MRI magnetic field stimulates rotational sensors of the brain

Vertigo in and around magnetic resonance imaging (MRI) machines has been noted for years [1, 2]. Several mechanisms have been suggested to explain these sensations [3, 4], yet without direct, objective measures, the cause is unknown. We found that all of our healthy human subjects developed a robust nystagmus while simply lying in the static magnetic field of an MRI machine. Patients lacking labyrinthine function did not. We use the pattern of eye movements as a measure of vestibular stimulation to show that the stimulation is static (continuous, proportional to static magnetic field strength, requiring neither head movement nor dynamic change in magnetic field strength) and directional (sensitive to magnetic field polarity and head orientation). Our calculations and geometric model suggest that magnetic vestibular stimulation (MVS) derives from a Lorentz force resulting from interaction between the magnetic field and naturally occurring ionic currents in the labyrinthine endolymph fluid. This force pushes on the semicircular canal cupula, leading to nystagmus. We emphasize that the unique, dual role of endolymph in the delivery of both ionic current and fluid pressure, coupled with the cupula's function as a pressure sensor, makes magnetic-field-induced nystagmus and vertigo possible. Such effects could confound functional MRI studies of brain behavior, including resting-state brain activity.     

Thermoregulation in rodents exposed to high-intensity stationary magnetic fields

Rectal temperatures were recorded in mice and rats during exposure to a stationary 7.55 Tesla (1 T = 10(4) Gauss) homogeneous magnetic field, and to magnetic field gradients ranging from 58.1 - 58.6 T/m. Contrary to observations reported recently by other investigators, no evidence was found for a change in the body temperature of rodents exposed to strong homogeneous or gradient magnetic fields.     

On the Vertigo Due to Static Magnetic Fields

Vertigo is sometimes experienced in and around MRI scanners. Mechanisms involving stimulation of the vestibular system by movement in magnetic fields or magnetic field spatial gradients have been proposed. However, it was recently shown that vestibular-dependent ocular nystagmus is evoked when stationary in homogenous static magnetic fields. The proposed mechanism involves Lorentz forces acting on endolymph to deflect semicircular canal (SCC) cupulae. To investigate whether vertigo arises from a similar mechanism we recorded qualitative and quantitative aspects of vertigo and 2D eye movements from supine healthy adults (n = 25) deprived of vision while pushed into the 7T static field of an MRI scanner. Exposures were variable and included up to 135s stationary at 7T. Nystagmus was mainly horizontal, persisted during long-exposures with partial decline, and reversed upon withdrawal. The dominant vertiginous perception with the head facing up was rotation in the horizontal plane (85% incidence) with a consistent direction across participants. With the head turned 90 degrees in yaw the perception did not transform into equivalent vertical plane rotation, indicating a context-dependency of the perception. During long exposures, illusory rotation lasted on average 50 s, including 42 s whilst stationary at 7T. Upon withdrawal, perception re-emerged and reversed, lasting on average 30 s. Onset fields for nystagmus and perception were significantly correlated (p<.05). Although perception did not persist as long as nystagmus, this is a known feature of continuous SSC stimulation. These observations, and others in the paper, are compatible with magnetic-field evoked-vertigo and nystagmus sharing a common mechanism. With this interpretation, response decay and reversal upon withdrawal from the field, are due to adaptation to continuous vestibular input. Although the study does not entirely exclude the possibility of mechanisms involving transient vestibular stimulation during movement in and out of the bore, we argue these are less likely.     

A large-scale study on subjective perception of discomfort during 7 and 1.5 T MRI examinations

A study on subjective perception has been carried out in order to gain further insight into subjective discomfort and sensations experienced during 7 T magnetic resonance imaging (MRI). This study provides information about subjective acceptance, which is essential if 7 T MRI is to become a clinical diagnostic tool. Of 573 subjects who underwent 7 T MRI, 166 were also examined at 1.5 T, providing a means of discriminating field‐dependent discomfort. All subjects judged sources of discomfort and physiological sensations on an 11‐point scale (0 = no side effects, 10 = intolerable side effects) and scores were analyzed separately for exam phases, with and without table movement at each field strength. Results revealed that 7 T MRI was, in general, judged more uncomfortable than 1.5 T; however, most subjects rated the effects as being non‐critical (mean scores between 0.5 and 3.5). Significant differences were detected regarding vertigo and sweating between subjects positioned “head‐first” and “feet‐first” at 7 T (worse in “head‐first”) and between 7 and 1.5 T (worse at 7 T), with the effects being more pronounced in the moving compared to the stationary table position. The most unpleasant factor at 7 T was the extensive examination duration, while potentially field‐dependent sensations were rated less bothersome. In summary, our study indicates that although certain sensations increase at 7 T compared to 1.5 T, they are unlikely to hinder the use of 7 T MRI as a clinical diagnostic tool. Bioelectromagnetics. Bioelectromagnetics 32:610–619, 2011. © 2011 Wiley Periodicals, Inc.     

