Bioelectromagnetics 31:380^390 (2010)

No Effect of TETRAHand PortableTransmission Signals on Human Cognitive

Function and Symptoms

Ingunn S. Riddervold,1 S,ren K. Kj/rgaard,1* Gert F. Pedersen,2 NielsT. Andersen,3

Ondrej Franek,2 Anders D. Pedersen,4 Torben Sigsgaard,1 Robert Zachariae,5

Lars M,lhave,1 and J,rgen B. Andersen2

1Department of Environmental and OccupationalMedicine, School of Public Health,University ofAarhus, Aarhus, Denmark

2Department of Electronic Systems, University ofAalborg, Aalborg, Denmark3Department of Biostatistics, School of Public Health, University ofAarhus,

Aarhus, Denmark4HammelNeurorehabilitation andResearch Center, Hammel, Denmark

5PsychooncologyResearchUnit, AarhusUniversity Hospital, Aarhus, Denmark

Current radio frequency radiation exposure guidelines rest on well-established thermal effects.However, recent research into analogue and digital transmission fields at levels covered by theexposure guidelines has indicated possible detrimental effects on human cognitive performance. Toinvestigate this, we conducted a controlled climate chamber study of possible changes in cognitiveperformance in healthy volunteers exposed to transmission signals from TETRA hand portables(TETRA handsets). The trial deployed a balanced, randomized, double-blinded cross-over design.Performance on different paper-and-pencil, auditory and computer-based cognitive tasks wasmonitored in 53 male volunteers (mean age 36.41 years, SD 8.35) during 45-min exposure to a TETRAhandset and sham control signals remotely controlled from a laboratory more than 100 km away. Themain cognitive outcome was the Trail Making B (TMB) test. In addition, the participants completed acomputer-based questionnaire measuring self-reported psychological and physical symptoms. Nostatistically significant differences (P< 0.05) between the TETRA and sham conditions were foundfor either TMB (estimated difference 3.8%, confidence interval (CI) �1.6% to 9.2%) or any of theremaining cognitive tasks or symptoms. In conclusion, we found no evidence that brief exposure tohand-held TETRA transmitters’ affects human cognitive function or subjective symptoms.Bioelectromagnetics 31:380–390, 2010. � 2010 Wiley-Liss, Inc.

Key words: TETRA; exposure study; humans; cognitive function; symptoms

INTRODUCTION

Terrestrial Trunked Radio (TETRA) is a Europeanopen standard digital mobile radio communicationsystem agreed upon in the early 1990s and administeredby the European Telecommunications Standards Insti-tute [ETSI, 2009]. TETRA has primarily been devel-oped to enable the deployment of secure, digitalProfessional Mobile Radio (PMR) services requiredby the public safety and emergency services (police, firebrigade, and ambulance services). TETRA technologyhas already been adopted by emergency services incountries around the world. The TETRA system isspecified to work within the VHF and UHF bands (150–900 MHz), and most often operates at frequencies around400 MHz. The lower frequency means that TETRA isless vulnerable to interference, which is a vital aspect ofcommunications for the emergency services.

Current radiofrequency radiation exposure guide-lines are based upon well-established thermal effectsdetermined by the International Commission onNon-Ionizing Radiation Protection [ICNIRP, 1998].However, one of the TETRA features is that the signal is

=2010Wiley-Liss, Inc.

——————Grant sponsor: Danish Strategic Research Council ‘‘ProgrammeCommission on Non-ionizing Radiation’’ (2103-05-008).

*Correspondence to: Søren K. Kjærgaard, School of PublicHealth, University of Aarhus, Bartholins Alle 2, Building 1260,DK-8000 Aarhus C, Denmark. E-mail: skk@mil.au.dk

Received for review 13 March 2009; Accepted 19 December 2009

DOI 10.1002/bem.20571Published online 8 March 2010 in Wiley InterScience(www.interscience.wiley.com).

transmitted in bursts that repeat. The result is a powermodulation of some of the radio frequency (RF) signalsat a frequency of 17.6 Hz (times per second) [NRPB,2001]. This pulsing has led to concerns about its effecton health. As this pulsing only occurs for transmissionfrom the different portable TETRA transmitters andnot from the base stations, most concerns are related tothe effects on the users of these transmitting devices.Currently, only little is known about the potentialeffects of exposure to signals in the TETRA frequencybands.

The effects of electromagnetic fields (EMF) on thecirculatory and nervous systems have been the subjectof great interest for several years, because electricimpulses generated in these systems by outer electricand magnetic fields, in theory, may disturb theirfunction. Among the possible effects are changesin neuronal electrical activity, energy metabolism,genomic responses, neurotransmitter balance, blood-barrier permeability, cognitive function and sleep,and various forms of brain damage [Hossmann andHermann, 2003]. Recently published reviews havefocused on interaction between RF fields and biologicaltissues [Challis, 2005], and neurophysiologic andbehavioral effects [Cook et al., 2002, 2006; Sienkiewiczet al., 2005; Valentini et al., 2007].

Assessing the effects of EMF on perception,cognition and behavior is typically measured by meansof standardized performance tasks [Cook et al., 2006],and exposure to RF has been associated with effects ondifferent cognitive functions (e.g., psychomotor speed,attention and working memory). Previous research withmobile phones has identified non-thermal effects ofRF on cognitive performance at levels within theguidelines. These effects include a decrease in responselatency (participants responded more quickly) onsimple reaction time, choice reaction time, vigilance,subtraction and working memory tasks [Preece et al.,1999; Koivisto et al., 2000a,b; Edelstyn and Oldershaw,2002; Smythe and Costall, 2003]. Effects on responseaccuracy, including a decrease in accuracy on a choicereaction time task and an increase in accuracy onvigilance and spatial memory tasks, have also beenreported [Preece et al., 1999; Koivisto et al., 2000b;Smythe and Costall, 2003].

