PERCEPTION AND BEHAVIORAL EFFECTS OF ELECTROMAGNETIC FIELDS
Some animals respond to extremely low levels of electromagnetic fields (EMF), usually at frequencies ranging from DC to extremely-low-frequency (ELF) and usually with specialized receptors.1 Although the responses have been described and can be demonstrated at will, the mechanisms are not understood. Perceptual and behavioral responses to very low levels of EMFs at low frequency and above have not been reported in humans, and there are no mechanisms at DC or ELF that might imply as yet unreported responses, although they cannot be excluded. There is a considerable literature on perception and behavioral responses to stimulation at magnitudes consistent with direct electrical stimulation of nervous tissues by induced currents in the tissue, but they are limited to the frequency ranges that stimulate excitable membranes.
In the radiofrequency (RF) range of concern for assessment of GWEN sites, there have been many reports of sensory perception. The responses may be organized in the following categories:
Stimulation of nervous structures by electric and magnetic fields and associated currents in the body. Above a threshold that is frequency-dependent, these currents are perceived as a painful stimulus that increases with current intensity.
Electroencephalographic (EEG) activity in cats and rabbits has been reported to be altered by exposure to amplitude-modulated RF. Exposure to 147-MHz fields, amplitude-modulated between 1 and 25 Hz, altered the ability of cats to produce selected EEG rhythms. Changes in EEG frequency spectrum were also observed in rabbits chronically exposed to 1-10 MHz fields that were amplitude-modulated at 14-16 Hz.2 Other studies have shown small changes in EEG patterns, particularly desynchronization, in rats and rabbits after exposure to 12.95-GHz field at 1 W/kg.3,4 Some later studies failed to find an effect. The lowest levels used, in the above studies are 10,000 times that which would be encountered near GWEN installations.
Shocks and burns. When the human body is in an EMF of suitable frequency and intensity and it makes contact with a conducting body in the same field, an electrical current is produced that can cause perceptible electrical shock, muscular contractions, burns, and possible death.
Heating. If enough RF power is absorbed in human tissue, especially skin, it can raise the tissue temperature and cause a sensation of warming that will be due to thermal stimulation of temperature receptors. Thermal perception of absorbed RF energy is frequency-dependent: the threshold energy decreases as the frequency increases.5 There is a delay in the perception of warmth after the start of irradiation; the delay may vary from 5 sec or more at GHz frequencies to as little as 1 sec for
infrared radiation.6 Justesen et al.7 compared thermal perception in human volunteers who were irradiated on the forearm in a 100-cm2 area with far-infrared radiation or 2.45-GHz microwave radiation. The thresholds of perception for a 10-sec exposure were 1.7 mW/cm 2 for far infrared radiation and 26.7 mW/cm2 for microwave radiation.
Auditory perception. A special effect has been reported in which microwave RF emitted in the form of very short pulses (1-20 µsec) is perceived by humans and animals as clicks or other sounds. This perception could well result when thermal absorption leads to thermoelastic expansion of tissues and fluids in the head and is sensed by auditory receptors. If the energy flux in the pulse exceeds about 40 µJ/cm2, delivered in a few microseconds, auditory perceptions occur.8
The auditory perception of pulsed microwave fields was first reported in 1947 and has been studied extensively. Frey9 reported on controlled experimental exposures at frequencies of 0.2-8.9 GHz and pulse widths of 1-1,000 µsec. He found that, depending on the characteristics of the field, sensations were perceived as buzzing, ticking, hissing, or knocking sounds. Sound was perceived at all frequencies up to 8.9 GHz. Guy et al.10 demonstrated that the threshold for auditory perception was four times higher at 3.75 kHz in subjects with neurosensory deficits compared with normal subjects, thus indicating that the effect was in the acoustic elements involved in hearing.
