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Magnetic Therapy Research: Neurological Effects of Magnetic Fields

Static Magnetic Fields and PEMF


Transcranial Magnetic Stimulation


Complementary therapies for neuropathic and neuralgic pain: systematic review.

Pittler MH, Ernst E.

Complementary Medicine, Peninsula Medical School, Universities of Exeter and Plymouth, Exeter, UK.

OBJECTIVE: To assess the evidence from rigorous clinical trials, systematic reviews, and meta-analyses of complementary and alternative therapies for treating neuropathic and neuralgic pain.

METHODS: Systematic searches were carried out in the databases Medline, Embase, Amed, Scopus, the Cochrane Database of Systematic Reviews, Natural Standard, and the Natural Medicines Comprehensive Database. Each database was searched from its respective inception until March 2006. To be included, trials were required to state that they were randomized. Systematic reviews and meta-analyses were included if based on the results of randomized trials. No language restrictions were imposed.

RESULTS: Five relevant systematic reviews and meta-analyses and 15 additional trials met the inclusion criteria and were reviewed. Data on the following complementary and alternative medicine treatments were identified: acupuncture, electrostimulation, herbal medicine, magnets, dietary supplements, imagery, and spiritual healing.

CONCLUSIONS: On the basis of our findings, the evidence is not fully convincing for most complementary and alternative medicine modalities in relieving neuropathic or neuralgic pain. However, for topically applied capsaicin there is evidence of effectiveness beyond placebo. The evidence can be classified as encouraging and warrants further study for cannabis extract, magnets, carnitine, and electrostimulation.

The Clinical Journal of Pain. 2008 October. 24 (8):731-3. PMID: 18806539

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Peripheral neuropathy: pathogenic mechanisms and alternative therapies.

Head KA.
Thorne Research, Inc., PO Box 25, Dover, ID 83825, USA.

Peripheral neuropathy (PN), associated with diabetes, neurotoxic chemotherapy, human immunodeficiency virus (HIV)/antiretroviral drugs, alcoholism, nutrient deficiencies, heavy metal toxicity, and other etiologies, results in significant morbidity.

Conventional pain medications primarily mask symptoms and have significant side effects and addiction profiles. However, a widening body of research indicates alternative medicine may offer significant benefit to this patient population.

Alpha-lipoic acid, acetyl-L-carnitine, benfotiamine, methylcobalamin, and topical capsaicin are among the most well-researched alternative options for the treatment of PN. Other potential nutrient or botanical therapies include vitamin E, glutathione, folate, pyridoxine, biotin, myo-inositol, omega-3 and -6 fatty acids, L-arginine, L-glutamine, taurine, N-acetylcysteine, zinc, magnesium, chromium, and St. John's wort.

In the realm of physical medicine, acupuncture, magnetic therapy, and yoga have been found to provide benefit. New cutting-edge conventional therapies, including dual-action peptides, may also hold promise.

Head KA (December 2006). "Peripheral neuropathy: pathogenic mechanisms and alternative therapies." Alternative Medicine Review: A Journal of Clinical Therapeutic. 11(4):294-329. PMID: 17176168

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Static magnetic field influence on rat brain function detected by heart rate monitoring.

Veliks V, Ceihnere E, Svikis I, Aivars J.

Faculty of Biology, University of Latvia, Riga, Latvia.

The aim of the present study was to identify the effects of a static magnetic field (SMF) on rat brain structures that control autonomic functions, specifically heart rate and heart rhythmicity. The experiments were carried out on 44 male Wistar rats under ketamine-xylazine anesthesia. SMF was induced using samarium-cobalt fused magnets (20 x 20 x 10 mm in size) placed bitemporally. Magnetic induction intensity was 100 mT on the surface of the head. Duration of magnetic field application was 15 min. An electrocardiogram was recorded from limb lead II, and both heart rate (average duration of cardiac cycles) and heart rhythmicity were analyzed before and after SMF application. SMF evoked changes in both heart rate and rhythm in 80% of the animals; the predominant effects were bradycardia and disappearance of respiratory sinus arrhythmia. However, the effectiveness of SMF in large measure depends on both functional peculiarities and functional activities of brain autonomic centers. Bioelectromagnetics 25:211-215, 2004. Copyright 2004 Wiley-Liss, Inc.

Bioelectromagnetics. 2004 Apr;25(3):211-5.

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Pulsed magnetic field therapy in refractory neuropathic pain secondary to peripheral neuropathy: electrodiagnostic parameters - pilot study.

Weintraub MI, Cole SP.

