Does exposure to GSM 900 MHz mobile phone radiation affect short-term memory of elementary school students?

BACKGROUND: Now-a-days, children are exposed to mobile phone radiation at a very early age. We have previously shown that a large proportion of children in the city of Shiraz, Iran use mobile phones. Furthermore, we have indicated that the visual reaction time (VRT) of university students was significantly affected by a 10 min real/sham exposure to electromagnetic fields emitted by mobile phone. We found that these exposures decreased the reaction time which might lead to a better response to different hazards. We have also revealed that occupational exposures to radar radiations decreased the reaction time in radar workers. The purpose of this study was to investigate whether short-term exposure of elementary school students to radiofrequency (RF) radiation leads to changes in their reaction time and short-term memory.
MATERIALS AND METHODS: A total of 60 elementary school children ages ranging from 8 to 10 years studying at a public elementary school in Shiraz, Iran were enrolled in this study. Standardized computer-based tests of VRT and short-term memory (modified for children) were administered. The students were asked to perform some preliminary tests for orientation with the VRT test. After orientation, to reduce the random variation of measurements, each test was repeated ten times in both real and sham exposure phases. The time interval between the two subsequent sham and real exposure phases was 30 min.
RESULTS: The mean ± standard deviation reaction times after a 10 min talk period and after a 10 min sham exposure (switched off mobile) period were 249.0 ± 82.3 ms and 252.9 ± 68.2 ms (P = 0.629), respectively. On the other hand, the mean short-term memory scores after the talk and sham exposure periods were 1062.60 ± 305.39, and 1003.84 ± 339.68 (P = 0.030), respectively.
CONCLUSION: To the best of our knowledge, this is the first study to show that short-term exposure of elementary school students to RF radiation leads to the better performance of their short-term memory.

Introduction

Now-a-days, children are exposed to mobile phone radiation at a very early age. There is a rapidly growing concern about the possible health effects of radiofrequency (RF) radiation emitted by mobile phones on children's health. The potentially greater susceptibility of children's developing nervous systems, higher conductivity of their brain tissue, greater RF penetration due to their head size, and finally the fact that children have a longer lifetime exposure than adults are among the rational for these concerns.[1] Moreover, it has been reported that the specific absorption rate (SAR) of RF radiation in the children's brain is higher than that of the adults. Differences in the size, shape, water content and tissue distribution of the brain in children are believed to be responsible for the higher SAR and vulnerability of children. On the other hand, the issue of children carrying mobile phones in schools and using these communicational devices during instructional time is another important concern. In the Islamic Republic of Iran, the use of mobile phone in schools is banned. However, similar to other countries in some schools the policies regarding mobile phone use are being somehow relaxed.[2] In a report published in 2011, we have shown that a large proportion of children in the city of Shiraz, Iran use mobile phones. We also indicated a significant increase in some self-reported symptoms among children who use mobile phones.[2]

Reaction time plays a critical role in performing activities necessary to cope better with life's threats and/or avoid hazards. Reaction time widely varies from one individual to another, and increased reaction time may lead to fatal accidents. We and other investigators have previously studied the effects of exposure to electromagnetic fields (EMF) on reaction time.[34567] Previously, we have indicated that the visual reaction time (VRT) of university students was significantly affected by a 10 min real/sham exposure to EMF emitted by mobile phone.[7] We found that these exposures caused decreased reaction time, which might lead to a better response to different hazards. We have previously also shown that occupational exposures to radar radiations decreased reaction time in radar workers.[8] Over the past years, our laboratory has focused on studying the health effects of exposure of laboratory animals and humans to some common and/or occupational sources of EMF such as mobile phones[7891011121314] and their base stations,[15] mobile phone jammers,[16] laptop computers,[17] radars,[8] dentistry cavitrons[18] and MRI.[1319] The purpose of this study was to investigate whether short-term exposure of elementary school students to RF radiation leads to changes in their reaction time and short-term memory.

Materials and Methods

In this study, sixty male elementary school children, in the age group of 7-10-year-old at a boys’ public elementary school in Shiraz, Iran were the subjects of the study. The purpose of the study was explained to the students and teachers, and a letter explaining the goal of the study and consent form were sent to the children's parents. The study was approved by the Ethics Committee of the Shiraz University of Medical Sciences. Left-handed students were excluded from the study. Computer-assisted-tests of VRT and short-term memory (modified for children) were administered. Reaction time is usually defined as the time interval between exposure to a stimulus and detection of a response; in the present study, it was the amount of time it took an individual to physically respond to the visual stimulus on the display of a laptop computer. The students were asked to perform some preliminary tests for orientation with the VRT test. After orientation, to reduce random variation of measurements, each test was repeated ten times in both real and sham exposure phases. The students’ VRT was recorded with a simple blind computer assisted-test, before and after a 10 min real/sham exposure to EMF of mobile phone. The reason for choosing 10 min intervals for either real exposures or sham exposures was the point that based on our previous studies,[2] only about 16% of the male and 11% of the female students had daily call time longer than 10 min. In this light, a 10 min exposure could represent a common condition. Participants were asked to sit in an armchair in front of an ergonomic liquid-crystal display monitor. The time interval between the two subsequent sham and real exposure phases was 30 min. A GSM Huawei G5520 mobile phone (Huawei Technologies Co. Ltd., China) was used for exposure to microwaves. According to manufacturer's specifications, the highest SAR value under the ICNIRP guidelines for using this device at the ear was 1.45 W/kg. The phone was in a normal talk mode but as the loudspeaker was disconnected, it did not produce any sound. The students were informed that during the experiment they would be exposed to EMF emitted by mobile phone, but they were not aware of the order of real/sham exposures. The order of the exposures (sham-real or real-sham) was chosen at random for each participant.

