Summary
EMFs produced a broad array of impacts on the nervous system, ranging from changes in the electrical activity of specific areas of the brain, to systematic changes such as clinical zoonosis, enzyme increases, and alterations in specific and diffuse behavior. The most important characteristic of the reported effects was that the energy imparted to the organism under study was far too low to have energetically driven the observed changes via passive or classical processes such as ionization, heating, or gross alteration in the resting potential of membranes in excitable tissue. It was the metabolism of the organism, therefore, which furnished the energy, and the applied EMFs functioned primarily as eliciting, triggering, or controlling factors for the observed biological changes. There have been no systematic studies with one type of EMF, one organism, and one experimental paradigm. Consequently, it is difficult to generalize regarding the direction or trend that will likely be exhibited by specific nervous system parameters when they are measured under conditions which differ from those already studied. In this sense the present studies are unsatisfactory. But this problem can be remedied by future studies and it does not detract from the fundamental conclusion that nonthermal EMFs can cause electrical, biochemical, functional, and histopathological changes in the nervous system.
The manner and location at which the EMFs were detected and the means by which their existence was first communicated to the central nervous system-a dear prerequisite for any of the reported effects- cannot be determined from the present studies. The site of reception may be the central nervous system itself. Support for this can be found in studies in which brain electrical activity changes occurred instantaneously with the presentation of the field. By analogy with the modes of detection of other stimuli such as light, sound, or touch, it might also be suggested that the peripheral nervous system is the locus of EMF detection. This point can only be resolved by future studies - carefully designed to eliminate the recognized difficulties in recording electrical activity during EMF exposure (44) - in which nervous system electrical activity and the DC potentials are recorded during EMF exposure of the central and peripheral nervous systems separately.
Because the nature of the reception process of EMFs is unknown, it is not possible to determine whether it is mediated differently for EMFs with different frequency or amplitude characteristics. In contrast to this, the subsequent physiological events seem to proceed via common pathways regardless of the frequency of the applied EMF. Thus, altered brain electrical activity was found at 640 Hz (S), 3 GHz (6), and 9.3 GHz (68). Similarly, 50 Hz, (22), and 2.4 GHz (23) fields each produced comparable c hanges in enzyme levels in the brain. With regard to behavioral endpoints (reaction time, motor activity, conditioned responses), identical effects were found using EMFs that span the spectrum. Moreover, the EMFinduced effects were relatively independent of the type of applied field- whether electric or magnetic. For example, DC electric and magnetic fields each produced desychronization in the EEG (2), and low-frequency electric and magnetic fields each altered human reaction time (41, 42). Despite the observed nonspecificity of the biological effects with regard to the frequency or type of applied field, other characteristics of the applied EMFs did have a significant effect on the biological response. Pulse width and modulation frequency, for example, were important parameters in bloodbrain barrier penetration, interresponse times, and the self-stimulation response. Sometimes, pulsed EMFs produced biological effects at much lower average incident energy levels than was obtained with continuouswave EMFs, and in some cases only the pulsed EMF elicited an effect. Exposure duration also was an important factor in the elaboration of some effects. Thus, in general, the bioeffects were relatively independent of frequency and field type, but other signal characteristics were important in the development of the observed responses.
Dose:effect relationships were not manifested within or between studies. For example, in one instance a ten-factor increase in the strength of the applied field did not produce a corresponding increase in the brain enzyme level (24), and in a second case it produced a change opposite to that found at the lower field strength (23). The general absence of dose:effect relationships suggests that the EMFs had a trigger effect which was relatively independent of their magnitude. The field-induced effects, moreover, were time-dependent phenomena and for this reason, from a dose:effect viewpoint, it is not possible to compare the results of studies which used different exposure periods (36, 37).
The physical characteristics of the applied EMFs partially determined the biological effects. Another important - perhaps, in some cases, principal - factor in the production of such effects was the physiological state of the subject. About half the rabbits in Kholodov's study, for example, exhibited the sustained delta pattern: in the remaining animals it did not appear or it appeared only briefly. Bychkov found elevated and depressed EEG activity, or no effect at all, depending on the particular animal. The behavioral studies involving reaction time and motor activity clearly suggest that the subject's state of arousal was an important element in determining the direction, and perhaps the existence, of a field-induced effect. In all such cases, some factor, or combination of factors, peculiar to each animal was crucial in the elaboration of the effect. Sometimes - the zoonosis in the Friedman study, for example - such an operative factor was apparent. More frequently, however, they were simply uncontrolled variables (see chapter 8).
The overall pattern of the nervous system studies was one of detection and adaptation to the applied EMFs; an electrically diverse range of fields produced similar kinds of electrical, metabolic, and behavioral changes in the nervous system. At first glance it seems difficult to understand how different stimuli could produce similar responses, but this was exactly the situation which led Hans Selye, in 1936 (69), to propose his now established theory of biological stress (70): diverse stimuli - heat, cold, trauma, crowding, and many others - elicit a common physiological adaptive response in the organism. The response syndrome consists of measurable changes in the biochemistry, physiology, and histopathology of the neuroendocrine system, and in the organs and functions that are responsive to it. Any stimulus which elicits the syndrome is, by definition, a stressor.The idea that the electromagnetic field is a stressor is developed further in the succeeding chapters.