New York Medical College, Briarcliff Manor, New York 10510, USA.

CONTEXT: Neuropathic pain (NP) from peripheral neuropathy (PN) arises from ectopic firing of unmyelinated C-fibers with accumulation of sodium and calcium channels. Because pulsed electromagnetic fields (PEMF) safely induce extremely low frequency (ELF) quasirectangular currents that can depolarize, repolarize, and hyperpolarize neurons, it was hypothesized that directing this energy into the sole of one foot could potentially modulate neuropathic pain.

OBJECTIVE: To determine if 9 consecutive 1-h treatments in physician's office (excluding weekends) of a pulsed signal therapy can reduce NP scores in refractory feet with PN.

DESIGN/SETTING/PATIENTS: 24 consecutive patients with refractory and symptomatic PN from diabetes, chronic inflammatory demyelinating polyneuropathy (CIDP), pernicious anemia, mercury poisoning, paraneoplastic syndrome, tarsal tunnel, and idiopathic sensory neuropathy were enrolled in this nonplacebo pilot study. The most symptomatic foot received therapy. Primary endpoints were comparison of VAS scores at the end of 9 days and the end of 30 days follow-up compared to baseline pain scores. Additionally, Patients' Global Impression of Change (PGIC) questionnaire was tabulated describing response to treatment. Subgroup analysis of nerve conduction scores, quantified sensory testing (QST), and serial examination changes were also tabulated. Subgroup classification of pain (Serlin) was utilized to determine if there were disproportionate responses.

INTERVENTION: Noninvasive pulsed signal therapy generates a unidirectional quasirectangular waveform with strength about 20 gauss and a frequency about 30 Hz into the soles of the feet for 9 consecutive 1-h treatments (excluding weekends). The most symptomatic foot of each patient was treated.

RESULTS: All 24 feet completed 9 days of treatment. 15/24 completed follow-up (62%) with mean pain scores decreasing 21% from baseline to end of treatment (P=0.19) but with 49% reduction of pain scores from baseline to end of follow-up (P<0.01). Of this group, self-reported PGIC was improved 67% (n=10) and no change was 33% (n=5). An intent-to-treat analysis based on all 24 feet demonstrated a 19% reduction in pain scores from baseline to end of treatment (P=0.10) and a 37% decrease from baseline to end of follow-up (P<0.01). Subgroup analysis revealed 5 patients with mild pain with nonsignificant reduction at end of follow-up. Of the 19 feet with moderate to severe pain, there was a 28% reduction from baseline to end of treatment (P<0.05) and a 39% decrease from baseline to end of follow-up (P<0.01). Benefit was better in those patients with axonal changes and advanced CPT baseline scores. The clinical examination did not change. There were no adverse events or safety issues.

CONCLUSIONS: These pilot data demonstrate that directing PEMF to refractory feet can provide unexpected shortterm analgesic effects in more than 50% of individuals. The role of placebo is not known and was not tested. The precise mechanism is unclear yet suggests that severe and advanced cases are more magnetically sensitive. Future studies are needed with randomized placebo-controlled design and longer treatment periods.

Neurorehabil Neural Repair. 2004 Mar;18(1):42-6.

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Attention to features precedes attention to locations in visual search: evidence from electromagnetic brain responses in humans.

Hopf JM, Boelmans K, Schoenfeld MA, Luck SJ, Heinze HJ.

Department of Neurology II, Otto-von-Guericke-University, D-39120 Magdeburg, Germany.

Single-unit recordings in macaque extrastriate cortex have shown that attentional selection of nonspatial features can operate in a location-independent manner. Here, we investigated analogous neural correlates at the neural population level in human observers by using simultaneous event-related potential (ERP) and event-related magnetic field (ERMF) recordings. The goals were to determine (1) whether task-relevant features are selected before attention is allocated to the location of the target, and (2) whether this selection reflects the locations of the relevant features. A visual search task was used in which the spatial distribution of nontarget items with attended feature values was varied independently of the location of the target. The presence of task-relevant features in a given location led to a change in ERP/ERMF activity beginning approximately 140 msec after stimulus onset, with a neural origin in the ventral occipito-temporal cortex. This effect was independent of the location of the actual target. This effect was followed by lateralized activity reflecting the allocation of attention to the location of the target (the well known N2pc component), which began at approximately 170 msec poststimulus. Current source localization indicated that the allocation of attention to the location of the target originated in more anterior regions of occipito-temporal cortex anterior than the feature-related effects. These findings suggest that target detection in visual search begins with the detection of task-relevant features, which then allows spatial attention to be allocated to the location of a likely target, which in turn allows the target to be positively identified.

