Acute exposure to power-frequency magnetic fields has no effect on the acquisition of a spatial learning task by adult male mice

A series of four experiments was performed to determine whether acute exposure to a range of 50 Hz magnetic fields had any effect on a learning task in adult male CD1 mice. A radial-arm maze placed within the bore of an electromagnet was used to assess spatial discrimination learning for food reward. Subjects were reduced to 85% of their free-feeding weight and were placed in the maze for up to 15 minutes each day for 10 days. Performance of the task was measured by using maximum likelihood techniques to calculate the probability that an animal would not reenter any given arm of the maze. Experimental subjects were exposed to a vertical, 50 Hz sinusoidal magnetic field at 5 μT, 50 μT, 0.5 mT, or 5.0 mT (rms). Control subjects were exposed only to a background time-varying field of less than 50 nT and the ambient static field of about 40 μT. The variation in the applied magnetic field was less than 5% except at the ends of the arms, where it approached 10%. It was found that all eight groups of subjects (n = 10 in all cases) showed similar increases in performance with testing, and the acquisition curve for each group of experimental subjects was not significantly different from that of their control group (P > 0.05 in all cases). It was concluded that exposure had no effect on learning at any flux density. This result is contrary to the findings of a number of preliminary studies, although other studies have reported that magnetic fields do not affect spatial learning in adult male rodents. It is possible that differences between experimental conditions might explain some of this apparent discrepancy. © 1996 Wiley-Liss, Inc.     

50 Hz magnetic field effects on the performance of a spatial learning task by mice

Intense magnetic fields have been shown to affect memory-related behaviours of rodents. A series of experiments was performed to investigate further the effects of a 50 Hz magnetic field on the foraging behaviour of adult, male C57BL/6J mice performing a spatial learning task in an eight-arm radial maze. Exposure to vertical, sinusoidal magnetic fields between 7.5 μT and 7.5 mT for 45 min immediately before daily testing sessions caused transient decreases in performance that depended on the applied flux density. Exposure above a threshold of between 7.5 and 75 μT significantly increased the number of errors the animals made and reduced the rate of acquisition of the task without any effect on overall accuracy. However, the imposition of a 45-minute delay between exposure at 0.75 mT and behavioural testing resulted in the elimination of any deficit. Similarly, exposure to fields between 7.5 μT and 0.75 mT for 45 min each day for 4 days after training had no amnesic effects on the retention and subsequent performance of the task. Overall, these results provide additional evidence that 50 Hz magnetic fields may cause subtle changes in the processing of spatial information in mice. Although these effects appear dependent on field strength, even at high flux densities the field-induced deficits tend to be transient and reversible. Bioelectromagnetics 19:486–493, 1998. © 1998 Wiley-Liss, Inc.     

Single, brief exposure to a 50 Hz magnetic field does not affect the performance of an object recognition task in adult mice

A number of studies have shown that power frequency magnetic fields may affect spatial memory functions in rodents. An experiment was performed using a spontaneous object recognition task to investigate if nonspatial working memory was similarly affected. Memory changes in adult, male C57BL/6J mice were assessed by measuring the relative time within which the animals explored familiar or novel stimulus objects. Between initial testing and retesting, the animals were exposed for 45 min to a 50 Hz magnetic field at either 7.5 microT, 75 microT or 0.75 mT. Other animals were sham-exposed with ambient fields of less than 50 nT. No significant field-dependent effects on the performance of the task were observed at any flux density (for all measures, P > 0.05). These data provide no evidence to suggest that nonspatial working memory was affected in mice by acute exposure to an intense 50 Hz magnetic field.     

磁场对小鼠两种迷宫学习记忆的影响

据发现,磁场对生物体有一定作用,但是磁场对于人类或实验动物的学习记忆是否有影响,目前的报道结果很不一致。本实验采用实验小白鼠,给予不同强度（65高斯／50Hz,35高斯/25Hz）的低频磁场照射（每天1小时,持续25天）。磁场照射后,采用旷场行为测试、Y-迷宫和Morris水迷宫,检测小鼠的活动性、空间辨别、空间学习记忆和非空间学习记忆能力。结果表明：65高斯／50Hz磁场显著增高小鼠的活动性,并损伤小鼠Y-迷宫的空间辨别能力,但对Morris水迷宫的空间、非空间学习记忆无明显影响。35高斯／25Hz磁场处理动物行为在三个指标上均接近对照组。提示：长期的磁场照射可能会给动物,甚至人类造成一些影响。     

