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Mobile Computing |
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ACM MC2R v3/#3, July, 1999
"Health Aspects of Wireless Communication"
CELLULAR TELEPHONES AND THEIR EFFECT ON THE HUMAN BRAIN
James C. Lin, lin@eecs.uic.edu, University of Illinois at Chicago, Chicago, IL, USA
Recently, there has been several print and broadcast media coverages of epidemiological studies from Sweden and the U.S. that focus on cell or mobile telephone use and brain tumors. They were referred to as Hardell and Muscat studies, respectively. Both studies are yet to be published. Also, neither study showed any overall increase in brain tumors, as compared to nonusers. However, there appeared to be a tendency toward greater likelihood (statistically not significant) to develop brain tumors on the side of the head where the phone is held. Researchers of the two studies have stated that their results were based on small numbers of cases, and must be interpreted with caution. Preliminary indications were that their cases and controls ranged from 200 to 500. The results would be more reliable if the numbers are circa 1500 in these studies. It is possible that the numbers would be greater by the time the studies are ready for publication.
These reports of unpublished results must be considered as preliminary observations at this moment. It is well to recall that the use of cellular telephones by the general population is a very recent event. Given the long latency of brain tumor development, a large increase in brain tumors over the short term would be a rare and unsettling phenomenon to behold. Moreover, epidemiological studies using small sample sizes are not always reliable. For example, a limited study of cancer incidences near the Sutton-Coldfield radio and TV towers in the U.K. indicated an increase in relative risk (1.83 from 1.00) of adult leukemia within 2 km. And there was a significant decline in risk in proportion with distance away from the towers for leukemia, and for bladder and skin cancers [1]. A follow-up study of 20 other broadcast sites in U.K. found an excess risk no more than 15% at any distance up to 10 km, and there was no observed excess within 2 km [2]. The authors of these Sutton-Coldfield studies suggested after the enlarged study that no more than a weak causal implication can be made.
A recent publication in the International Journal of Radiation Biology by Preece et al [3], suggested that exposure to RF radiation from simulated mobile telephone transmissions at 915 MHz may affect cognitive function in humans. In particular, the choice reaction time of 36 subjects, in randomized laboratory test sessions, showed a RF power-dependent increase in speed (a decrease in reaction time of 15 ms). There were no changes in short-term memory. At the time of its publication, the report touched off a flurry of news stories also. (Unfortunately, some media reports had erroneously alluded to RF exposure from cell phones affects memory, which has contributed to the controversy.)
Like other new findings, the implication of this laboratory study must await further scientific confirmation. Nevertheless, the conduction velocity of nerve impulses is known to rise, or fall in the case of conduction latency, with small increases in temperature. Changes in evoked responses of the central nervous system in vivo and spontaneous firing patterns of isolated neurons in vitro have been observed for temperature increases between 0.3 and 0.6 degree C. The rises in temperature were produced by exposure to 915 and 2450 MHz radiations, respectively [4.5]. Thus, the increase in responsiveness or decrease in choice reaction time of human volunteers is consistent with effects of mild localized heating of the underlying nervous tissue. The angular gyrus in the brain, on the same side as the cell phone antenna, acts as a relay station between the visual and speech foci. Therefore, the choice reaction time decrease could be associated with a thermal loading effect on the angular gyrus. It is possible that a nonthermal response, or direct interaction with the nervous system took place which is nevertheless RF power-dependent.
It should be noted that earlier investigations had ruled out a direct neural interaction of another phenomenon. The microwave auditory effect was thought to be a direct, nonthermal interaction of microwave radiation with the nervous system for hearing until it was proven otherwise. A train of RF pulses could be perceived as a tune corresponding to the pulse repetition rate [6,7]. It is generally accepted that the RF auditory effect does not arise from an interaction of RF pulses directly with the auditory nerves or neurons along the auditory pathway. Instead, RF pulses, upon absorption by soft tissues in the head, launches a thermoelastic wave of acoustic pressure that travels by bone conduction to the inner ear where it activates the cochlear receptors via the same process for normal hearing.
Some 270 scientific papers were presented at the Annual Bioelectromagnetics Society Meeting held on June 21-24 in Long Beach, California. At the meeting, Preece had elaborated on his finding that RF radiation from a mobile telephone affects cognitive function in human volunteers [8]. Among other presentations were laboratory, epidemiological, and mechanistic reports suggestive of central nervous system effects from exposure to low-level RF radiation emitted by a mobile phone. Others proposed that the association between RF radiation and such effects is weak or nonexistent. And, there were reports espousing a health connection is physically implausible. Overall, a majority of the reports presented at the meeting were works currently in progress.
Science takes time, wisdom, and money to blossom. During the normal course of scientific discovery, an inevitable quantity of time and effort must elapse in order for a consistent set of knowledge to emerge.
REFERENCES
[1] Dolk, H., G. Shaddick, P. Walls, C. Grundy, B. Thakrar, I. Kleinschmidt, and P. Elliott,1997, Cancer incidence near radio and television transmitters in Great Britain. 1. Sutton Coldfield transmitters, American Journal of Epidemiology,145:1-9.
[2] Dolk, H., P. Elliott, G. Shaddick, P. Walls, and B. Thakrar, 1997, Cancer incidence near radio and television transmitters in Great Britain .2. All high power transmitters, American Journal of Epidemiology,145:10-17.
[3] Preece A W., G. Iwi, A. Davies-Smith, K. Wesnes, S. Butler, E. Lim, and A. Varey, 1999, Effect of a 915-MHz simulated mobile phone signal on cognitive function in man. International Journal of Radiation Biology, 75:447-456.
[4] Guy, A.W., C.K. Chou, J.C. Lin and D. Christensen, 1975, Microwave induced acoustic effects in mammalian auditory systems and physical materials, Annals of New York Academy of Sciences, 247:194-218.
[5] Ginsburg, K, J.C. Lin, and W.D. O'Neill, 1992, "Microwave effects on input resistance and action potential firing of snail neurons, IEEE Trans on Biomedical Engineering, 39:1011-1021.
[6] Lin, J.C., 1980, The microwave auditory phenomenon, Proceedings of the IEEE, 68:67-73.
[7] Lin, J.C., 1999, "Health aspects of wireless communication," Mobile Computing and Communications Review, 3/1:14-20.
[8] Preece A.W. and A. Davies-Smith, 1999, "The effect of a 915 MHz simulated mobile phone transmission on cognitive function and cerebral blood flow in humans." presented at the Annual Bioelectromagnetics Society Meeting, June 21-24, Long Beach, California.
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Last modified 11/18/99