J Neurosci. 2004 Feb 25;24(8):1822-32.

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Identifiable neurons inhibited by Earth-strength magnetic stimuli in the mollusc Tritonia diomedea.

Wang JH, Cain SD, Lohmann KJ.

Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA Friday Harbor Laboratories, University of Washington, Friday Harbor, Washington 98250, USA.

Diverse animals use the Earth's magnetic field as an orientation cue, but little is known about the sensory, processing and motor elements of the neural circuitry underlying magnetic orientation behavior. The marine mollusc Tritonia diomedea has both a magnetic compass sense and a simple nervous system accessible to electrophysiological analysis. Previous studies have revealed that four identifiable neurons, known as LPd5, RPd5, LPd6 and RPd6, respond with enhanced electrical activity to changes in Earth-strength magnetic fields. Here we report that two additional neurons, LPd7 and RPd7, are inhibited by magnetic stimuli. Cobalt fills of the Pd7 neurons indicated that two prominent neurites emerge from the soma and project to the periphery through the ipsilateral cerebral nerves CeN6 and CeN3; in some cases, a third neurite was visible in CeN2. The nerves extend to the anterior region of the animal where they innervate the lateral body walls, oral veil and mouth region. Action potentials in the Pd7 neurons propagate from the central ganglia toward the periphery. Thus, the Pd7 cells have characteristics of efferent neurons. The precise function of these cells during magnetic orientation behavior, however, remains to be determined.

J Exp Biol. 2004 Feb 22;207(Pt 6):1043-9.

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Peripheral nerve magnetic stimulation: influence of tissue non-homogeneity.

Krasteva VT, Papazov SP, Daskalov IK.

BACKGROUND: Peripheral nerves are situated in a highly non-homogeneous environment, including muscles, bones, blood vessels, etc. Time-varying magnetic field stimulation of the median and ulnar nerves in the carpal region is studied, with special consideration of the influence of non-homogeneities.

METHOD: A detailed three-dimensional finite element model (FEM) of the anatomy of the wrist region was built to assess the induced currents distribution by external magnetic stimulation. The electromagnetic field distribution in the non-homogeneous domain was defined as an internal Dirichlet problem using the finite element method. The boundary conditions were obtained by analysis of the vector potential field excited by external current-driven coils.

RESULTS: The results include evaluation and graphical representation of the induced current field distribution at various stimulation coil positions. Comparative study for the real non-homogeneous structure with anisotropic conductivities of the tissues and a mock homogeneous media is also presented. The possibility of achieving selective stimulation of either of the two nerves is assessed.

CONCLUSION: The model developed could be useful in theoretical prediction of the current distribution in the nerves during diagnostic stimulation and therapeutic procedures involving electromagnetic excitation. The errors in applying homogeneous domain modeling rather than real non-homogeneous biological structures are demonstrated. The practical implications of the applied approach are valid for any arbitrary weakly conductive medium.

Biomed Eng Online. 2003 Dec 23; 2(1): 19.

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Control of orientation of rat Schwann cells using an 8-T static magnetic field.

Eguchi Y, Ogiue-Ikeda M, Ueno S.

Department of Biomedical Engineering, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

Schwann cells aid in neuronal regeneration in the peripheral nervous system via guiding the regrowth of axons. In this study, we investigated the magnetic orientation of Schwann cells, and of a mixture of Schwann cells and collagen, after an 8-tesla magnetic field exposure. We obtained cultured Schwann cells from dissected sciatic nerves of neonatal rats. After 60 h of magnetic field exposure, Schwann cells oriented parallel to the magnetic fields. In contrast, the mixture of Schwann cells and collagen, Schwann cells oriented in the direction perpendicular to the magnetic field after 2 h of magnetic field exposure. In this case, Schwann cells aligned along the collagen fiber oriented by magnetic fields. The magnetic control of Schwann cell alignment is useful in medical engineering applications such as nerve regeneration.

Neurosci Lett. 2003 Nov 13;351(2):130-2.

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Use of low-power electromagnetic therapy in diabetic polyneuropathy.

Chebotar'ova LL, Chebotar'ov HIe.

The clinical-electroneuromyography investigations were performed for objective evaluation of low-power electromagnetic therapy effectiveness in 12 patients with diabetic polyneuropaties. It is established that combination of low-power electromagnetic therapy using "ANET-UHF", "ANET-SHF" apparatus (Ukraine) and low-power variable magnetic field using AMT apparatus (Ukraine) give the stable positive effects. The positive changes were confirmed by following: the decrease of neurological deficit and required insulin daily dose, nerve conduction velocity increase, increase of the muscle compound action potentials (muscle power) and peripheral outflow in some patients.