Numerical evaluation of the fields induced by body motion in or near high-field MRI scanners

In modern magnetic resonance imaging , both patients and health care workers are exposed to strong, non-uniform static magnetic fields inside and outside of the scanner, in which body movement may be able to induce electric currents in tissues which could be potentially harmful. This paper presents theoretical investigations into the spatial distribution of induced E-fields in a tissue-equivalent human model when moving at various positions around the magnet. The numerical calculations are based on an efficient, quasi-static, finite-difference scheme. Three-dimensional field profiles from an actively shielded 4 T magnet system are used and the body model projected through the field profile with normalized velocity. The simulation shows that it is possible to induce E-fields/currents near the level of physiological significance under some circumstances and provides insight into the spatial characteristics of the induced fields. The methodology presented herein can be extrapolated to very high field strengths for the evaluation of the effects of motion at a variety of field strengths and velocities.     

Activation changes in zebra finch (Taeniopygia guttata) brain areas evoked by alterations of the earth magnetic field

Many animals are able to perceive the earth magnetic field and to use it for orientation and navigation within the environment. The mechanisms underlying the perception and processing of magnetic field information within the brain have been thoroughly studied, especially in birds, but are still obscure. Three hypotheses are currently discussed, dealing with ferromagnetic particles in the beak of birds, with the same sort of particles within the lagena organs, or describing magnetically influenced radical-pair processes within retinal photopigments. Each hypothesis is related to a well-known sensory organ and claims parallel processing of magnetic field information with somatosensory, vestibular and visual input, respectively. Changes in activation within nuclei of the respective sensory systems have been shown previously. Most of these previous experiments employed intensity enhanced magnetic stimuli or lesions. We here exposed unrestrained zebra finches to either a stationary or a rotating magnetic field of the local intensity and inclination. C-Fos was used as an activity marker to examine whether the two treatments led to differences in fourteen brain areas including nuclei of the somatosensory, vestibular and visual system. An ANOVA revealed an overall effect of treatment, indicating that the magnetic field change was perceived by the birds. While the differences were too small to be significant in most areas, a significant enhancement of activation by the rotating stimulus was found in a hippocampal subdivision. Part of the hyperpallium showed a strong, nearly significant, increase. Our results are compatible with previous studies demonstrating an involvement of at least three different sensory systems in earth magnetic field perception and suggest that these systems, probably less elaborated, may also be found in nonmigrating birds.     

12T强静磁场对小鼠前庭系统及学习记忆能力的影响

目的:随着强静磁场的广泛应用,其生物安全性评估获得越来越多的关注。本文通过实验,评估强静磁场照射对小鼠前庭系统、学习记忆能力的影响及两者内在联系。方法:观察12T强静磁场照射2h条件下小鼠即时(2min内)效应和条件味觉厌恶反应情况,确定照射对小鼠前庭系统的影响;通过Y迷宫和Morris水迷宫实验,分析照射对小鼠学习记忆能力的影响。结果:研究发现照射后小鼠立即出现直立行为抑制、旋转平衡失调,以及持续10d的条件味觉厌恶反应,表明该照射对小鼠前庭系统造成了即时及持续影响。Y迷宫和Morris水迷宫分析结果表明照射后小鼠学习记忆能力未发生显著改变。结论:12T强静磁场2h照射对小鼠前庭系统存在显著影响和量效关系,照射可导致小鼠出现平衡失调,持续味觉厌恶的现象,但这种影响并非结构性或不可逆的,对小鼠学习记忆能力未造成影响。     

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.     