A magnetic field effect on learning in male golden hamsters

The aim of this experiment was to investigate the influence of repeated exposure to 10, 20, 30 or 40 Hz magnetic fields at 0.1 T on the learning of male golden hamsters in a Skinner box, in which the animals learned to press a lever to receive a food reward. The latency of the first response was not affected by exposure to the magnetic fields used in this experiment. No significant field-dependent effects on the performance of the task were observed in males exposed to 10 and 20 Hz magnetic fields at 0.1 T. However, exposure significantly improved the learning of the task in animals exposed to 30 and 40 Hz magnetic fields at 0.1 T.     

Brief exposure to a 50 Hz, 100 microT magnetic field: effects on reaction time, accuracy, and recognition memory

The present study investigated both the direct and delayed effects of a 50 Hz, 100 microT magnetic field on human performance. Eighty subjects completed a visual duration discrimination task, half being exposed to the field and the other half sham exposed. The delayed effects of this field were also examined in a recognition memory task that followed immediately upon completion of the discrimination task, Unlike our earlier studies, we were unable to find any effects of the field on reaction time and accuracy in the visual discrimination task. However, the field had a delayed effect on memory, producing a decrement in recognition accuracy. We conclude that after many years of experimentation, finding a set of magnetic field parameters and human performance measures that reliably yield magnetic field effects is proving elusive. Yet the large number of significant findings suggests that further research is warranted.     

Acute exposure to a 60 Hz magnetic field affects rats' water-maze performance

Rats were trained in six sessions to locate a submerged platform in a circular water-maze. They were exposed to a 1 mT, 60 Hz magnetic field for one hour in a Helmholtz coil system immediately before each training session. In addition, one hour after the last training session, they were tested in a probe trial during which the platform was removed and the time spent in the quadrant of the maze in which the platform was located during the training sessions was scored. Control animals were sham-exposed using the exposure system operating with the coils activated in an anti-parallel direction to cancel the fields. A group of “non-exposed” control animals was also included in the study. There was no significant difference between the magnetic field-exposed and control animals in learning to locate the platform. However, swim speed of the magnetic field-exposed rats was significantly slower than that of the controls. During the probe trial, magnetic field-exposed animals spent significantly less time in the quadrant that contained the platform, and their swim patterns were different from those of the controls. These results indicate that magnetic field exposure causes a deficit in spatial “reference” memory in the rat. Rats subjected to magnetic field exposure probably used a different behavioral strategy in learning the maze. Bioelectromagnetics 19: 117–122, 1998. © 1998 Wiley-Liss, Inc.     

Effects of exposure to a 50 Hz sinusoidal magnetic field during the early adolescent period on spatial memory in mice

Adolescence is a critical developmental stage during which substantial remodeling occurs in brain areas involved in emotional and learning processes. Although a robust literature on the biological effects of extremely low frequency magnetic fields (ELF‐MFs) has been documented, data on the effects of ELF‐MF exposure during this period on cognitive functions remain scarce. In this study, early adolescent male mice were exposed from postnatal day (P) 23–35 to a 50 Hz MF at 2 mT for 60 min/day. On P36–45, the potential effects of the MF exposure on spatial memory performance were examined using the Y‐maze and Morris water maze tasks. The results showed that the MF exposure did not affect Y‐maze performance but improved spatial learning acquisition and memory retention in the water maze task under the present experimental conditions. Bioelectromagnetics 34:275–284, 2013. © 2012 Wiley Periodicals, Inc.     

Acute exposure to 50 Hz magnetic field does not affect hematologic or immunologic functions in healthy young men: A circadian study