Results

The participants’ mean (± standard deviation [SD]) age was 8.81 ± 0.82 (ranged, 7-10) years. The majority of them were between 8 and 9 years of age (74.58%). Among the participants, 10.2% were 1st year students, while 13.6%, 61.0% and 15.2% were 2nd, 3rd and 4th year students. The mean (± SD) reaction time after a 10 min talk period and after a 10 min sham exposure (switched off mobile) period were 249.0 ± 82.3 ms and 252.9 ± 68.2 ms (P = 0.629), respectively [Figure 1]. On the other hand, the mean short-term memory scores after the talk and sham exposure periods were 1062.60 ± 305.39 and 1003.84 ± 339.68 (P = 0.030), respectively [Figure 2].

Figure 1

The mean (± standard deviation) reaction time after a 10 min talk period and after a 10 min sham exposure (switched off mobile) period

Figure 2

The mean short-term memory scores after the talk and sham exposure periods

Discussion

Results obtained in this study showed that a 10 min talk period could not alter the reaction time in elementary school students, while exposures are extending over a short period of time significantly increased the short-term memory scores. To the best of our knowledge, this is the first study to show that short-term exposure of elementary school students to RF radiation leads to the better performance of their short-term memory. These findings, along with our previous reports,[78] rule out the widespread assumption that mobile-emitted-radiations increase the reaction time.

Mortazavi et al. have previously reported some beneficial cognitive effects after human short-term exposure to cell phone radiation. In a report published in 2011, Mortazavi et al. showed that the VRT of university students was significantly affected by a 10 min exposure to EMF emitted by mobile phone.[7] They found that these exposures caused decreased reaction time which might lead to a better response to different hazards. They also revealed that occupational exposure to radar radiations decreased the reaction time in radar workers.[8] Increased brain glucose consumption after exposure to RF radiation, as confirmed by PET studies, may be a potential mechanism in this phenomenon.

Our findings are in line with those published by Vecchio et al. in 2012. In their study, subjects underwent two electroencephalographic sessions separated by 1-week. In both sessions, participants conducted a visual go/no-go task before a 45 min real exposure phase to mobile phone GSM EMF or after a sham exposure phase (no EMF). Results of this study showed less power decrease of widely distributed high-frequency alpha rhythms and faster reaction time while no effect was detected in the sham exposure phase. Vecchio et al. concluded that both the peak amplitude of alpha event-related desynchronization and the reaction time are modulated by the effect of the exposure to EMF of GSM mobile phone on the cortical activity. Furthermore, cognitive beneficial effects of long-term exposure to high-frequency EMF have been indicated by some epidemiologic studies. Using a word interference test, Arns et al. showed that long-term heavy cell phone use resulted in better performance of normal subjects.[20] Moreover, Schüz et al. in 2009 reported that long-term cell phone users B (subscribers of 10 years or more) had a 30-40% decreased risk of hospitalization due to Alzheimer's disease and vascular dementia.[21]

On the other hand, our results contradict those of the previous studies such as that conducted by a group of Australian scientists who investigated the reaction time and accuracy rate data during the auditory oddball task. Their study showed an increased reaction time after the exposure compared to sham-exposure intervals.[22] Our results are also in contrast with those reported in 2006, indicating that exposure to pulsed EMFs produced by mobile phone has no short-term effects on human visuomotor choice reaction time and movement time.[23] In this double-blind study, that was claimed by the authors to be the first study to assess human visuomotor behavior after a short-term exposure to mobile phone-generated radiation, it was shown that a 30 min exposure could not change the reaction time. Our findings are also in contrast with those of a report that was performed on the effect of exposure to mobile phone radiation on the nervous system activity. This study showed that acute exposure to mobile phone radiation could not induce any change in studied indices of brain activity.[24] As each brain hemisphere is dominant for some of our behaviors, in future studies appropriate tests can be performed separately for right and left brain functions to obtain more powerful results. On the other hand, although the SAR value reported in this study (1.45 W/kg) was a manufacturer's reported highest SAR value under the ICNIRP guidelines for using this phone, in future studies energy absorbed by a unit of mass of exposed tissue over a given time of a person who uses a mobile phone can be measured.

Conclusion

To the best of our knowledge, this is the first study to show that short-term exposure of elementary school students to RF radiation leads to the better performance of their short-term memory. This memory enhancing intervention may open new horizons in the treatment of some cognitive impairment problems.