Behavioral changes. Epidemiologic studies of groups of people occupationally or environmentally exposed to electromagnetic fields in the RF and ELF range have yielded perceptual and behavioral responses, including fatigue, difficulty in concentrating, and increased frequency of headaches. A number of researchers have used disruption of behavior patterns, such as work stoppage, to study the effect of RF fields on animals, including rodents11,12,13 and monkeys.14 Several carrier frequencies, field zones, and modulation characteristics were used. A relatively narrow range of threshold of specific absorption rates (SARs), about 4-9 W/kg, was found. Lebovitz15 examined the effect of repeated exposures to a pulsed 1,300-MHz field on behavioral performance in rats. He exposed animals to SARs of 1.6, 3.6, or 6.7 W/kg for 3 h/day, 5 d/wk for 6-9 wk and found that rates of lever-pressing for food were slightly reduced at the highest SAR. However, the ability of the rats to discriminate improved as a positive function of SAR when lever-pressing was not reinforced by the presence of food. DeLorge16 used a different experimental paradigm and showed a disruption in performance of rats at an SAR of 2.5 W/kg when they were exposed to a pulsed 1,300-MHz field. Behavioral studies performed by Hjeresen et al.17 showed that rats placed in a shuttlebox tended to remain in the side shielded from pulsed RF fields. Because the rats also tended to avoid pulsed sound waves, the investigators suggested that the rats' avoidance of the RF fields might be related to the hearing of the pulsed fields. The response to a pulsed field is stronger than that to a continuous field. For example, Carroll et al.18 found that rats exposed to an intense field that was not pulse-modulated did not readily learn to escape from it. It appears that hearing the pulses is a more effective cue for escaping than is the warming that results from a continuous field.
Studies in Eastern Europe have investigated populations exposed to EMFs ranging from 50 Hz to microwave frequencies.19 Complaints included irritability, lethargy, insomnia, impotence, headaches, loss of memory, and inability to concentrate. The syndrome was identified as neurasthenia or “microwave sickness.” Energy magnitudes associated with the syndrome have been reported for a few microwatts to a few thousand microwatts per square centimeter. An epidemiologic study of the personnel in the American embassy in Moscow found an excess of the same neurasthenic symptoms, but the symptoms were not correlated with measured individual exposures.20
Eastern European investigators have also reported on rats and rabbits exposed for one to several hours a day over periods of weeks or months. Power densities ranging from 0.6 to 30,000 µW/cm2 were reported to alter conditional reflexes21 and decrease latency of audiogenic seizures.22 Attempts to confirm the findings were made by several investigators; some effects of exposure to RF fields were found, but most were at higher field intensities, and in general the results did not support the findings from Eastern Europe.
Studies with ELF fields have suggested that behavior can be influenced by exposure to either magnetic or electric fields. Persinger23 reported that prenatal exposure of rats to 0.5-Hz, 0.05- to 3-mT fields, resulted in changes in juvenile or adult rats' emotionality and ability to perform a conditioned-suppression test. Frey24 found that prenatal exposure of rats to a 60-Hz field at 3.5 kV/m caused changes in open-field activity.
McGivern et al.25 studied male rats that had been exposed prenatally on days 15-21 of gestation. Exposures were for 15 min twice a day, to a 15-Hz, 800-µT pulsed magnetic field. Exposed animals showed a significant reduction in scent-marking, compared with sham-exposed or caged controls. Exposed males had larger seminal vesicles, prostates, and epididymides than did control males.
Transient neurobehavioral changes in rats exposed prenatally and postnatally to a 60-Hz electric field (65-kV/m effective field) were reported by Sikov et al.26 Exposed animals showed significantly more motility than did controls. Development of righting reflex and negative geotropism was also delayed in exposed rats; the percentage of pups that failed to show these behaviors was increased on day 14 of postnatal life, but not on day 21.
Lovely et al.27 exposed gravid Sprague-Dawley rats to a 60-kV/m, 60-Hz electric field and then tested the offspring at the age of 90 days in three tasks: shuttlebox avoidance, a residential maze, and a preference-avoidance test. No differences were noted between exposed and sham-exposed animals.