Some epidemiological studies report a relationship between magnetic field exposure and such human diseases as leukemia and immune system disturbances. The few published studies on animals do not demonstrate field exposure-related alterations in hematologic and immune systems. The data presented here are part of a broader study designed to investigate the possible effects of acute exposure to a 50 Hz linearly polarized magnetic field (10 μT) on hematologic and immunologic functions. Thirty-two young men (20–30 years old) were divided into two groups (control group, i.e., sham-exposed, 16 subjects; exposed group, 16 subjects). All subjects participated in two 24 h experiments to evaluate the effects of both continuous and intermittent (1 h “off” and 1 h with the field switched “on” and “off” every 15 s) exposure to linearly polarized magnetic fields. The subjects were exposed to the magnetic field (generated by three Helmholtz coils per bed) from 23:00 to 08:00 while lying down. Blood samples were collected during each session at 3 h intervals from 11:00 to 20:00 and hourly from 22:00 to 08:00. No significant differences were observed between sham-exposed (control) and exposed men for hemoglobin concentration, hematocrit, red blood cells, platelets, total leukocytes, monocytes, lymphocytes, eosinophils, or neutrophils. Immunologic variables [CD3, CD4, CD8, natural killer (NK) cells and B cells] were unaltered. To our knowledge, this study is the first to document the effects of a 50 Hz magnetic field on the circadian rhythm of human hematologic and immune functions, and it suggests that acute exposure to either a continuous or an intermittent 50 Hz linearly polarized magnetic field of 10 μT, at least under the conditions of our experiment, does not affect either these functions or their circadian rhythms in healthy young men. © 1996 Wiley-Liss, Inc.     

Acute effects of 50 Hz, 100 μT magnetic field exposure on visual duration discrimination at two different times of the day

A two-alternative, forced-choice visual duration discrimination task was used to examine the effect of an intermittent, 50 Hz, 100 μT magnetic field on accuracy at two different times of the day. A total of 59 female and 40 male subjects with an age range of 18 to 46 years were studied under both field-exposed and sham-exposed conditions. The subject's task was to decide which of two sequentially presented light flashes had the longer duration, percentage correct being the measure of performance. The data were gathered under double-blind conditions with sham and real exposure counterbalanced. Exposure to the magnetic field produced a small improvement in accuracy but only at the most difficult level of the task, with female subjects showing a larger improvement than males. The time of day at which the study was run had no effect on performance. Despite the relatively large number of subjects used and a relaxed alpha level (P = .3), the statistical power of the test to detect the observed effect was still only 0.71. Bioelectromagnetics 19:310–317, 1998. © 1998 Wiley-Liss, Inc.     

Long-term exposure of male and female mice to 50 Hz magnetic field: effects on fertility

The effect of an extremely low frequency (ELF) magnetic field on the fertility of adult male and female Swiss mice was investigated. Adult male and female mice were exposed to a 50 Hz sinusoidal magnetic field at approximately 25 microT (rms) for 90 days before they were mated with unexposed counterparts. There were no exposure related effects on the fertility of male or female mice. The number of implantation sites, viable fetuses, and the total number of resorptions were not significantly affected in females impregnated by males exposed to the 50 Hz magnetic field as compared with the control group. The number of implantation sites, viable fetuses and the total number of resorptions in exposed females were also not statistically different from the control group. There were no significant effects on the weights of the testes, seminal vesicles, preputial gland or body weights of males exposed to 50 Hz magnetic field. Furthermore, body and uterine weights were not affected in females exposed to 50 Hz field; however, ovarian weight was significantly increased in females exposed to the same field. These results suggest that exposure of male and female mice to low frequency magnetic field had no adverse effects on fertility and reproduction in mice.     

50 Hz magnetic field exposure influence on human performance and psychophysiological parameters: two double-blind experimental studies

Two double-blind studies were performed to examine magnetic field (MF) exposure effects and to determine the impact of temporal variation (continuous vs. intermittent exposure) of 100 mu T(rms) 50 Hz MF diurnal exposure on psychological and psychophysiological parameters in healthy humans. Three cephalic exposure sessions of 30-min, i.e., sham, continuous, and intermittent (15 s ON/OFF cycles) MF conditions, were involved. Each subject participated in all sessions, which were spaced at 1-wk intervals. In each session, mood ratings and performance measures were obtained before, during, or after exposure and several electrophysiological data (event-related brain potentials [ERP]) were recorded after each exposure session. These criteria were chosen to evaluate sensory functions as well as automatic and voluntary attentional processes. In experiment 1, 21 healthy male volunteers (20 to 27 years of age) were studied. Ten subjects were exposed at 13:30 h, and 11 subjects were exposed at 16:30 h. Statistically significant changes in the amplitude of ERP were observed after MF exposure in the dichotic listening task, indexing selective attention processes. Eighteen of the 21 original male volunteers took part in experiment 2, undertaken to better understand the results related to information processing involved in selective attention and control for ultradian rhythmicity. Exposure time for all the subjects was at 13:30 h. The analysis of the data again revealed significant amplitude changes of the ERP recorded in the dichotic listening task. Moreover, they demonstrated ERP latency and reaction time slowing in the oddball paradigm, a visual discrimination task after real MF exposure. These results also indicate that a low level 50 Hz MF may have a slight influence on event-related potentials and reaction time under specific circumstances of sustained attention.     