Fiziol Zh. 2003;49(2):85-90.

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Neuronal ion channels and their sensitivity to extremely low frequency weak electric field effects.

Mathie A, Kennard LE, Veale EL.

Biophysics Section, Department of Biological Sciences, Imperial College London, London SW7 2AZ, UK.

Neuronal ion channels are gated pores whose opening and closing is usually regulated by factors such as voltage or ligands. They are often selectively permeable to ions such as sodium, potassium or calcium. Rapid signalling in neurons requires fast voltage sensitive mechanisms for closing and opening the pore. Anything that interferes with the membrane voltage can alter channel gating and comparatively small changes in the gating properties of a channel can have profound effects. Extremely low frequency electrical or magnetic fields are thought to produce, at most, microvolt changes in neuronal membrane potential. At first sight, such changes in membrane potential seem orders of magnitude too small to significantly influence neuronal signalling. However, in the central nervous system, a number of mechanisms exist which amplify signals. This may allow such small changes in membrane potential to induce significant physiological effects.

Radiat Prot Dosimetry. 2003; 106(4): 311-6.

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The study of effects of static magnetic field on SP-mRNA in trigeminal ganglion in rats.

Chang X, Qin K, Lu Y.

Faculty of Stomatology, China Medical University, Shenyang 110002, China.

OBJECTIVE: To evaluate the effect of static magnetic field on the expression of SP-mRNA in TG in rats.

METHODS: 44 Wistar rats aged 6-7 weeks were put into static magnetic field and were sacrificed at 1 h, 2 h, 6 h, 12 h, 24 h, respectively. In situ hybridization method was used to evaluate the changes of SP-mRNA expression at different time point.

RESULTS: Many neurons in TG were marked with SP probes in each group, the expression of SP-mRNA increased remarkably in static magnetic field group. In this group, the percentage of SP-mRNA positive neurons in TG increased greatly in 1 h, reached its peak in 2 h, from then on, decrease of the percentage started slowly but a moderate percentage was kept until 24 h, which was thought to be enough to maintain orthodontic tooth movement. The tendency of control group was almost the same with that of experimental group. The expression of SP-mRNA was higher in experimental group within 2 h but became lower after 2 h as compared with control group, this indicated that magnetic field reduced the SP-mRNA expression and exerted restoring effect on trauma. There were significant differences between experimental groups and control group at different time points (P < 0.01).

CONCLUSION: The expression of SP-mRNA in TG in rats increased significantly in static magnetic field.

Hua Xi Kou Qiang Yi Xue Za Zhi. 2003 Jun;21(3):235-7.

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On the applicability of two different stimulation techniques for intra-operative peroneal nerve conduction testing.

Nebelung W, Wissel H, Awiszus F.

Neuromuscular Research Group, Otto-von Guericke-University Magdeburg, Clinic for Orthopedic Surgery, Germany.

Dysfunction of the peroneal nerve is an important complication of knee surgery. We compared two monitoring procedures of peroneal nerve function during a standardized operation, a closing wedge high tibial osteotomy. For two types of stimulation the evoked compound motor unit action potentials (CMAPs) were recorded on the tibialis anterior muscle. We used direct perineural electrical stimulation of the common peroneal nerve distal to the cuff (dCMAPs) after nerve identification in the surgical field. Additionally, magnetic stimulation of the sacral plexus proximal to the cuff (pCMAPs) was performed. It was found that dCMAPs were recorded during almost one hour of tourniquet time whereas the pCMAPs were blocked after 25-30 min in 9 out of 11 cases. On the other hand, the CMAP obtained after proximal stimulation exhibited a latency shift with tourniquet yielding an indicator of ischaemic changes present beneath and distal to the tourniquet cuff. In conclusion, different applicabilities of both stimulation techniques under tourniquet conditions were demonstrated.

J Orthop Res. 2001 Jan;19(1):160-5.

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Threshold and limits of magnetic field action at the presynaptic membrane.

Rosen AD.

Department of Neurology, School of Medicine, State University of New York at Stony Brook 11794-8121.

