The effect of electromagnetic field emitted by a mobile phone on the inhibitory control of saccades
Introduction
The widespread use of mobile phones has led to growing concerns about their effects on health, and above all, about the potential effects of the electromagnetic fields (EMF) they emit. Accordingly, there is more and more interest in studying the effects of the high-frequency electromagnetic fields (EMF) emitted by mobile phones on the human body, especially the human brain, using various methodologies (Reiser et al., 1995, Freude et al., 1998, Eulitz et al., 1998, Preece et al., 1999, Borbely et al., 1999, Koivisto et al., 2000a, Koivisto et al., 2000b, Huber et al., 2000, Krause et al., 2004, Sandstrom et al., 2001, Croft et al., 2002, Arai et al., 2003; Lee et al., 2001; Haarala et al., 2004, Hamblin et al., 2004, Hamblin et al., 2006, Hinrichs and Heinze, 2004, Maier et al., 2004, Sienkiewicz et al., 2005, Terao et al., 2005, Terao et al., 2006, Terao et al., 2007, Yuasa et al., 2006; Furubayashi et al., 2009; Mizuno et al., 2009).
Though their findings are still controversial, some studies have concluded that mobile phone use may influence cognitive brain functions, especially attention, in humans (Freude et al., 1998, Preece et al., 2005, Lee et al., 2001, Huber et al., 2002, Edelstyn and Oldershaw, 2002, Russo et al., 2006). Visual spatial attention has recently been demonstrated through brain-imaging studies to be controlled by most of the same underlying cortical structures controlling eye movements (e.g., saccades) (e.g., Nobre et al., 1997, Nobre et al., 2000, Büchel et al., 1998, Corbetta et al., 1998, Schall and Thompson, 1999, Mort et al., 2003). We have previously reported that 30 min of mobile phone use has no effect on subject performance on elementary and simple saccade paradigms, such as visually guided saccade, gap saccade and memory-guided saccade tasks (Terao et al., 2007), suggesting that the cortical processing structures responsible for saccades and attention are not affected by exposure to EMF emitted by mobile phones. In this study, we investigated the effects of EMF on oculomotor paradigms, requiring both initiation and inhibition of saccades depending on the behavioral context, which were considered to be more sensitive to the EMF. It was considered important to investigate such tasks, since the ability to initiate a voluntary action, to inhibit an unwanted one, and to postpone an action until the context is appropriate is one of the most important yet fundamental cognitive functions of the brain (Aron et al., 2007).
The aim of the present study was to investigate the effect of EMF emitted by a digital mobile phone on the inhibitory cortical functions of the brain using oculomotor paradigms. Because they require more complex cognitive processing than the elementary tasks employed in our previous study did (Terao et al., 2007), these oculomotor tasks involving inhibitory function were expected to exhibit more susceptibility to any effects of EMF. Oculomotor paradigms are especially useful for this purpose, because they are particularly easy to record and lend themselves to quantification, thereby allowing the precise analysis of control mechanisms (White et al., 1983). Huber et al., 2002, Huber et al., 2005 reported that 30 min of digital mobile phone use induced regional cerebral blood flow (rCBF) changes in the dorsolateral prefrontal cortex on the exposed side. Furthermore, the neural substrate for inhibition is known to include the ventrolateral frontal cortex (Aron and Poldrack, 2006, Aron et al., 2007, Chikazoe et al., 2007, Hodgson et al., 2007). Thus, since many people hold their mobile phones against their heads in a rather anterior position, cognitive tasks involving inhibitory motor control are especially relevant for considering the effects of EMF emitted by mobile phones on brain function. In view of the functions of the cortical regions where rCBF changes were observed, exposure of the brain to EMF emitted by a mobile phone could lead to impairment in working memory (dorsolateral prefrontal cortex) and/or in the inhibitory motor and oculomotor functions (ventrolateral prefrontal cortex).
In this study, we assessed subjects’ performance on four tasks. The antisaccade task that we used has been extensively used elsewhere as a counterpart of the no-go task (Everling and Fischer, 1998). In addition, we used the cued saccade and overlap saccade tasks to investigate inhibitory control under different conditions.
Section snippets
Subjects
Ten normal subjects (3 men, 7 women, age 35.2 ± 7.5 years [mean ± standard deviation], range 24–47 years), all of whom were right-handed, participated in the present study. The subjects gave their written informed consent to the study, which was approved by the Ethics Committee of the University of Tokyo according to the Declaration of Helsinki. None of the participants reported any psychological or neurological disorders or serious head injury, and none of them had used hands-free devices
The effect of EMF and sham exposure on task performance
In all tasks, the superimposed traces of the saccades exhibited no changes that were apparent through visual inspection after real or sham phone exposure. This suggested that, overall, the saccade parameters for each task either did not change after exposure or changed similarly as a result of real and sham exposure. Statistical analyses were performed to confirm these impressions.
Discussion
The present study showed that neither real nor sham exposure to EMF emitted by a mobile phone resulted in a significant change to many of the parameters of saccades in the four relatively complex oculomotor tasks. On the other hand, after EMF or sham exposure, we did observe a slight but significant shortening of latency in the CUED and OL2 tasks, reductions of saccade amplitude in the AS task, and reductions in saccade velocities of the AS, CUED, and OL1 tasks, but the changes were also
Acknowledgements
This work was partly supported by grants from the Committee to Promote Research on the Possible Biological Effects of Electromagnetic Fields, Ministry of Internal Affairs and Communications (MIC), Japan. We are grateful to Dr. Hideki Fukuda for technical assistance.
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