Spatial learning deficit in the rat after exposure to a 60 Hz magnetic field

Rats were trained in ten daily sessions to perform in a 12-arm radial maze, which is a behavioral test for spatial memory functions. Exposure to a 60 Hz magnetic field (45 min, 0.75 mT) immediately before each training session retarded learning significantly. Pretreatment with the cholinergic agonist physostigmine before magnetic field exposure reversed the field's effect on spatial learning. Data from this experiment indicate that magnetic field-induced spatial learning deficit is caused by the effect of the field on cholinergic systems. © 1996 Wiley-Liss, Inc.     

Increased dexamethasone-induced apoptosis of thymocytes from mice exposed to long-term extremely low frequency magnetic fields

To address the effect of extremely low frequency electromagnetic fields on programmed cell death we assessed both the spontaneous and dexamethasone (Dex)-induced apoptosis of thymocytes and spleen cells from mice submitted to a long-term continuous exposure of a 0.4–1.0 μT 60 Hz magnetic field or an 8–20 μT direct current (DC) magnetic field. Dex-induced apoptosis but not spontaneous apoptosis was substantially increased in thymocytes from 0.4 to 1.0 μT 60 Hz field-exposed animals. Spontaneous apoptosis and Dex-induced apoptosis of spleen cells were not affected by the 0.4–1.0 μT 60 Hz field exposure. In addition, spontaneous apoptosis and Dex-induced apoptosis of thymocytes and spleen cells from mice exposed to an 8–20 μT DC field were similar to the controls. These findings represent the first demonstration that thymocytes from mice exposed to a long-term 0.4–1.0 μT 60 Hz field may show abnormal response to Dex apoptotic stimuli. Bioelectromagnetics 19:131–135, 1998. © 1998 Wiley-Liss, Inc.     

Prenatal exposure to a 50 Hz magnetic field has no effect on spatial learning in adult mice

Male CD1 mice were exposed in utero to a 50 Hz sinusoidal magnetic field at 5 mT (rms) for the period of gestation and were raised subsequently without applied fields. At 82-84 days of age, they began a radial-arm-maze experiment that was designed to test for deficits in spatial learning in memory. Mice exposed in utero and sham-exposed mice exhibited no statistically significant differences in performances. © 1996 Wiley-Liss, Inc.     

Do ELF magnetic fields affect human reaction time?

Two double-blind studies were run in an attempt to confirm the finding that a 0.2 Hz magnetic field affects simple reaction time (RT) in humans, whereas a 0.1 Hz field does not. In the first experiment, 12 volunteer subjects were exposed to a continuous 0.2 Hz, 0.1 Hz, or sham field in a fully counter-balanced, within-subjects design. Subjects were run singly for one condition each day over 3 consecutive days with a field strength of 1.1 mT and a daily exposure duration of 5 min. Neither magnetic field had any effect on RT at any time during the exposure. One condition of a second study, using a new group of 24 volunteer subjects, also failed to find any field effects at 0.2 Hz. Additionally, the second study failed to show any effects when the frequency, flux density, and field orientation were set according to parametric resonance theory. It is suggested that, although ELF magnetic field effects on human behaviour may be elusive, future research can improve detection rates by paying greater attention to reducing error variance and increasing statistical power. © 1995 Wiley-Liss, Inc.     

Effect of sinusoidal 50 Hz magnetic field on the testosterone production of mouse primary Leydig cell culture

This study evaluated the effect of sinusoidal 50 Hz magnetic field on the basal and human chorionic gonadotropin (hCG)-stimulated testosterone (T) production of 48-h mouse Leydig cell culture. The luteinizing hormone (LH) analog hCG was used to check the T response of the controls and to evaluate the possible effect of the applied magnetic field on the steroidogenic capacity of the exposed cells. Leydig cells were obtained from the testes of 35- to 45-g CFLP mice and isolated by mechanical dissociation without enzyme treatment. The cell cultures were exposed to sinusoidal 50 Hz 100 μT (root mean square) AC magnetic field during the entire time of a 48-h incubation. Testosterone content of the culture media was measured by radioimmunoassay. In cultures exposed to the magnetic field, a marked increase of basal T production was found (P < .05), compared with the unexposed controls, whereas no significant difference was seen between the exposed or unexposed cultures in the presence of maximally stimulating concentration of hCG. These findings demonstrate that sinusoidal 50 Hz 100 μT magnetic fields are able to stimulate the basal T production of primary mouse Leydig cell culture, leaving the steroidogenic responsiveness to hCG unaltered. Bioelectromagnetics 19:429–431, 1998. © 1998 Wiley-Liss, Inc.     