Changes in learning have been reported in rats exposed to a combination of 60-Hz electric fields (30 kV/m and 0.1 mT) and magnetic fields (10 kV/m and 0.033 mT) throughout gestation and during the first 8 days of postnatal life.28 Both acquisition and extinction of a schedule-controlled response were affected in the exposed animals. In contrast, other studies failed to find an effect of exposure to ELF fields on behavior.29,30
Exposure to 60-Hz electric fields (30 or 60 kV/m) has been reported to affect the social behavior of baboons.31,32 The investigators used a number of measures of social behavior, but found that passive affinity, tension, and stereotypy performance were significantly increased in exposed groups. The authors suggested that the changes might indicate a stress response to the fields.
Although there is evidence that exposure of experimental animals to electric or magnetic fields can influence neurobehavioral function, there is a paucity of direct observations at the 175-kHz frequency and at the ultra-high frequencies of 200-400 MHz used in the GWEN system. Moreover, magnitudes of the exposure usually required to produce an effect are substantially higher than those likely to be encountered as a result of operation of the GWEN system. It therefore seems unlikely that electromagnetic fields from GWEN will affect neurosensory or neurobehavioral function in persons living around GWEN sites.
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2. Takeshima, S., B. Onaral, and H. P. Schwan. 1979. Effects of modulated RF energy on the EEG of mammalian brains: effects of acute and chronic irradiations. Radiat. Environ. Biophys. 16 : 15-27.
3. Baranski, S., and Z. Edelwejn. 1975. Experimental morphologic and electroencephalographic studies of microwave effects on the nervous system. Ann. N. Y. Acad. Sci. 277 : 109-116.
4. Servantie, B., A. M. Servantie, and J. Etienne. 1975. Synchronization of cortical neurons by a pulsed microwave field as evidenced by spectral analysis of electrocorticograms from the white rat. Ann. N. Y. Acad. Sci. 247 : 82-86.
5. Hendler, F., J. D. Hardy, and D. Murgatroyd. 1963. Skin temperature and temperature sensation produced by infrared and microwave irradiation. Biology and Medicine Vol. 3, Temperature: its measurement and control in Science and Industry, C. M. Hertzfeld, ed. New York: Reinhold Publishing Corp.
6. Eijkman, E., and A. J. H. Vendrik. 1961. Dynamic behavior of the warmth sense organ. J. Exp. Psychol. 62 : 403-408.
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8. Lin, J. C. 1990. Auditory perception of pulsed microwave radiation. Pp. 277-318 in Biological Effects and Medical Applications of Electromagnetic Energy , O. P. Ghandi, ed. Englewood Cliffs, New Jersey : Prentice Hall.
9. Frey, A. H. 1961. Auditory system response to modulated electromagnetic energy. J. Appl. Phys. 17 : 689-692.
10. Guy, A. W., C.-K. Chou, J. C. Lin, and D. Christensen. 1975. Microwave induced acoustic effects in mammalian auditory systems and physical materials. Ann. N.Y. Acad. Sci. 247 : 194-218.
11. Justesen, D. R., and N. W. King. 1970. Behavioral effects of low level microwave irradiation in the closed space situation. Pp. 154-179 in Biological Effects and Health Implications of Microwave Radiation , S. F. Cleary, ed. HEW Publication BRH/DBE 70-2.
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14. DeLorge, J. O. 1979. Operant behavior and rectal temperature of squirrel monkeys during 2.45 GHz microwave irradiation. Radio Sci. 12 : 217-225.
15. Lebovitz, R. M. 1981. Prolonged microwave irradiation of rats: effects on concurrent operant behavior. Bioelectromagnetics 2 : 169-185.
16. DeLorge, J. O. 1983. The thermal basis for disruption of operant behavior by microwaves in three species. Pp. 379-399 in Microwaves and Theroregulation, E. R. Adair, ed. Academic Press : New York.
17. Hjeresen, D. L., S. R. Doctor, and R. L. Sheldon. 1979. Pp. 194-214 in Proceedings of the Symposium on Electromagnetic Fields in Biological Systems, S. S. Stuchly, ed. International Microwave Power Institute, Edmonton, Canada.
18. Carroll, D. R., D. M. Levinson, D. R. Justesen, and R. L. Clarke. 1980. Failure of rats to escape from a potentially lethal microwave field . Bioelectromagnetics 1 : 101-115.
