep pressure. Exposure to chronic mild stress led to a lower EEG power in both groups. Chronic exposure to mild stressors affected sleep differently in the two groups of maternal separation. Long maternally separated offspring showed more total sleep time, more episodes of rapid eye movement sleep and higher percentage of non-rapid eye movement episodes ending in rapid eye movement sleep compared to brief maternal separation. Chronic stress affected similarly other sleep parameters and flattened the sleep homeostasis curves in all offspring. The results confirm that early environmental conditions modulate the brain functioning in a long-lasting way.     

Effects of exposure to low level radiofrequency fields on acetylcholine release in hippocampus of freely moving rats

Some central cholinergic effects have been reported in animals after acute exposure to radiofrequency electromagnetic field at low intensity. We studied acetylcholine (ACh) release in the brain of freely moving rats exposed for 1 h during the day to a 2.45 GHz continuous wave radiofrequency field (RF) (2 or 4 mW/cm(2)) or exposed for 1 or 14 h during the night to a 800 MHz field modulated at 32 Hz (AM 200 mW/cm(2)). Measurements were performed by microdialysis using a membrane implanted through the upper CA1 region of the hippocampus. After irradiation with the 2.45 GHz RF, rats exposed at 2 mW/cm(2) did not show a significant modification of Ach release, whereas those exposed at 4 mW/cm(2) showed a significant 40% decrease in mean ACh release from hippocampus. This decrease was maximal at 5 h post exposure. Exposure to the 800 MHz RF for 1 h did not cause any significant effect, but exposure for 14 hrs induced a significant 43% decrease in ACh release during the period 11 p.m.-4 a.m. compared to control rats. In the control group we observed an increase of ACh release at the beginning of the night, which was linked to the waking period of rats. This normal increase was disturbed in rats exposed overnight to the 800 MHz RF. This work indicates that neurochemical modification of the hippocampal cholinergic system can be observed during and after an exposure to low intensity RF.     

Electroencephalogram bands modulated by vigilance states in an anuran species: a factor analytic approach

Dramatic changes in neocortical electroencephalogram (EEG) rhythms are associated with the sleep–waking cycle in mammals. Although amphibians are thought to lack a neocortical homologue, changes in rest–activity states occur in these species. In the present study, EEG signals were recorded from the surface of the cerebral hemispheres and midbrain on both sides of the brain in an anuran species, Babina daunchina, using electrodes contacting the meninges in order to measure changes in mean EEG power across behavioral states. Functionally relevant frequency bands were identified using factor analysis. The results indicate that: (1) EEG power was concentrated in four frequency bands during the awake or active state and in three frequency bands during rest; (2) EEG bands in frogs differed substantially from humans, especially in the fast frequency band; (3) bursts similar to mammalian sleep spindles, which occur in non-rapid eye movement mammalian sleep, were observed when frogs were at rest suggesting sleep spindle-like EEG activity appeared prior to the evolution of mammals.     

Local exposure of the rat cortex to radiofrequency electromagnetic fields increases local cerebral blood flow along with temperature

Few studies have shown that local exposure to radiofrequency electromagnetic fields (RF) induces intensity-dependent physiological changes, especially in the brain. The aim of the present study was to detect reproducible responses to local RF exposure in the parietal cortex of anesthetized rats and to determine their dependence on RF intensity. The target cortex tissue was locally exposed to 2-GHz RF using a figure-eight loop antenna within a range of averaged specific absorption rates (10.5, 40.3, 130, and 263 W/kg averaged over 4.04 mg) in the target area. Local cerebral blood flow (CBF) and temperatures in three regions (target area, rectum, and calf hypodermis) were measured using optical fiber blood flow meters and thermometers during RF exposure. All parameters except for the calf hypodermis temperature increased significantly in exposed animals compared with sham-exposed ones during 18-min exposures. Dependence of parameter values on exposure intensity was analyzed using linear regression models. The elevation of local CBF was correlated with temperature rise in both target and rectum at the end of RF exposure. However, the local CBF elevation seemed to be elevated by the rise in target temperature, but not by that of the rectal temperature, in the early part of RF exposure or at low-intensity RF exposure. These findings suggest that local RF exposure of the rat cortex drives a regulation of CBF accompanied by a local temperature rise, and our findings may be helpful for discussing physiological changes in the local cortex region, which is locally exposed to RF.     

Influence of a 902.4 MHz GSM signal on the human visual system: investigation of the discrimination threshold

The proximity of a mobile phone to the human eye raises the question as to whether radiofrequency (RF) electromagnetic fields (EMF) affect the visual system. A basic characteristic of the human eye is its light sensitivity, making the visual discrimination threshold (VDThr) a suitable parameter for the investigation of potential effects of RF exposure on the eye. The VDThr was measured for 33 subjects under standardized conditions. Each subject took part in two experiments (RF-exposure and sham-exposure experiment) on different days. In each experiment, the VDThr was measured continuously in time intervals of about 10 s for two periods of 30 min, having a break of 5 min in between. The sequence of the two experiments was randomized, and the study was single blinded. During the RF exposure, a GSM signal of 902.4 MHz (pulsed with 217 Hz) was applied to the subjects. The power flux density of the electromagnetic field at the subject location (in the absence of the subject) was 1 W/m(2), and numerical dosimetry calculations determined corresponding maximum local averaged specific absorption rate (SAR) values in the retina of SAR(1 g) = 0.007 W/kg and SAR(10 g) = 0.003 W/kg. No statistically significant differences in the VDThr were found in comparing the data obtained for RF exposure with those for sham exposure.     

1950 MHz IMT‐2000 field does not activate microglial cells in vitro

Given the widespread use of the cellular phone today, investigation of potential biological effects of radiofrequency (RF) fields has become increasingly important. In particular, much research has been conducted on RF effects on brain function. To examine any biological effects on the central nervous system (CNS) induced by 1950 MHz modulation signals, which are controlled by the International Mobile Telecommunication‐2000 (IMT‐2000) cellular system, we investigated the effect of RF fields on microglial cells in the brain. We assessed functional changes in microglial cells by examining changes in immune reaction‐related molecule expression and cytokine production after exposure to a 1950 MHz Wideband Code Division Multiple Access (W‐CDMA) RF field, at specific absorption rates (SARs) of 0.2, 0.8, and 2.0 W/kg. Primary microglial cell cultures prepared from neonatal rats were subjected to an RF or sham field for 2 h. Assay samples obtained 24 and 72 h after exposure were processed in a blind manner. Results showed that the percentage of cells positive for major histocompatibility complex (MHC) class II, which is the most common marker for activated microglial cells, was similar between cells exposed to W‐CDMA radiation and sham‐exposed controls. No statistically significant differences were observed between any of the RF field exposure groups and the sham‐exposed controls in percentage of MHC class II positive cells. Further, no remarkable differences in the production of tumor necrosis factor‐α (TNF‐α), interleukin‐1β (IL‐1β), and interleukin‐6 (IL‐6) were observed between the test groups exposed to W‐CDMA signal and the sham‐exposed negative controls. These findings suggest that exposure to RF fields up to 2 W/kg does not activate microglial cells in vitro. Bioelectromagnetics 31:104–112, 2010. © 2009 Wiley‐Liss, Inc.