The relationship of field intensity and exposure duration to the inhibitory effect of static magnetic fields on presynaptic membrane function was examined in order to further define the mechanism of action of these fields. Miniature endplate potentials (MEPPs) were recorded from the isolated murine neuromuscular junction, maintained at a temperature of 35.5 degrees C, during exposure to static magnetic fields of varying duration and intensity. Inhibition of MEPP generation correlated well with the product of the square of the flux density and exposure time. At lower product values the relationship was linear with an absolute flux density threshold of 37.9 mT. Higher product values were associated with deviation from linearity indicative of a limit on the extent of inhibition. These findings are consistent with the hypothesis that static magnetic fields induce a reorientation of diamagnetic molecular domains within the membrane but with a restriction on the degree of reorientation imposed by the membrane's cytoskeleton.

Biochim Biophys Acta. 1994 Jul 13;1193(1):62-6.

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Effect of weak, pulsing electromagnetic fields on neural regeneration in the rat.

Ito H, Bassett CA.

The short- and long-term effects of pulsed electromagnetic fields (PEMFs) on the rate and quality of peripheral nerve regeneration were studied. High bilateral transections of rat sciatic nerves were surgically approximated (a 1-mm gap was left) and shielded with a Silastic sleeve. Animals were exposed to PEMFs for two to 14 weeks after operation. Three groups of 20 rats each (control rats and rats undergoing 12- and 24-hour/day PEMF exposure) were killed at two weeks. Histologically, regenerating axons had penetrated the distal stump nearly twice as far in the PEMF-exposed animals as in the control animals. Return of motor function was judged two to 14 weeks after operation by the load cell-measured, plantar-flexion force produced by neural stimulation proximal to the transection site. Motor function returned earlier in experimental rats and to significantly higher load levels than in control rats. Nerves from animals functioning 12-14 weeks after operation had less interaxonal collagen, more fiber-containing axis cylinders, and larger fiber diameters in the PEMF-exposed group than in the control rats. Histologic and functional data indicate that PEMFs improve the rate and quality of peripheral nerve regeneration in the severed rat sciatic nerve by a factor of approximately two.

Clin Orthop. 1983 Dec;(181):283-90.

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Effects of high-peak pulsed electromagnetic field on the degeneration and regeneration of the common peroneal nerve in rats.

Raji AR, Bowden RE.

Apart from preliminary notices of present work, previous reports of experimental and clinical trials of the effects of a high-peak pulsed electromagnetic field (PEMF) on degeneration and regeneration of peripheral nerves lacked statistical analysis. Therefore, we designed experiments with standardised operative, histological, cytological and morphometric techniques to assess the effect of PEMF on lesions of the common peroneal nerves in paired male rats matched for age, environmental conditions and level and type of lesion. One of two types of lesion was induced in the left common peroneal nerve: in 12 pairs of rats the nerve was crushed just above the knee and in the remaining 12 pairs the nerve was cut and immediately sutured at the same level. The right common peroneal nerve of each rat served as a control. Animals received 15 minutes of PEMF produced by a Diapulse machine or sham treatment daily for periods ranging from three and a half days to eight weeks after injury. Healthy nerves were unaffected, but after damage there were statistically significant differences between PEMF treated and sham treated rats. PEMF accelerated the recovery of injured limbs and the degeneration, regeneration and maturation of myelinated axons; epineural, perineural and intraneural fibrosis was reduced; and the luminal cross-sectional area of intraneural vessels increased after both types of lesion. Findings are discussed and the need for clinical trials is stressed.

J Bone Joint Surg Br. 1983 Aug;65(4):478-92.

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The effect of stimulus intensity on brain responses evoked by transcranial magnetic stimulation.

Komssi S, Kahkonen S, Ilmoniemi RJ.

BioMag Laboratory, Engineering Centre, Helsinki University Central Hospital, Helsinki, Finland.

To better understand the neuronal effects of transcranial magnetic stimulation (TMS), we studied how the TMS-evoked brain responses depend on stimulation intensity. We measured electroencephalographic (EEG) responses to motor-cortex TMS, estimated the intensity dependence of the overall brain response, and compared it to a theoretical model for the intensity dependence of the TMS-evoked neuronal activity. Left and right motor cortices of seven volunteers were stimulated at intensities of 60, 80, 100, and 120% of the motor threshold (MT). A figure-of-eight coil (diameter of each loop 4 cm) was used for focal stimulation. EEG was recorded with 60 scalp electrodes. The intensity of 60% of MT was sufficient to produce a distinct global mean field amplitude (GMFA) waveform in all subjects. The GMFA, reflecting the overall brain response, was composed of four peaks, appearing at 15 +/- 5 msec (Peak I), 44 +/- 10 msec (II), 102 +/- 18 msec (III), and 185 +/- 13 msec (IV). The peak amplitudes depended nonlinearly on intensity. This nonlinearity was most pronounced for Peaks I and II, whose amplitudes appeared to sample the initial part of the sigmoid-shaped curve modeling the strength of TMS-evoked neuronal activity. Although the response amplitude increased with stimulus intensity, scalp distributions of the potential were relatively similar for the four intensities. The results imply that TMS is able to evoke measurable brain activity at low stimulus intensities, probably significantly below 60% of MT. The shape of the response-stimulus intensity curve may be an indicator of the activation state of the brain. Copyright 2004 Wiley-Liss, Inc.