19. Sadchikova, M. W. 1974. Clinical manifestations of reactions to microwave irradiation in various occupational groups. Pp. 261-268 in Biological Effects and Health Hazards of Microwave Radiation, P. Czerski, K. Ostraowski, C. Silverman, M. L. Shore, M. J. Suess, and B. Waldeskog, eds. Warsaw : Polish Medical Publishers.
20. Lilienfeld, A. M., J. Tonascia, S. Tonascia, C. H. Libauer, G. M. Cauthen, J. A. Markowitz, and S. Weida. 1978. Foreign Service Health Status Study-Evaluation of the Health Status of Foreign Service and Other Employees from Selected Eastern European Posts. Final Report Contract 6025-619073. Washington, D.C. : Department of State.
21. Lobanova, E. A. 1974. The use of conditional reflexes to study microwave effects on the central nervous system. Pp. 109-118 in Biologic Effects and Health Hazards of Microwave Radiation, P. Czerski et al., eds. Warsaw : Polish Medical Publishers.
22. Stverak, I., K. Marha, and G. Pafkova. 1974. Some effects of various pulsed fields on animals with audiogenic epilepsy. 1974. Pp. 141-144 in Biologic Effects and Health Hazards of Microwave Radiation, P. Czerski, K. Ostrowski, C. Silverman, J. L. Shore, M. J. Suess, and B. Waldeskog, eds. Warsaw : Polish Medical Publishers.
23. Persinger, M. A. 1969. Open field behavior in rats exposed prenatally to a low intensity-low frequency, rotating magnetic field. Developmental Psychobiol. 2 : 168-171.
24. Frey, A. H. 1982. Neural and behavioral consequences of prenatal exposure to 3.5 kV/m 60 Hz fields. Abstr. 4th Annual Meeting Bioelectromagnetics Society, Los Angeles, California.
25. McGivern, R. F., R. Z. Sokol, and W. R. Adey. 1990. Prenatal exposure to low-frequency electromagnetic field demasculinizes adult scent marking behavior and increases accessory sex organ weights in rats. Teratology 41 : 1-8.
26. Sikov, M. R., L. D. Montgomery, L. G. Smith, and R. D. Phillips. 1984. Studies on prenatal and postnatal development in rats exposed to 60-Hz electric fields. Bioelectromagnetics 5 : 101-112.
27. Lovely, R. H., J. A. Creim, and R. D. Phillips. 1984a. Adult behavioral effects of prenatal and early postnatal exposure to 60-Hz electric fields in rats. In Interaction of Electromagnetic Fields with Biological System. Twenty-first General Assembly of the International Union of Radio Science (URSI), August 27-30, 1984, Florence, Italy (abstract).
28. Salzinger, K., S. Freimark, M. McCullough, D. Phillips, and L. Birenbaum. 1990. Altered operant behavior of adult rats after perinatal exposure to a 60-Hz electromagnetic field. Bioelectromagnetics 11 : 105-116.
29. Lovely, R. H., J. A. Creim, and R. D. Phillips. 1984. Effects of prenatal exposure to 60-Hz electric fields on open field and maze performance of F-2 generation Hanford Miniature swine. Pg. 10 in Sixth Annual Scientific Session of the Bioelectromagnetics Society , July 15-19, Atlanta, Georgia (abstract).
30. Durfee, W. K., P. R. Plante, P. Martin, S. Muthukrishman, and C. Polk. 1976. Exposure of domestic fowl to ELF electric and magnetic fields. In Biological Effects of Electromagnetic Waves, C. C. Johnson, and M. L. Shore (eds). Selected papers of the USNC/URSI Annual Meeting, Boulder, CO, October 20-23, 1975. Vol. 1. Washington, D.C.: U.S. Government Printing Office.
31. Easley, S. P., A. M. Coelho, Jr., and W. R. Rogers. 1991. Effects of exposure to a 60 kV/m, 60-Hz electric field on the social behavior of baboons. Bioelectromagnetics 12 : 361-375.
32. Coelho, A. M., Jr., G. P. Easley, and W. R. Rogers. 1991. Effects of exposure to a 60 kV/m, 60-Hz electric field on the social behavior of baboons. Bioelectromagnetics 12 : 361-375.