Conflicting findings question whether RF expo-sure may produce effects of sufficient magnitudeto influence cognitive behavior. Critical review andcomparison of previous studies reveals several meth-odological inconsistencies, including the use ofnon-standardized exposure systems and insufficientstatistical analyses that may have resulted in type-1errors and failure to replicate previous significantresults when using improved methodology and are

some of the possible explanations for the inconsistentfindings. Recently two reviews have assessed theproblem [ETSI, 2009; SCENIHR, 2009], and SCE-NIHR concluded that there is some evidence that RFfields can influence EEG patterns and sleep in humans.However, the health relevance is uncertain and mech-anistic explanation is lacking. Further investigation ofthese effects is needed. Other studies on functions/aspects of the nervous system, such as cognitivefunctions, sensory functions, structural stability andcellular responses show no or no consistent effects.’

The objectives of the present study were toemploy a standard exposure system to emulate theTETRA RF fields in a controlled environment, andto identify whether brief TETRA RF exposure iscapable of producing acute effects on specific aspectsof cognitive performance. Our main hypothesis wasthat exposure to a TETRA handset signal will causea reduction in processing speed and executivefunctions of the brain, measured by means of the TrailMaking B (TMB) test. In our secondary and moreexplorative hypothesis, we expected that TETRA-related EMF would cause a reduction in generalcognitive performance as measured by various cogni-tive tests. We also expected an increase in self-reportedsymptoms.

MATERIALS AND METHODS

Design

The study was carried out with a randomized,double-blind, cross-over design using the two differentLatin squares to ensure that both exposure orders wererepresented equally. The participants were allocated tothe two possible exposure orders at random; random-ization was carried out by a statistician. During thesessions, neither the participants nor the investigatorswere aware of the exposures. The investigator monitor-ing the exposure controlled the sessions entirely overthe Internet and had no contact with the participantsor research staff during the experiment. In praxis, thiswas carried out by a remotely placed engineer who setthe equipment according to the randomization, andwho could inspect the intended exposure as well asthe background exposure. The intended exposure wasdirectly measured or sensed in the chamber when theswitch was in the bottom position, and the backgroundexposure was sensed when the switch was in the otherposition using the exposure antenna (see Fig. 2 for thesetup).

All participants attended exposure sessions, shamand TETRA, with a minimum of 24 h between eachsession. The two exposure sessions were conducted on

TETRAPortables and Cognitive Performance 381

Bioelectromagnetics

separate days at about the same time each day. Eachsession included completion of a computer-basedquestionnaire at baseline, followed by a 45-minexposure. During exposure, participants completed anumber of paper-and-pencil, auditory and computer-based tests, and then completed the questionnairea second time at the end of exposure.

Participants

As the TETRA handset is not intended for use bythe general public, the predominant exposure fromthese devices will arise in the course of work for serviceemployees [NRPB, 2001]. A total of 53 male volunteerscomposed of employees from the emergency services(police, fire and paramedics) in Aarhus, Denmarkcompleted the study. Ages ranged from 25 to 49 years(mean 36.41 years), weight from 63 to 101 kg(mean 84.33 kg), and height from 171 to 194 cm (mean182.78 cm). All participants were right-handed. Parti-cipants were enrolled on a ‘first-come-first-served’basis. Prior to the study, all volunteers underwent astandard medical assessment consisting of history andclinical examination. Exclusion criteria were a medicalhistory of head injuries and/or neurological/psychiatricdiseases. Further exclusion criteria were based on theresults of two tasks performed after the medicalexamination: the Danish Adult Reading Test (DART)and TMB. The exclusion criteria were test resultsoutside the range of the normative mean� 2 SD [Gadeand Mortensen, 1984; Warrington, 1984]. Informedwritten consent was required from all participants.The study was approved by The Aarhus CountyHuman Study Review Board in accordance with theregulations for the protection of the participants(Ref. no. 20050032).

Exposure Facilities and Exposure Generation

The study was conducted at the Department ofEnvironmental and Occupational Medicine, Universityof Aarhus. Sessions took place under controlledconditions in a 33.4 m3 climate chamber made ofaluminum to improve shielding in the chamber fromEMF outside the chamber. Inside the chamber, thewalls, floor and ceiling were partly covered with RFabsorbers to prevent reflections (see Fig. 1). All non-coaxial cables to and from the chamber were filtered atthe entrance, and ferrite beads were mounted on thecables to suppress all common mode signals. Further-more, there was no main power (230 V 50 Hz) in thechamber and all lights were fiber optic or 12 V DCpowered. Except for cables to the press pad and the PCscreen, which was DC powered, there were no othernon-intended electromagnetic radiators in the chamber.

During exposure, participants sat at a desk insidethe chamber (see Fig. 1). Throughout each session, theparticipant was asked to maintain a sitting posture in achair next to the table. Environmental conditions weremonitored and kept constant throughout the experimentby an air-conditioning system controlling airflow andtemperature.

