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.
| Identifer | oai:union.ndltd.org:ADTP/216607 |
| Date | January 2006 |
| Creators | Hamblin, Denise Lee, n/a |
| Publisher | Swinburne University of Technology. |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.swin.edu.au/), Copyright Denise Lee Hamblin |
Page generated in 0.0028 seconds