Hum Brain Mapp. 2004 Mar;21(3):154-64.

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Repetitive transcranial magnetic stimulation improves open field locomotor recovery after low but not high thoracic spinal cord compression-injury in adult rats.

Poirrier AL, Nyssen Y, Scholtes F, Multon S, Rinkin C, Weber G, Bouhy D, Brook G, Franzen R, Schoenen J.

Research Centre for Cellular and Molecular Neurobiology, Neuroanatomy Laboratory, University of Liege, Belgium.

Electromagnetic fields are able to promote axonal regeneration in vitro and in vivo. Repetitive transcranial magnetic stimulation (rTMS) is used routinely in neuropsychiatric conditions and as an atraumatic method to activate descending motor pathways. After spinal cord injury, these pathways are disconnected from the spinal locomotor generator, resulting in most of the functional deficit. We have applied daily 10 Hz rTMS for 8 weeks immediately after an incomplete high (T4-5; n = 5) or low (T10-11; n = 6) thoracic closed spinal cord compression-injury in adult rats, using 6 high- and 6 low-lesioned non-stimulated animals as controls. Functional recovery of hindlimbs was assessed using the BBB locomotor rating scale. In the control group, the BBB score was significantly better from the 7th week post-injury in animals lesioned at T4-5 compared to those lesioned at T10-11. rTMS significantly improved locomotor recovery in T10-11-injured rats, but not in rats with a high thoracic injury. In rTMS-treated rats, there was significant positive correlation between final BBB score and grey matter density of serotonergic fibres in the spinal segment just caudal to the lesion. We propose that low thoracic lesions produce a greater functional deficit because they interfere with the locomotor centre and that rTMS is beneficial in such lesions because it activates this central pattern generator, presumably via descending serotonin pathways. The benefits of rTMS shown here suggest strongly that this non-invasive intervention strategy merits consideration for clinical trials in human paraplegics with low spinal cord lesions. Copyright 2003 Wiley-Liss, Inc.

J Neurosci Res. 2004 Jan 15; 75(2): 253-61.

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Acute remapping within the motor system induced by low-frequency repetitive transcranial magnetic stimulation.

Lee L, Siebner HR, Rowe JB, Rizzo V, Rothwell JC, Frackowiak RS, Friston KJ.

Wellcome Department of Imaging Neuroscience, Institute of Neurology, University College London, London, WC1N 3BG United Kingdom.

Repetitive transcranial magnetic stimulation (rTMS) of human primary motor cortex (M1) changes cortical excitability at the site of stimulation and at distant sites without affecting simple motor performance. The aim of this study was to explore how rTMS changes regional excitability and how the motor system compensates for these changes. Using functional brain imaging, activation was mapped at rest and during freely selected finger movements after 30 min of 1 Hz rTMS. rTMS increased synaptic activity in the stimulated left M1 and induced widespread changes in activity throughout areas engaged by the task. In particular, movement-related activity in the premotor cortex of the nonstimulated hemisphere increased after 1 Hz rTMS. Analyses of effective connectivity confirmed that the stimulated part of M1 became less responsive to input from premotor and mesial motor areas. Conversely, after rTMS our results were consistent with increased coupling between an inferomedial portion of left M1 and anterior motor areas. These results are important for three reasons. First, they show changes in motor excitability to central inputs from other cortical areas (as opposed to peripheral or exogenous inputs used in previous studies). Second, they suggest that maintenance of task performance may involve activation of premotor areas contralateral to the site of rTMS, similar to that seen in stroke patients. Third, changes in motor activations at the site of rTMS suggest an rTMS-induced remodeling of motor representations during movement. This remapping may provide a neural substrate for acute compensatory plasticity of the motor system in response to focal lesions such as stroke.

J Neurosci. 2003 Jun 15;23(12):5308-18.

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Transcranial magnetic stimulation in neurology.

Kobayashi M, Pascual-Leone A.

Laboratory for Magnetic Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.