To generate the TETRA exposure signal, astandard TETRA handset was used (MotorolaMTH800, Chicago, IL) in direct mode operation(DMO). The RF output from the TETRA handset wasconnected via a coaxial cable from the external antennaoutput to a controllable attenuator, an amplifier, acoupler for monitoring the exposure, and finally to theexposure antenna in the chamber (see Fig. 2). TheTETRA generating handset was running in a 1 minsequence with the TETRA transmitter (talk button) onfor 54 s and off for 6 s to emulate a high exposurescenario without excluding the special end-of-talkexposure which takes 5.1 s after releasing the talkbutton.

Studies of the radiation characteristics of ahandset held next to head by the hand have shown thatthe hand causes a large variation in the head exposure[Pedersen et al., 2000; Pelosi et al., 2009]. Therefore, itwas decided to introduce an exposure setup where thetest person did not hold the handset, but instead a specialplastic helmet was used to hold the radiating handset(see Fig. 3). Actually, a meander dipole antenna wasused, replacing the handset to reduce the weight and toensure a setup with small exposure variance from testuser to test user. Any typical size handset radiating at theTETRA frequencies at 420 MHz used in this study will

Fig. 1. A test person situated in the exposure room with theequipment used for conducting the test. On the walls radio-waveabsorbers are used to avoid reflections and to further shieldfieldsfromoutside theroom.

382 Riddervold et al.

Bioelectromagnetics

act as an asymmetrical dipole antenna and, therefore,the smaller length dipole antenna was selected to fita typical handset exposure, whereas the meander typewas used to keep antenna matching to an optimum(see Fig. 4).

For this experiment, we placed the meanderantenna in the ‘cheek’ position as defined in IEC/EN[2006] to ensure repeatability and to allow forcomparison with SAR measurement on a liquidphantom. The ‘cheek’ arrangement, together with

setting the peak spatial-average SAR value to the upperlimit imposed by current guidelines, also representsthe worst-case scenario because the antenna is broughtas close as possible to the brain area. The SARdistributions in the phantom obtained numerically forboth the meander antenna and a simple model ofhandset were very similar, with highest SAR in thetissue-simulating liquid close to the antenna andmonotonically decreasing with distance. Small differ-ences observed in the distributions (e.g., the locations of

Fig. 2. A block diagram of the instrumentations for the exposure setup. A handheld phone is usedto generate the Tetra exposure. The signal is taken via the external coaxial output on the phoneand the level is regulated byan amplifierandvariable attenuators.The spectrumanalyzer (AgilentTechnologies,Santa Clara,CA) is used to constantlymonitor the signal to the exposure antenna inthe test roomandmeasureany signal inside the test room to ensureno unwantedexposure duringthe test.

Bioelectromagnetics

TETRAPortables and Cognitive Performance 383

the peak SAR averaging volumes differed by 8 mm) are,nevertheless, expected when using different handsetsand/or different holding positions. This uncertainty isalso reflected by the standard [IEC/EN, 2006] in that itdefines limits only on SAR peak spatial-averagedvalues without regard to its distribution. Therefore, inthis study we focused on correct setting of the peakspatial-average SAR, and utilized the meander antennato minimize SAR variations across the participants andin possible future repeated studies.

The meander dipole exposure antenna wasattached to the participants’ head so that no hands wererequired to hold the antenna in the proper position. Thephone was not in direct contact with skin as describedbelow. The exposure antenna was placed on the left sideof the head of the participants (left-sided exposure), andthe device was positioned on the cheek. Because havingan actual conversation over the TETRA phone couldaffect the participant’s mental condition or physiolog-ical function, the experiment was conducted withoutconversation.

The influence of the distance of the exposureantenna from the head was studied by means ofnumerical experiments using the finite-differencetime-domain (FDTD) method [Taflove, 2005]. Theresolution of the spatial grid (corresponding to the sizeof one FDTD cube cell) chosen for this initial

investigation was 5 mm (isotropic) to save resourceswhen computing multiple runs with various parameters.

The simulation setup is shown in Figure 5. Thehuman torso was represented by a generic homoge-neous phantom with shell thickness corresponding to 1FDTD cell (5 mm) made of lossless material withrelative permittivity 4.6. The phantom was filled withliquid of relative permittivity 43.8 and conductivity0.85. The antenna in this setup was 145 mm long and15 mm wide with symmetric feeding (see Fig. 4). Theposition of the antenna was, because of FDTD meshorthogonality, horizontal along the side of the head,approximating the talk mode angle of 60 degrees to thevertical axis. A metallic wire simulating the feedingcoaxial cable was arranged to the path expected for theexposure setup, originating near the center of the dipoleand perpendicular to it, making a loop to the top of thehead and finally following the back of the phantom at afixed gap.

The antenna was positioned at various distancesfrom the phantom head and the resulting peak averagedSAR was observed (Table 1). The gap between thefeeding coaxial cable and the phantom was initially5 mm, both at the top of the head and at the back;however, slightly wider gaps were also tried. As shownin Table 1, the peak averaged SAR varies considerablywith the antenna distance from the head, monotonicallydecreasing in accordance with theory. On the otherhand, the influence of the gap between the feeder andthe phantom was negligible, indicating that the amountof energy propagating along the feeding cable back tothe generator was very small.

The target SAR in the experiment was set to thegeneral public exposure limit according to ICNIRPguidelines [ICNIRP, 1998] and IEEE C95.1 standard[IEEE, 2005], that is 2 W/kg averaged over 10 g oftissue. Hence, for the given exposure setup it wasnecessary to determine the correct input power thatwould produce the desired SAR value. This was

Fig. 3. Fixing of the test antenna on a mannequin. The exposureantennaismountedontheleft sideoftheheadandheldbyaplastichelmet (the black plastic).The feeding cable can be seen from theexposure antenna going toward the top of the head and guideddownthebackof themannequin.