HCN Channels Are Not Required for Mechanotransduction in Sensory Hair Cells of the Mouse Inner Ear

The molecular composition of the hair cell transduction channel has not been identified. Here we explore the novel hypothesis that hair cell transduction channels include HCN subunits. The HCN family of ion channels includes four members, HCN1-4. They were orginally identified as the molecular correlates of the hyperpolarization-activated, cyclic nucleotide gated ion channels that carry currents known as I_f, I_Q or I_h. However, based on recent evidence it has been suggested that HCN subunits may also be components of the elusive hair cell transduction channel. To investigate this hypothesis we examined expression of mRNA that encodes HCN1-4 in sensory epithelia of the mouse inner ear, immunolocalization of HCN subunits 1, 2 and 4, uptake of the transduction channel permeable dye, FM1-43 and electrophysiological measurement of mechanotransduction current. Dye uptake and transduction current were assayed in cochlear and vestibular hair cells of wildtype mice exposed to HCN channel blockers or a dominant-negative form of HCN2 that contained a pore mutation and in mutant mice that lacked HCN1, HCN2 or both. We found robust expression of HCNs 1, 2 and 4 but little evidence that localized HCN subunits in hair bundles, the site of mechanotransduction. Although high concentrations of the HCN antagonist, ZD7288, blocked 50–70% of the transduction current, we found no reduction of transduction current in either cochlear or vestibular hair cells of HCN1- or HCN2- deficient mice relative to wild-type mice. Furthermore, mice that lacked both HCN1 and HCN2 also had normal transduction currents. Lastly, we found that mice exposed to the dominant-negative mutant form of HCN2 had normal transduction currents as well. Taken together, the evidence suggests that HCN subunits are not required for mechanotransduction in hair cells of the mouse inner ear.     

Mechanism of biological effects observed in honey bees (apis mellifera,L.) hived under extra-high-voltage transmission lines: Implications derived from bee exposure to simulated intense electric fields and shocks

This work explores mechanisms for disturbance of honey bee colonies under a 765 kV, 60-Hz transmission line [electric (E) field = 7 kV/m] observed in previous studies. Proposed mechanisms fell into two categories: direct bee perception of enhanced in-hive E fields and perception of shock from induced currents. The adverse biological effects could be reproduced in simulations where only the worker bees were exposed to shock or to E field in elongated hive entranceways (=tunnels). We now report the results of full-scale experiments using the tunnel exposure scheme, which assesses the contribution of shock and intense E field to colony disturbance. Exposure of worker bees (1,400 h) to 60-Hz E fields including 100 kV/m under moisture-free conditions within a nonconductive tunnel causes no deleterious affect on colony behavior. Exposure of bees in conductive (e.g., wet) tunnels produces bee disturbance, increased mortality, abnormal propolization, and possible impairment of colony growth. We propose that this substrate dependence of bee disturbance is the result of perception of shock from coupled body currents and enhanced current densities postulated to exist in the legs and thorax of bees on conductors. Similarly, disturbance occurs when bees are exposed to step-potential-induced currents. At 275–350 nA single bees are disturbed; at 600 nA bees begin abnormal propolization behavior; and stinging occurs at 900 nA. We conclude that biological effects seen in bee colonies under a transmission line are primarily the result of electric shock from induced hive currents. This evaluation is based on the limited effects of E-field exposure in tunnels, the observed disturbance thresholds caused by shocks in tunnels, and the ability of hives exposed under a transmission line to source currents 100–1,000 times the shock thresholds.     

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.     

Exposure to Strong Static Magnetic Fields Induces Hypoactivity in Weaning Mice

We studied the effects of a prolongued exposure to a strong (1.0 Tesla) static and uniform magnetic field upon the open field behaviour and body weight of weaning mice. We observed a marked reduction in the exploratory activity of mice exposed to the field relative to that of control animals kept in similar surroundings, and handled in the same way as the exposed mice. One week of continuous exposure to a 1.0 T field significantly reduces peripheral square entries (p<0.01) as well as rearings (p<0.05), but has no effect on body weight. Our findings agree with the suggestion that a strong magnetic field may act as stressing agent.     

Neurophysiology: vertigo in MRI machines

Subjects of brain-imaging studies often report experiencing vertigo while in MRI machines; a new study shows that the magnetic field stimulates the vestibular sensors in the inner ear by a Lorentz force.     