Transcranial magnetic stimulation (TMS) is a non-invasive tool for the electrical stimulation of neural tissue, including cerebral cortex, spinal roots, and cranial and peripheral nerves. TMS can be applied as single pulses of stimulation, pairs of stimuli separated by variable intervals to the same or different brain areas, or as trains of repetitive stimuli at various frequencies. Single stimuli can depolarise neurons and evoke measurable effects. Trains of stimuli (repetitive TMS) can modify excitability of the cerebral cortex at the stimulated site and also at remote areas along functional anatomical connections. TMS might provide novel insights into the pathophysiology of the neural circuitry underlying neurological and psychiatric disorders, be developed into clinically useful diagnostic and prognostic tests, and have therapeutic uses in various diseases. This potential is supported by the available studies, but more work is needed to establish the role of TMS in clinical neurology.

Lancet Neurol. 2003 Mar;2(3):145-56.

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Low-rate repetitive TMS allays central pain.

Canavero S, Bonicalzi V, Dotta M, Vighetti S, Asteggiano G.

Pain Relief Unit, Department of Neurosciences, Molinette Hospital, Turin, Italy.

Only about 50% of central pain patients respond to motor cortex stimulation in the long run. There is a need for prognostic factors. Here we show that propofol test and TMS both predict short-term effect in nine patients with central pain. This may help reduce the number of failures.

Neurol Res. 2003 Mar;25(2):151-2.

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A clinical study on the magnetic stimulation of the facial nerve.

Yamakawa T, Yoshikawa H, Arai A, Miyazaki T, Ichikawa G.

Department of Otorhinolaryngology, Juntendo University, School of Medicine, Tokyo, Japan.

OBJECTIVES: A clinical study on the usefulness of magnetic stimulation of the facial nerve, with special attention paid to the selection of the coil shape and stimulation procedures.

STUDY DESIGN: The subjects consisted of 55 patients with Bell's palsy, 1 patient with a cerebellopontine angle (CPA) tumor, 1 patient with multiple sclerosis (MS), and 30 normal subjects. Three types of coils were used in this study; a 90-mm large single coil, a 40-mm small single coil, and a 20-mm small double coil.

METHODS: The compound muscle action potentials (CMAPs) and long latency response were evoked by transcranial magnetic stimulation (TMS) with a 90-mm large single coil. The 40-mm small single coil was used to test blink reflex by aiming it at the supraorbital nerve as the target site. The subcutaneous activation of the infra-auricular facial nerve was performed with the 20-mm double coil.

RESULTS: The reproducible CMAP and long latency responses were obtained from normal subjects with TMS. However, responses were observed only in patients with relatively mild Bell's palsy. The magnetic stimulation-evoked responses reflected the brainstem function in the patients with a CPA tumor and MS.

CONCLUSION: Although magnetic stimulation remains inferior to conventional electric stimulation in some sense and requires further study, this method is potentially useful because it can stimulate the facial nerve continuously from the cortex to the periphery and can effectively evoke responses reflecting the brainstem function.

Laryngoscope. 1999 Mar;109(3):492-7.

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Conditioning effect on the long latency potentials in the lower limb to transcranial magnetic stimulation.

Chen JT, Chen CC, Kao KP, Wu ZA, Liao KK.

Neurology, The Neurological Institute, Veterans General Hospital-Taipei, Taiwan.

OBJECTIVES: We used an electrical conditioning stimulation followed by transcranial magnetic stimulation (TMS) to facilitate the occurrence of long latency potentials (LLPs) in order to study the relationship between primary motor evoked potentials (MEPs) and LLPs in the lower limbs.

MATERIALS AND METHODS: The study group included 6 healthy subjects, 1 patient with right thalamic infarction, and 3 patients with spinal cord injuries. The subjects were subjected to electrical conditioning (C) stimulation delivered to the left big toe at 250 Hz in a train of pulses of 20 ms duration prior to TMS (T) from 0 to 150 ms at an increment of 10 ms. The surface electromyographic signals were recorded at the tibialis anterior and gastrocnemius medialis for 400 ms.

RESULTS: The C-T test facilitated both primary MEPs and LLPs with a pattern similar to the primary MEPs of its antagonist. There was no facilitation of the primary MEPs or LLPs in the affected limb of patients with thalamic or spinal cord lesions.

CONCLUSION: At appropriate C-T interval, LLPs could be consistently provoked by TMS. The LLPs were absent in the patients with thalamic infarction and spinal cord injuries. It suggests that LLPs might be provoked through a supraspinal control.