Fig. 4. The exposure antenna made on FR4 material as ameandereddipoleantenna.Thehole in the PCBisused topositionthe exposure antenna and the hole is collocated with the ear.In the center, theendof thesmallcoaxialcable canbeseen.

Fig. 5. Simulatedgenericphantomwithmeanderantennain5mmresolution.Right: feedingcoaxialcableonthebackofthephantom.

384 Riddervold et al.

Bioelectromagnetics

accomplished both by measurements on a liquidphantom and by high-resolution simulation.

The SAR was measured using the DASY4dosimetric assessment system (Schmid and PartnerEngineering AG, Munich, Germany) at IMST GmbH,Germany. The phantom was a twin-SAM basin filledwith tissue-simulating liquid of relative permittivity43.8, conductivity 0.85 S/m and mass density 1,000 kg/m3. The input signal was a continuous wave at420 MHz, with 27 dBm power. The SAR was calculatedfrom measured field values obtained by an isotropicE-field probe scanning in a volume grid of 5 mmresolution. The resulting peak spatial-averageSAR values are: 1.73 (1 g-averaged) and 1.26 W/kg(10 g-averaged).

In the case of simulation, the spatial resolution ofthe FDTD method was set to 1 mm to achieve sufficientaccuracy of the results. The head phantom was thespecific anthropomorphic mannequin (SAM) definedby IEC/EN 62209 [IEC/EN, 2006], identical to the oneused for the SAR measurement. The parameters of thetissue-simulating liquid also corresponded with thoseused in the SAR measurement. The simulation setup isshown in Figure 6. The relative permittivity and losstangent (evaluated at 420 MHz) of the exposure antennasubstrate were set to 4.5 and 0.008, respectively,

modeling an FR4 substrate. The metallic strips wereconsidered lossless and were substituted by a perfectelectric conductor in the FDTD method.

The foam support of the antenna, which was usedduring the exposure study and SAR measurement tokeep stable distance of the antenna from the head,(see Fig. 3) was omitted in the simulations because thepermittivity of the foam is very close to air [Westphaland Sils, 1975].

The antenna was excited by the localizedsymmetric source, but the feeding cable was includedin the simulation (bold black line in Fig. 6) and took thesame position as in the SAR measurement: from theantenna feeding point bent toward the top of the head,then led along the back to the neck, in 2 cm distance, andfinally departing on the same side where the antennawas attached.

The computed peak spatial-average SAR valuesare 2.18 (1 g-averaged) and 1.61 W/kg (10 g-averaged),for 27 dBm input power. These values are only about1 dB higher than the measurement results; the differ-ence is likely due to the presence of loss in the plasticof the helmet and the connecting cable used in themeasurement.

For the exposure, a power value of 34.6 dBm to theexposure antenna was used, which corresponds to apeak SAR value of 2 W/kg (10 g-averaged). The powerlevel of 34.6 dBm is obtained from the measured SARvalue of 1.26 W/kg for an input power of 27 dBm(0.5 W) scaled to 2.0 W/kg, times the TDMA factor forthe TETRA phone of 3.6 (burst-on vs. -off time),In detail, the power value was calculated in this way:2.0/1.26� 0.5W� 3.6¼ 2.86 W or 34.6 dBm.

Cognitive Tests

A battery of four standardized cognitive tests withestablished utility in neuropsychological assessmentwas used. The tests were selected for previously shownclinical sensitivity to subtle cognitive deterioration,

TABLE 1. Averaged SAR Values for Various Distances of the Meander Antenna From theHead; Pin¼ 1 W

Antenna distance(mm)

SAR 1 g(W/kg)

SAR 10 g(W/kg) Feeding cable position

5 7.97 6.05 Basic case:10 6.67 5.22 5 mm from the back,15 5.64 4.51 5 mm above the top of the head20 4.76 3.8725 3.99 3.330 3.33 2.7835 2.77 2.345 7.98 6.06 10 mm from the back

20 4.81 3.9120 4.75 3.87 10 mm above the top of the head

Fig. 6. FDTD simulationof the exposure setup: meanderantenna,feedingcableand the SAMphantom,1mmresolution.

TETRAPortables and Cognitive Performance 385

Bioelectromagnetics

practical usability in the climate chamber and ability toassess across general cognitive abilities (reaction time,psycho-motor speed, attention, verbal and visuo-spatialworking memory, and executive function) in a relativelyshort period of time. The following tests were used:two tests from the computer-administered CambridgeNeuropsychological Test Automated Battery (CAN-TAB eclipseTM), Reaction Time (RTI) and Spatial Span(SSP). In addition, Wechsler Adult Intelligence Scale-Third Edition (WAIS-III), subtest Digit Span (DSP) andfinally TMB. The tests were administered and scored bytrained personnel under supervision by a registeredsenior specialist in clinical neuropsychology.

In the CANTAB tests, the participants wereinstructed to respond to stimuli presented on a computerscreen by pressing a specific button on a pressure pad ortouch screen as accurately as possible. Each exposuresession started with 5 min exposure before the testingwas initiated.

CANTAB RTI was used to evaluate simple andfive-choice reaction time. Participants had to hold thepressure pad down, then release it and touch the screenas quickly as possible when a yellow dot appeared in acircle. Thereby RTI measured the participant’s speedof response to a visual target (reaction and movementtime).

