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Title

The effect of mobile phone emitted electromagnetic fields on human brain activity and performance

Author(s)

Hamblin, Denise L.

Abstract

As mobile phone connections approach two billion worldwide and become steadily more available and affordable, demands for scientific studies on the effect of such EMFs on human functioning similarly increase. The current thesis systematically investigated the effects of acute mobile phone exposure on human brain activity and performance using an in-vivo approach. The research question comprised the following parts: First, is human neural function sensitive to acute mobile phone exposure? Second, if so, what processes are affected? Third, if so, do these neural changes affect gross measures of performance or behaviour? A review of the previous literature found that there was some, but not conclusive evidence that mobile phone exposure affects neural function and some aspects of human performance, and that the studies in question required replication with reliable and realistic dosimetry, double-blinding and additional technical tests to ensure that the experimental set-up was free of artefact contamination. A pilot study was conducted to provide an indication of possible future results, assist in the formation of hypotheses for the main study, and highlight what technical issues required attention before the main study could begin. Results of the pilot study indicated that EMFs emitted by GSM900 mobile phones may alter human brain activity during an auditory task, particularly in proximity to the phone. Both early sensory and later more cognitive ERP components were significantly altered during active compared to sham exposure. Results also suggested that mobile phone exposure may hinder human performance, with longer RTs during the active exposure relative to the sham exposure. However, due to the small sample size of the pilot investigation and questions remaining as to possible technical limitations of the study, these results were treated with caution and used primarily in the formation of future hypotheses for the larger experimental study. Subsequent technical tests provided improvement and validation of the experimental set-up and exposure delivery system, and ensured that future research would be free from such technical limitations. These tests included the characterisation of spectral emissions by the test phone; ensuring that EMFs emitted by the test phones would not interfere with, nor distort, data from the response pad or that processed by the electrode leads; determining whether electrode leads cause an increase or decrease in SAR; and examining the issue of experimenter interference. These tests enabled the conclusion that a positive finding from the large experimental trial would be due to the active exposure of the mobile phone, or in the case of a null finding, would not be due to insufficient or unreliable exposure. Applying the knowledge gained from these technical tests, the main study aimed to provide results of a definitive nature by employing a sample size of 120 sufficient statistical power to detect relatively subtle effects, and a stringent methodological design to account for past limitations. The main study also increased the scope of investigation beyond that achieved in previous research by including endpoints related to sensory processing (auditory and visual tasks), higher cognitive processing (cardsorting task), performance (reaction time and accuracy) and cortical activation (EEG alpha power). To increase this scope even further, within these tasks, the study used data from each scalp electrode and offered insights into the effect of laterality (ipsi- versus contralateral in relation to the exposure source), psychological arousal, perception of transmission, and between-subject factors such as age, gender, previous mobile phone use and hemisphere exposed (right versus left hemisphere exposure). The results of the main study suggested that acute exposure to GSM900 mobile phone significantly reduced levels of psychological arousal, particularly in relation to selfratings of Energy. Results also indicated that only minutes of active exposure can lead to enhanced alpha EEG activity during active exposure relative to sham exposure. Interestingly, this effect was found to be transient, decreasing below sham levels after ten minutes of active exposure and up until ten minutes after exposure cessation. These exposure-induced changes in EEG alpha power were here interpreted as representing an overall reduction in integrative brain function, possibly caused by the physiological response to neural interference or altered synaptic transmission. Acute exposure did not alter human brain activity in the form of the early sensory or later cognitive ERP responses during an auditory or visual task, or EEG synchronisation during a higher cognitive task. The findings also suggested that resultant behaviour, as indexed by RT and accuracy, is unaffected by exposure. Conversely, exploration into specific groups within the sample resulted in some interesting interactions, which raised the possibility that active mobile phone exposure may affect individuals differently as a function of age, gender and which hemisphere is exposed. Specifically, the auditory processing of older individuals was particularly vulnerable to the detrimental effects of mobile phone exposure compared to their younger counterparts. Results of the visual task suggested that the performance of females may also be particularly vulnerable to the detrimental effects of active exposure, compared to males. Overall, the present study has confirmed that there are mobile phone-related bioeffects at the low levels that mobile phones are permitted to operate at. Although various effects have been observed, there is no indication from the present results that cumulative effects or any health consequences exist as this was not the focus of the research. It is argued that future investigation into mobile phone-related bioeffects should apply more sophisticated methodologies to the investigation of acute exposure on EEG alpha power and higher cognitive functioning, as well as larger sample sizes and fewer carefully planned comparisons in order to detect small effects. Further investigation into exposure-induced effects on different groups according to age, gender and which hemisphere is exposed should also be a priority.

Publication type

Thesis (PhD)

Research centre

Swinburne University of Technology. Faculty of Life and Social Sciences. Brain Sciences Institute

Publication year

2006

Keyword(s)

Cellular telephones;  Effect of radiation on the brain;  Electromagnetic fields;  Health;  Measurement

Coverage

Australasian Digital Theses collection

Copyright

Copyright © 2006 Denise L. Hamblin.

Thesis Supervisor

[Rodney J. Croft]

Thesis Note

[Submitted in fulfillment of the requirements for the degree of Doctor of Philosophy, Swinburne University of Technology, 2006.]

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