fields that they were exposed to chronically, and when the rats turned off the electric fields, they were given the opportunity to turn it on again. None of the rats performed differently in the presence of electric fields or in control conditions where electric fields were never present. As a control for the protocol, illumination from an incandescent light was used instead of electric fields. The incandescent light served as an aversive stimulus, and the rats turned the light off at a rate dependent on the intensity of the light. Results from these studies showed that 60-Hz electric fields at 100 kV/m are not a detectably aversive stimulus to rats. However, the mechanism through which the electric field acts is not known.
In one study, investigators attempted to determine whether the electric field could be exerting its effect through stimulation of the hair follicles or the skin rather than through a direct action on neuronal membranes (Weigel et al. 1987). Using the exposed surface of an anesthetized cat's paw, 60-Hz electric fields at up to 600 kV/m were applied while simultaneously recording from the sensory dorsal root fibers, which transduce afferent impulses that originate from various receptors in the exposed paw. The results clearly showed that electric fields can elicit activation of the cutaneous mechanoreceptors with persistent duration lasting up to 90 min in some cases without fatigue. The mechanism for that response could be through the vibration of the hair follicles or through displacement of the skin by the force of the field that stimulates the receptors. Those two external mechanisms are separate from the possibility of a direct interaction of the induced currents produced in the skin with the neuronal membranes that stimulate the receptor to fire. By shaving the hair off the paw and applying mineral oil to the paw, a significant reduction in firing rate to stimulation was recorded, suggesting that the major part, but not necessarily all, of the mechanism for electric-field detection is through vibrations of the skin and hair.
Although signal detection methods have provided evidence of the ability of mammals to detect electric fields, such evidence is not available for magnetic fields except at very high field strengths (i.e., magnetic excitation of endogenous phosphenes). A comprehensive series of studies examined the effects of chronic exposure of nonhuman primates to 60-Hz electric and magnetic fields on general health and behavioral performance, chemistry, and neurophysiology. In the first study, Wolpaw et al. (1989) exposed pigtail macaque primates to electric and magnetic fields at 3 kV/m and 10 µT, 10 kV/m and 30 µT, and 30 kV/m and 90 µT, respectively, for three 21-day periods; 21-day sham exposures preceded and followed the experimental period. General health examinations, including weight, blood chemistry, blood-cell counts, performance on a simple motor task, and postmortem examinations, were conducted on the animals. No detectable effects of electric and magnetic fields were discernible between sham exposures and experimental periods.