CANTAB SSP, which is a computerized versionof the Corsi block-tapping test, assesses visuo-spatialworking memory by measuring the longest sequencesuccessfully recalled by the participant. White squareswere shown, some of which briefly changed color in avariable sequence. Afterward, the participant had totouch the boxes, which had changed color in the sameorder that they were displayed by the computer (forclinical mode) or in the reverse order (for reversemode). The number of boxes increased from 2 atthe beginning of the test to 9 at the end, and the sequenceand color varied throughout the test. Both forward andbackward span were measured. After completing thefirst test, the participant was automatically given thenext, thereby completing the tasks in 10–20 min.Parallel mode (if available for the specific task) wasused for repeated testing to ensure that the order andpatterns are displayed differently at each test sectionto minimize learning effect.

After completion of the computer-based tests,TMB was administered. Note that TMB has a lowspecificity to identify which specific cognitive domainthat is possibly impaired because its performancerequires multiple cognitive domains (psycho-motorspeed, attention and executive function). For ourpurpose, however, high sensitivity is critical. TMB isone of the most frequently used tests in neuropsycho-logical research and clinical evaluations worldwide and

is a well-established test with high sensitivity to evenmild cognitive deterioration [Lezak et al., 2004;Tombaugh, 2004]. It was, therefore, chosen as theprimary outcome measure. TMB was initiated after35 min of exposure. In TMB, the participant had todraw lines alternating between numbers and letters inconsecutive order. The same test was used in eachsession and performance was assessed by the time takento complete the trial correctly. There are alternativeforms of errors during task completion that requireimmediate correction and performance is measured asthe speed at which the task is correctly completed[Keetley et al., 2001].

WAIS DSP is one of the most commonly usedmeasures of immediate verbal recall, attention spanand verbal working memory in neuropsychologicalresearch and clinical evaluations. This test consisted oftwo tasks administered independently: Digits Forwardand Digits Backward. For Digits Forward, the testadminister reads a series of digit sequences to theparticipant who is required to repeat the sequences inthe same order as presented. For Digits Backward,the participant is required to repeat the sequences inreverse order. Digits are presented at about the rate ofone per second. The sequences began with two digits,increasing until the participant committed an error orreached a sequence of nine digits. Reverse repetition ismore difficult and requires more processes besidesimmediate recall.

Subjective Symptoms

A computer-administered questionnaire was usedto assess self-reported subjective symptoms. Thequestionnaire was completed prior to (baseline) and atthe end of each exposure session. Each question waspresented on a computer touch screen. Participantswere asked to rate the perceived strength of eachsymptom question on a Visual Analogue Scale (VAS)ranging from ‘not at all’ (0) to ‘very much’ (202 mm).The intensity of any discomfort was registered as thelength in millimeter from the left end of the scale to themarker. The evaluations were registered as percentfull scale subtracted from the pre-exposure baselinesetting. Increasing values generally meant increasingdiscomfort.

The questionnaire included four control itemsconcerning the exposure, air quality, humidity andtemperature, and 11 items concerned with symptoms,for example concentration difficulties, tingling or pain,headache, nausea, dizziness and claustrophobia. Thisstudy focused a priori on ‘headache’ and ‘concentrationdifficulties’ as secondary hypotheses, as these symp-toms could trigger the remaining symptoms. All tests,including the instructions and computer-based ques-

386 Riddervold et al.

Bioelectromagnetics

tionnaire, were presented in one practice session beforeactual testing. Each outcome was measured as anabsolute change from baseline to end of the session.

Analysis

The statistical analysis was planned prior tothe study and blinding was maintained until after thepreliminary analyses had been completed. Data entrieswere performed in duplicate independently by tworesearch assistants and stored on a laptop computer.

For the variables, TMB, RTI (complex RTI) andRTI (complex movement time) times were measured,and the log-transformed data were analyzed with anANOVA model including study day and exposureas fixed factors and participants as a random factor.These variables are described by the geometric mean,coefficient of variance (CV), relative differencebetween exposures including 95% confidence interval(CI), and P-value.

Because of ceiling and flooring problems in thedata, heterogeneity in the (within participant) variationor violations of the assumption of normally distributeddata, it was not appropriate to analyze the data of theremaining outcomes ‘SSP’, ‘DSP’, ‘Headache’ (changefrom baseline) and ‘Concentration difficulties’ (changefrom baseline) with ANOVAs. To compare shamexposure and TETRA signal exposure, and taking intoaccount a possible ‘learning effect’, we analyzed thedata by a standard technique taking into account thedesign (cross-over). The participants were dividedinto two groups because of the two possible exposureorders; one group of participants were exposed to shamexposure before the TETRA signal exposure andanother group of participants were exposed to TETRAsignal before the sham exposure. The hypothesis of no

difference between sham and TETRA signal exposurewas then tested by comparing the two groups withrespect to the differences between the first andthe second measurement. A Wilcoxon rank sum testwas used to compare the two groups. In a similar way,we tested the hypothesis of ‘no effect of learning’.

Subjective symptoms at baseline are described bythe median and the interquartile range. The data for‘change in headache’ and ‘change in concentration’for both exposures and the difference between thetwo exposures are described by box-plots. The upperadjacent value in the plots is the largest data pointsmaller than 75th percentile plus 3/2 times theinterquartile range. The lower adjacent value is definedin a similar way.