Acta Neurol Scand. 1998 Dec;98(6):412-21.

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Applications of cortical magnetic stimulation.

Maertens de Noordhout A.

Laboratoire de neurophysiologie clinique, hopital de la Citadelle, Liege, Belgique.

In the last decade, a new electrophysiological tool has become available since the development of painless magnetic stimulators able to activate the primary motor cortex and the motor roots in conscious man. Therefore, it became possible to measure the conduction time within fast-conducting central motor pathways by substracting from the total latency of muscle responses elicited by cortical stimuli the conduction time in peripheral nerves. This technique proved sensitive enough to illustrate early abnormalities of central motor conduction in various neurological diseases such as multiple sclerosis, amyotrophic lateral sclerosis, cervical spondylotic myelopathy, degenerative ataxias or hereditary spastic paraplegias. When recorded early after stroke, motor evoked potentials are also a valuable tool to predict functional outcome. They can also illustrate subtle pathophysiological disturbances in diseases where there is no direct involvement of central motor pathways such as Parkinson's disease, dystonia or epilepsy. Magnetic cortical stimulation also offers unique opportunities to explore intracerebral inhibitory and excitatory circuits and mechanisms of brain plasticity. The recent development of rapid rate stimulators also enables functional studies of non-motor cerebral regions such as visual or frontal cortices. Moreover, rapid rate stimulation seems useful in the treatment of drug-resistant depression but the safety of this procedure, particularly with regard to the production of seizures or kindling, remains to be fully documented.

Neurophysiol Clin. 1998 Feb;28(1):9-30.

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Transcranial magnetic stimulation in diagnosis of trigeminal neuralgia.

Kotterba S, Tegenthoff M, Malin JP.

Neurologische Klinik und Poliklinik der Ruhr-Universitat Bochum.

Patients with trigeminal neuralgia are usually investigated by elicitation of the orbicularis oculi reflex and trigeminal evoked potentials. These neurophysiological methods do not allow direct judgement of the trigeminal nerve. By transcranial magnetic stimulation, however, non-invasive investigation of the efferent part of the trigeminal nerve is possible. 10 patients (4 men, 6 women, aged from 43 to 73 years) with trigeminal neuralgia affecting the second or third division were examined. In all patients bilateral long-latency responses after stimulation of the tractus corticonuclearis and short-latency responses after stimulation of the proximal part of the trigeminal nerve were registered. 8 patients showed normal short- and long-latency responses, while in one other patient the long-latency responses were delayed on both sides. The remaining patient revealed a significant difference of amplitude compared to the contralateral long-latency response. This patient had a pontine lesion as shown by blink reflex and a pathological trigeminal evoked potential. In both these latter patients multiple sclerosis was diagnosed. Use of transcranial magnetic stimulation may thus prove helpful in the differential diagnosis of neurological disorders presenting with trigeminal neuralgia.

Nervenarzt. 1994 Apr;65(4):267-70.

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Magnetic brain stimulation: a tool to explore the action of the motor cortex on single human spinal motoneurones.

Mills KR.

University Dept of Clinical Neurology, Radcliffe Infirmary, Oxford, UK.

The human brain can be stimulated by a single intense magnetic pulse over the scalp. Currents induced within the cranium excite the motor cortex and cause limb muscles to contract. The discharge of single motor units, the firing of which is maintained by voluntary effort, can be modulated by magnetic stimuli. Peri-stimulus time histograms suggest that after a cortical stimulus spinal motoneurones are induced to fire by a sequence of EPSPs arising from a train of impulses transmitted monosynaptically over fast-conducting corticospinal fibres. In multiple sclerosis both dispersion of this descending volley and partial transmission failure can impair motoneurone excitation and may explain motor symptoms in these patients.

Trends Neurosci. 1991 Sep;14(9):401-5.

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Magnetic stimulation of the human brain and peripheral nervous system: an introduction and the results of an initial clinical evaluation.

Barker AT, Freeston IL, Jalinous R, Jarratt JA.

This report describes a novel method of stimulating the motor cortex and deep peripheral nerves in humans. The technique, developed in the Department of Medical Physics of Sheffield University, uses a large pulse of magnetic field to induce currents within the body and is painless. The basic principles of magnetic stimulation are described, and the technique is compared with conventional electrical stimulation. Safety aspects are discussed with reference to established clinical electrical and magnetic procedures. The results of the first clinical study using magnetic stimulation are described and show clear central motor pathway slowing in multiple sclerosis patients.

Neurosurgery. 1987 Jan;20(1):100-9.

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