Quantitative characterization of the regulation of iron metabolism in glioblastoma stem-like cells using magnetophoresis

This study focuses on different iron regulation mechanisms of glioblastoma (GBM) cancer stem-like cells (CSCs) and non-stem tumor cells (NSTCs) using multiple approaches: cell viability, density, and magnetophoresis. GBM CSCs and NSTCs were exposed to elevated iron concentration, and their magnetic susceptibility was measured using single cell magnetophoresis (SCM), which tracks the magnetic and settling velocities of thousands of individual cells passing through the magnetic field with a constant energy gradient. Our results consistently demonstrate that GBM NSTCs have higher magnetic susceptibility distribution at increased iron concentration compared with CSCs, and we speculate that it is because CSCs have the ability to store a high amount of iron in ferritin, whereas the free iron ions inside the NSTCs lead to higher magnetic susceptibility and reduced cell viability and growth. Further, their difference in magnetic susceptibility has led us to pursue a separate experiment using a quadrupole magnetic separator (QMS), a novel microfluidic device that uses a concentric channel and permanent magnets in a special configuration to separate samples based on their magnetic susceptibilities. GBM CSCs and NSTCs were exposed to elevated iron concentration, stained with two different trackers, mixed and introduced into QMS; subsequently, the separated fractions were analyzed by fluorescent microscopy. The separation results portray a successful label-less magnetic separation of the two populations.     

Behavioral studies with mice exposed to DC and 60-Hz magnetic fields

Behavioral measures were evaluated in adult CD-1 and LAF-1 mice continuously exposed for 72 h to a 1.5-Tesla (1 T = 10(4) Gauss) homogeneous DC magnetic field, and in LAF-1 mice continuously exposed for 72 h to a sinusoidal 60-Hz, 1.65-mT (rms) homogeneous AC field. Three types of behavioral tests were employed: (1) Memory of an electroshock-motivated passive avoidance task was assessed in animals that had been trained immediately prior to the field exposure. The strength of memory was varied either by altering the strength of the electric footshock during training, or by administering a cerebral protein synthesis inhibitor, anisomycin, at the time of training. (2) General locomotor activity was measured using a quadrant-crossing test immediately after termination of the magnetic field exposure. (3) Sensitivity of the experimental subjects to the seizure-inducing neuropharmacological agent, pentylenetrazole , was assessed immediately after the field exposure on the basis of three criteria: (a) the percentage of subjects exhibiting a generalized seizure, (b) the mean time to seizure, and (c) the mean seizure level. The results of these studies revealed no behavioral alterations in exposed mice relative to controls in any of the experimental tests with the 1.5-T DC field or the 60-Hz, 1.65-mT (rms) AC field.     

Evaluation in humans of ELF-EMF exposure on chromogranin A,a marker of neuroendocrine tumors and stress

ABSTRACT

Chromogranin A (CgA), which is a major protein in adrenal chromaffin cells and adrenergic neurons, is a clinically relevant endocrine and neuroendocrine tumor marker including pheochromocytomas, neuroblastomas, and related neurogenic tumors. In this study, we looked at the effect in humans of chronic daily exposure to a 50-Hz magnetic field. We examined in 15 men (38.0 ± 0.9 years) the effects of chronic daily exposure to a 50-Hz magnetic field for 1–20 yrs both at home and at work. EMDEX II dosimeters were used to record magnetic field all day long every 30 s. for 1 week. The weekly geometric mean of the individual exposures ranged from 0.1 to 2.6 μT. Blood samples were taken hourly between 20:00 h and 08:00 h. CgA patterns of exposed subjects were compared to age-matched controls. The results of exposed subjects were compared with those for 15 unexposed men who served as controls and whose individual exposure was ten times lower ranging from 0.004 to 0.092 μT. This work shows that in the control group the serum CgA levels exhibited a nighttime peak with a progressive decline of the serum concentrations and a nadir in the morning. Both the profile and the serum concentrations of CgA, a marker of neuroendocrine tumors and stress, did not appear to be impaired in the subjects chronically exposed over a long period (up to 20 yrs) to magnetic fields though a trend toward lower levels were found at the highest exposure (>0.3 μT). This does not rule out, however, that the potential deleterious risk of ELF-EMF on frail populations such as children and the elderly may be greater at low exposure and should hence be documented, at least for their residential exposure.     