Based on a within-subject coefficient variationof 10% in the TMB test [Tombaugh, 2004] and anexpected 5% observed change in the mean, it wascalculated that a group size of 55 persons would yieldthe optimal statistical power of approximately 95%.Based on the relation between number of participantsand power, this was the optimal point on the curve froma cost-effectiveness point of view. To ensure balance inthe randomization, it was decided to include 56 personsin the study. However, only 53 completed all sessionsand measures.

RESULTS

Baseline symptoms and perception status arelisted in Table 2. Only minor differences between thetwo exposure groups were observed.

The results for our primary outcome (the TMBtest) are shown in Table 3. The estimated differencebetween the TETRA exposure and sham exposure

TABLE 2. Subjective Symptoms Rated at Baseline on a Visual Analogue Scale (VAS) in Proportion to Maximum and AreDescribed by the Median and Interquartile Range (IqR, Inter quartile range)

Rated variable

Endpoint TETRA exposure Sham exposure

Left Right Median IqR Median IqR

Air temperature Annoying cold Annoying hot 0.51 (0.49–0.52) 0.50 (0.49–0.52)Air humidity Annoying dry Annoying humid 0.50 (0.43–0.52) 0.51 (0.50–0.53)Air quality Pleasant Annoying unpleasant 0.04 (0.01–0.27) 0.04 (0.01–0.20)Sweating Not at all Very much 0.04 (0.01–0.20) 0.04 (0.01–0.18)Freezing Not at all Very much 0.03 (0.01–0.07) 0.02 (0.01–0.17)Breathlessness Not at all Very much 0.02 (0.00–0.03) 0.01 (0.01–0.03)Tingling Not at all Very much 0.02 (0.01–0.04) 0.01 (0.00–0.03)Pain Not at all Very much 0.02 (0.00–0.03) 0.02 (0.00–0.03)Sleepiness Not at all Very much 0.03 (0.01–0.09) 0.03 (0.01–0.07)Nausea Not at all Very much 0.01 (0.00–0.03) 0.01 (0.00–0.03)Dizziness Not at all Very much 0.02 (0.01–0.03) 0.02 (0.00–0.03)Headache Not at all Very much 0.01 (0.00–0.03) 0.01 (0.00–0.03)Concentration difficulties Not at all Very much 0.02 (0.01–0.05) 0.02 (0.01–0.04)

TETRAPortables and Cognitive Performance 387

Bioelectromagnetics

was 3.8% (�1.6% to 9.2%) which did not reachstatistical significance (P¼ 0.16). We found a signifi-cant (P< 0.001) effect of learning and the estimatedimprovement from day 1 to 2 was 15.3% (10.0% to20.7%). The standard deviation of the relative differ-ence between the TETRA and sham exposure wasestimated to be 13.7%.

The result of the RTI Five-Choice test (reactionand movement time) is shown in Table 3, and the resultsof the remaining secondary outcomes are presented inFigures 7 and 8. The difference between the TETRAsignal, compared to the sham exposure, did not reachstatistical significance for any of the cognitive out-comes, including ‘RTI reaction time’ (P¼ 0.078),‘RTI movement time’ (P¼ 0.41), SSP (P¼ 0.77),DSP (P¼ 0.37), change from pre- to post-exposureof ‘headache’ symptoms (P¼ 0.68) or change in‘concentration difficulties’ (P¼ 0.17). We found asignificant effect of learning in both SSP (P¼ 0.011)and DSP (P¼ 0.005). No significant effects of learningwere observed for ‘RTI reaction time’ (P¼ 0.41), ‘RTImovement time’ (P¼ 0.50), or in change from pre- topost-exposure of ‘headache’ symptoms (P¼ 0.81) andof ‘concentration difficulties’ (P¼ 0.24).

DISCUSSION

Compared with sham conditions, a 45-mincontinuous exposure to TETRA RF had no statistically

significant effects on cognitive performance or on self-reported perception of symptoms in normal healthymales in the present study. We did, however, observe asignificant effect of learning in several of the cognitivetasks.

In controlled experiments, it is generally acceptedthat the double-blinded, randomized and outbalanceddesign is a powerful method to reduce the possibleconfounders. In this study, the blinding worked asintended. After exposure to TETRA, 16 of 53 parti-cipants answered ‘yes’ to the question ‘do you think thatyou have been exposed to electromagnetic radiation?’After sham exposure, 18 of 53 participants answered‘yes’ to the same question. On this basis, we state thatthe participants were not aware if they were exposedor not.

Several studies have been published on the effectof EMF from mobile phones on human volunteers.Previous research within this field has been criticizedfor using inadequate methodological design (lack ofblinding techniques, randomization or counter-balanc-ing of conditions and participants), arbitrary selectionof cognitive tests, highly variable EMF parameters(frequency, power and distance to EMF source) andinsufficient statistical methods.

We have tried to address these methodologicalconcerns in the present study. The blinding of theexposure system was performed so that neither theinvestigator nor the participants were aware of whichexposure they were subjected to. Furthermore, theoperator of the system was unable to interfere with thenature of the exposure of each participant, the systemsettings or any variation in the dependent variables. Toavoid the risk that extremely low frequency (ELF)

TABLE 3. Cognitive Performance Measured by Trail Making B, Reaction Time and Movement Time in the RTI test

Outcome group

TETRA Sham TETRA vs. Sham

gm (s) CV (%) gm (s) CV (%) rd (%) 95% CI P-value

Trail making B 54.0 25 52.0 29 3.8 �1.6 to �9.2 0.16RTI reaction time 322.0 12 316.0 11 1.9 �0.2 to �3.9 0.08RTI movement time 341.0 24 334.0 25 1.0 �2.5 to �6.0 0.41

Outcomes are described by the geometric mean (gm), confidence variance (CV), relative difference (rd) between exposures, including 95%confidence interval (CI) and P-value.