Thresholds for 60 Hz magnetic field stimulation of peripheral nerves in human subjects

The goal of the research reported here is to narrow the range of uncertainty about peripheral nerve stimulation (PNS) thresholds associated with whole body magnetic field exposures at 50/60 Hz. This involved combining PNS thresholds measured in human subjects exposed to pulsed magnetic gradient fields with calculations of electric fields induced in detailed anatomical models of the body by that same exposure system. PNS thresholds at power frequencies (50/60 Hz) can be predicted from these data due to the wide range of pulse durations (70 mus to 1 ms), the length of the pulse trains (several tens of ms), and the exposure of a large part of the body to the magnetic field. These data together with the calculations of the rheobase electric field exceeded in 1% (E(1%)) of two anatomical body models, lead to a median PNS detection threshold of 47.9 +/- 4.4 mT for a uniform 60 Hz magnetic field exposure coronal to the body. The threshold for the most sensitive 1% of the population is about 27.8 mT. These values are lower than PNS thresholds produced by magnetic fields with sagittal and vertical orientations or nonuniform exposures.     

Hypothesis: The risk of childhood leukemia is related to combinations of power-frequency and static magnetic fields

We present a hypothesis that the risk of childhood leukemia is related to exposure to specific combinations of static and extremely-low-frequency (ELF) magnetic fields. Laboratory data from calcium efflux and diatom mobility experiments were used with the gyromagnetic equation to predict combinations of 60 Hz and static magnetic fields hypothesized to enhance leukemia risk. The laboratory data predicted 19 bands of the static field magnitude with a bandwidth of 9.1 μT that, together with 60 Hz magnetic fields, are expected to have biological activity. We then assessed the association between this exposure metric and childhood leukemia using data from a case-control study in Los Angeles County. ELF and static magnetic fields were measured in the bedrooms of 124 cases determined from a tumor registry and 99 controls drawn from friends and random digit dialing. Among these subjects, 26 cases and 20 controls were exposed to static magnetic fields lying in the predicted bands of biological activity centered at 38.0 μT and 50.6 μT. Although no association was found for childhood leukemia in relation to measured ELF or static magnetic fields alone, an increasing trend of leukemia risk with measured ELF fields was found for subjects within these static field bands (P for trend = 0.041). The odds ratio (OR) was 3.3 [95% confidence interval (CI) = 0.4–30.5] for subjects exposed to static fields within the derived bands and to ELF magnetic field above 0.30 μT (compared to subjects exposed to static fields outside the bands and ELF magnetic fields below 0.07 μT). When the 60 Hz magnetic fields were assessed according to the Wertheimer-Leeper code for wiring configurations, leukemia risks were again greater with the hypothesized exposure conditions (OR = 9.2 for very high current configurations within the static field bands: 95% CI = 1.3–64.6). Although the risk estimates are based on limited magnetic field measurements for a small number of subjects, these findings suggest that the risk of childhood leukemia may be related to the combined effects of the static and ELF magnetic fields. Further tests of the hypothesis are proposed. © 1995 Wiley-Liss, Inc.     

Influence of 50 Hz-1 mT magnetic field on human median nerve

In this study, human median nerve was exposed to power frequency magnetic fields in order to provide clarification for possibly changeable nerve conduction mechanism. The nerve was exposed to 50 Hz magnetic field by utilizing a special Helmholtz applicator. The experiments were carried out with six healthy human-volunteers. Median motor distal amplitude/proximal amplitude ratios were recorded from adult human median nerve pre-exposure, during, and post-exposure to a 50 Hz, 1 mT magnetic field. The result of 18 measurements shows that median motor distal amplitude/proximal amplitude ratio significantly decreases in pre-exposure state as compare to post exposure of which. The results of this study may be useful for some nerve rehabilitation, excitation, and stimulation in more effective/safe physical therapy. Additionally, 50 Hz, 1 mT sinusoidal magnetic field should not be recognizing as safe for conduction mechanism on a nerve. These mechanisms would be cleared by new advanced engineering models in other future works.