Behavioural evidence that magnetic field effects in the land snail,Cepaea nemoralis,might not depend on magnetite or induced electric currents

Although extremely low frequency (ELF) magnetic fields (<300 Hz) appear to exert a variety of biological effects, the magnetic field sensing/transduction mechanism(s) remains to be established. Here, using the inhibitory effects of magnetic fields on endogenous opioid peptide-mediated “analgaesic” response of the land snail. Cepaea nemoralis, we addressed the mechanism(s) of action of ELF magnetic fields. Indirect mechanisms involving both induced electric fields and direct magnetic field detection mechanisms (e.g., magnetite, parametric resonance) were evaluated. Snails were exposed to a static magnetic field (B_DC=78±1 μT) and to a 60 Hz magnetic field (B_AC=299±1 μT peak) with the angle between the static and 60 Hz magnetic fields varied in eight steps between 0° and 90°. At 0° and 90°, the magnetic field reduced opioid-induced analgaesia by approximately 20%, and this inhibition was increased to a maximum of 50% when the angle was between 50° and 70°. Because B_AC was fixed in amplitude, direction, and frequency, any induced electric currents would be constant independent of the B_AC/B_DC angle. Also, an energy transduction mechanism involving magnetite should show greatest sensitivity at 90°. Therefore, the energy transduction mechanism probably does not involve induced electric currents or magnetite. Rather, our results suggest a direct magnetic field detection mechanism consistent with the parametric resonance model proposed by Lednev. © 1996 Wiley-Liss, Inc.     

Being Moved by the Self and Others: Influence of Empathy on Self-Motion Perception

Background

The observation of conspecifics influences our bodily perceptions and actions: Contagious yawning, contagious itching, or empathy for pain, are all examples of mechanisms based on resonance between our own body and others. While there is evidence for the involvement of the mirror neuron system in the processing of motor, auditory and tactile information, it has not yet been associated with the perception of self-motion.

Methodology/Principal Findings

We investigated whether viewing our own body, the body of another, and an object in motion influences self-motion perception. We found a visual-vestibular congruency effect for self-motion perception when observing self and object motion, and a reduction in this effect when observing someone else''s body motion. The congruency effect was correlated with empathy scores, revealing the importance of empathy in mirroring mechanisms.

Conclusions/Significance

The data show that vestibular perception is modulated by agent-specific mirroring mechanisms. The observation of conspecifics in motion is an essential component of social life, and self-motion perception is crucial for the distinction between the self and the other. Finally, our results hint at the presence of a “vestibular mirror neuron system”.     

A STUDY OF THE EFFECTS OF STATIC AND EXTREMELY LOW FREQUENCY MAGNETIC FIELDS ON LIPID PEROXIDATION PRODUCTS IN SUBCELLULAR FIBROBLAST FRACTIONS

Cultured fibroblasts isolated from murine livers by tissue trypsinization were exposed to a static magnetic field (0.490 T) and to extremely low frequency (ELF) magnetic field (50 Hz, 0.020 T). The cultures were exposed to magnetic fields on four consecutive days for exposure times of 2, 4, 8, 16, 32, and 64 min. After such exposures and obtaining of fibroblast subcellular fractions, lipid peroxidation product—malondialdehyde (MDA) was measured. Increased peroxidation of fibroblasts' membrane structures exposed to an ELF magnetic field was observed in subcellular fractions—microsomal, mitochondrial, and nuclear. No changes in peroxidation of membrane structures were found in fibroblasts exposed to a static magnetic field.     

Project NEMESIS: perception of a 50 Hz electric and magnetic field at low intensities (laboratory experiment).

The Electrical Hypersensitivity Syndrome (EHS) is a condition where people suffer from various nonspecific health symptoms attributed to an assumed adverse effect of electric and magnetic fields (EMF). Many EHS patients report the ability to consciously perceive EMF at very low intensities. The existence of a direct EMF perception could be the key to explain at least partially the aetiology of EHS through stress mechanisms and allow the comparison with well known environmental stressors such as noise or odor. The double blind laboratory experiment tested the hypothesis that there are subjects with the ability to perceive 50 Hz EMF at 100 V/m and 6 microT (EMF sensitive) and to investigate the prevalence of EMF sensitivity in a group consisting of subjects with or without self-reported EHS. A total of 63 volunteers, 49 with EHS and 14 controls, took part in the EMF perception experiment, where 10 sham and 10 exposed 2 min blocks had to be judged in randomized sequence (field on/field off). Seven out of 63 subjects reached a statistically significant result which points to the existence of a small EMF sensitive subgroup within the study group. There was no relevant difference between the subjects with self reported EHS and those without in terms of the success rate in the field perception experiment, as well as the number and types of symptoms encountered during the test. The results of the EMF perception experiment suggest that EHS is not a prerequisite for the ability to consciously perceive weak EMF and vice versa.