Fig. 7. Box plots for ‘Change in headache’and Change in concen-tration from baseline measured from the absolute change on theVisual AnalogueScale.

Fig. 8. Box plot illustrating the differences between TETRAand sham exposures for ‘change in headache’ and ‘change inconcentration’.

388 Riddervold et al.

Bioelectromagnetics

exposure from the batteries in the handset couldinterfere with the TETRA signal, a dummy TETRAphone without batteries was used for exposure. Forcognitive testing, we selected only well-known teststo examine very specific components of cognition.Furthermore, the computerized neuropsychologicaltests in the CANTAB1 are sensitive and extensivelyvalidated. Finally, the exposure was conducted in aclimate chamber to reduce other EMF sources thatconfound the exposure and to secure constant environ-mental conditions throughout the experiment. We thuseffectively eliminated the methodological sources oferror for which most other studies have been criticized.

Many experimental provocation studies have beenconducted since the question of increased health riskfrom exposure to communication system-related EMFwas first raised. Our results on symptom rating do notsupport the hypothesis that exposure to communicationsystems’ RF fields produces subjective effects suchas headache or concentration difficulties. This isin agreement with the results of previous studies[Koivisto et al., 2001; Wilen et al., 2006; Riddervoldet al., 2008]. Furthermore, in correspondence withresults from exposure studies concerning possibleeffects on cognition in relation to EMF exposure, wefound no effects on cognitive functions [Eliyahu et al.,2006; Nam et al., 2006; Haarala et al., 2007].

The hand-held TETRA devices can be held to theear like a mobile phone, or they can be used in adispatcher-style in front of the face, or mountedremotely on the shoulder or abdomen [Dimbylowet al., 2003]. However, as the last three options areexpected to yield much lower SAR values in the head,we only investigated the mobile phone-like position toachieve the highest possible EMF exposure to the brainbecause the possible health concern in question wascognitive functions and symptoms.

Modulation has been a factor in the public healthcontroversy. A commentary from 2004 by Foster andRepacholi extensively discussed the mechanisms ofmodulation as a factor of potential importance inassessment of risk of RF energy emitted by communi-cation systems and other technologies. They alsodiscussed the variation and complexity of modulationproperties, frequency and other exposure parametersfor these communication signals, which complicatesthe research within this field because of the ongoingdevelopment and implementation of new technologiesand communication systems. Furthermore, they arguedthat the modulation concern requires additionalresearch to understand mechanisms of the possiblebiological effects [Foster and Repacholi, 2004].

Assessment of specific energy absorption rates(SAR) in the head from TETRA handset has previously

been performed by Dimbylow et al. [2003]. To assessand document the given exposure, we measured thedistribution of SAR in an anatomically realistic modelof the head from the representative portable TETRAdevice using the FDTD method.

In general, our results did not confirm our primaryhypothesis that EMF radiation from portable TETRAdevices reduces general performance in the TMB test.Multiple comparisons in our secondary outcomeswould only work toward inflating Type I error, and sowould not affect the conclusions drawn in the paper. Inthe present study, we only assessed the acute effect ofshort-term exposure from TETRA handsets and it is,therefore, not possible to draw any conclusions aboutpossible effects from long-term exposure. The TETRAcommunication system is expected to be widelydeployed for use by staff in emergency services. Thisrelatively stable workforce with well-defined workpatterns could serve as a study population in futureepidemiological studies examining working practicesand conditions of exposure to RF from TETRAsystems.

Very limited information on possible adversehealth effects is available on exposures from hand-heldTETRA devices. Further research is needed to providemore information on exposures from these devices andfrom any other transmitting equipment deployed foruse. The lack of consistent evidence that pulsed orcontinuous wave (CW) exposure at power and frequen-cies related to mobile communication systems ques-tions their possible effects on neurophysiology andhuman behavior.

REFERENCES

Challis LJ. 2005. Mechanisms for interaction between RF fieldsand biological tissue. Bioelectromagnetics 26(Suppl. 7):S98–S106.

Cook CM, Thomas AW, Prato FS. 2002. Human electrophysio-logical and cognitive effects of exposure to ELF magneticand ELF modulated RF and microwave fields: A review ofrecent studies. Bioelectromagnetics 23(2):144–157.

Cook CM, Saucier DM, Thomas AW, Prato FS. 2006. Exposureto ELF magnetic and ELF-modulated radiofrequency fields:The time course of physiological and cognitive effectsobserved in recent studies (2001–2005). Bioelectromag-netics 27:613–627.

Dimbylow P, Khalid M, Mann S. 2003. Assessment of specificenergy absorption rate (SAR) in the head from a TETRAhandset. Phys Med Biol 48:3911–3926.

Edelstyn N, Oldershaw A. 2002. The acute effects of exposure to theelectromagnetic field emitted by mobile phones on humanattention. Neuroreport 13(1):119–121.

Eliyahu I, Luria R, Hareuveny R, Margaliot M, Meiran N, Shani G.2006. Effects of radiofrequency radiation emitted by cellulartelephones on cognitive functions of humans. Bioelectro-magnetics 27:119–126.

TETRAPortables and Cognitive Performance 389

Bioelectromagnetics

ETSI. 2009. Terrestrial trunked radio (TETRA): Description by theEuropean Telecommunications Standards Institute (ETSI).Available at: www.etsi.org/website/Technologies/TETRA.aspx (last accessed 15 December 2009).

Foster KR, Repacholi MH. 2004. Biological effects of radio-frequency fields: Does modulation matter? Radiat Res 162:219–225.

Gade A, Mortensen EL. 1984. The influence of age, education, andintelligence on neuropsychological test performance. Paperpresented at the 3rd Nordic Conference in BehaviourToxicology, Aarhus, Denmark.

Haarala C, Takio F, Rintee T, Laine M, Koivisto M, Revonsuo A,Hamalainen H. 2007. Pulsed and continuous wave mobilephone exposure over left versus right hemisphere: Effects onhuman cognitive function. Bioelectromagnetics 28:289–295.

Hossmann KA, Hermann DM. 2003. Effects of electromagneticradiation of mobile phones on the central nervous system.Bioelectromagnetics 24:49–62.

IEC/EN. 2006. Human exposure to radio frequency fields fromhand-held and body-mounted wireless communicationdevices—human models, instrumentation, and procedures,IEC/EN Standard 62209.

IEEE. 2005. IEEE standard for safety levels with respect to humanexposure to radio frequency electromagnetic fields, 3 kHz–300 GHz. IEEE Standard C95:1.

International Commission on Non-Ionizing Radiation Protection(ICNIRP). 1998. Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to300 GHz). Health Phys 74(4):494–522. Available at: http://www.icnirp.de/documents/emfgdl.pdf.

Keetley V, Wood A, Sadafi H, Stough C. 2001. Neuropsychologicalsequelae of 50 Hz magnetic fields. Int J Radiat Biol 77(6):735–742.

Koivisto M, Revonsuo A, Krause C, Haarala C, Sillanmaki L, LaineM, Hamalainen H. 2000a. Effects of 902 MHz electromagneticfield emitted by cellular telephones on response times inhumans. Cogn Neurosci Neuropsychol 11(2):413–415.

Koivisto M, Krause CM, Revonsuo A, Laine M, Hamalainen H.2000b. The effects of electromagnetic field emitted by GSMphones on working memory. Neuroreport 11(8):1641–1643.

Koivisto M, Haarala C, Krause CM, Revonsuo A, Laine M,Hamalainen H. 2001. GSM phone signal does not producesubjective symptoms. Bioelectromagnetics 22:212–215.

Lezak MD, Howieson DB, Loring DW. 2004. Neuropsychologicalassessment 4th edition, Oxford: Oxford University Press.

Nam KC, Kim SW, Kim SC, Kim DW. 2006. Effects of RF exposureof teenagers and adults by CDMA cellular phones.Bioelectromagnetics 27:509–514.

NRPB. 2001. Possible health effects from terrestrial trunked radio(TETRA): Report of an independent Advisory Group onNon-ionising Radiation. Document of the NRPB: Volume 12,No. 2. Available online at: http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1194947336937.

Pedersen GF, Tartiere M, Knudsen MB. 2000. Radiation efficiencyof handheld phones. Vehicular Technology ConferenceProceedings, IEEE 51st VTC 2000-Spring Tokyo, vol 2 page1381–1385.

Pelosi M, Franek O, Knudsen MB, Christensen M, Pedersen GF.2009. A grip study for talk and data modes in mobile phones.IEEE Trans Ant Prop 57(4):856–865.

Preece AW, Iwi G, Davies-Schmidt A, Wesnes K, Butler S, Lim E,Varey A. 1999. Effect of a 915-MHz simulated mobile phonesignal on cognitive function in man. Int J Radiat Biol 75(4):447–456.

Riddervold IS, Pedersen GF, Andersen NT, Pedersen AD, AndersenJB, Zachariae R, Mølhave L, Sigsgaard T, Kjærgaard SK.2008. Cognitive function and symptoms in adults andadolescents in relation to RF radiation from UMTS basestations. Bioelectromagnetics 29:257–267.

Scientific Committee on Emerging and Newly Identified HealthRisks (SCENIHR). 2009. Health Effects on Exposureto EMF. European Commission 2009. DG Health andConsumer Protection. Brussels, Belgium.

Sienkiewicz Z, Jones N, Bottomley A. 2005. Neurobehaviouraleffects of electromagnetic fields. Bioelectromagnetics26(Suppl. 7):S116–S126.

Smythe JW, Costall B. 2003. Mobile phone use facilitates memoryin male, but not female, subjects. Neuroreport 14(2):243–246.

Taflove A, editor. 2005. Computational electrodynamics: TheFinite-difference time-domain method 3rd edition. Nor-wood, MA: Artech House.

Tombaugh TN. 2004. Trail Making Test A and B: Normative datastratified by age and education. Arch Clin Neuropsychol19:203–214.

Valentini E, Curcio G, Moroni F, Ferrara M, De Gennaro L, BertiniM. 2007. Neurophysiological effects of mobile phoneelectromagnetic fields on humans: A comprehensive review.Bioelectromagnetics 28:415–432.

Warrington EK. 1984. Recognition memory test. UK: Windsor.Westphal WB, Sils A. 1975. Dielectric constant and loss data,

AFML-TR-74-250 Part II, Dec. 1975.Wilen J, Johansson A, Kalezic N, Lyskov E, Sandstrom M. 2006.

Psychophysiological tests and provocation of subjects withmobile phone related symptoms. Bioelectromagnetics 27:204–214.

390 Riddervold et al.

Bioelectromagnetics