Clinical Neuroscience

[TRANSCRANIAL MAGNETIC STIMULATION: PHYSIOLOGY AND APPLICATIONS]

ARÁNYI Zsuzsanna

DECEMBER 10, 2005

Clinical Neuroscience - 2005;58(11-12)

[Transcranial magnetic stimulation (TMS) is a relatively new technique that allows painless activation of cortical motor neurons. In the clinical setting, TMS is primarily used for the investigation of the corticospinal tract in various neurological diseases, being especially useful in the detection of subclinical dysfunction. In addition to the motor cortex, TMS can be applied to examine other structures inaccessible to electrical stimulation, such as the canalicular portion of the facial nerve. In healthy individuals, TMS can be utilized to monitor excitability changes of the motor system in various situations and muscles, providing valuable information to the understanding of the physiology of motor control. Furthermore, TMS can be used to explore interhemispheric connections as well as intracortical inhibitory and excitatory processes both in health and disease. Finally, with the help of TMS cortical maps of the representation areas of muscles can be constructed, giving insight to both short and long-term cortical plasticity and to the reorganisation of the motor cortex following damage to the brain or acquisition of new motor skills]

COMMENTS

0 comments

Further articles in this publication

Clinical Neuroscience

[THE ROLE OF EVOKED POTENTIAL METHODS IN THE NEUROLOGICAL CLINICAL PRACTICE]

KUNDRA Olga

[The author provides an overview on the value of evoked potential (EP) methods (VEP, SEP, BAEP, MEP) in the diagnosis and follow-up of various neurological diseases (multiple sclerosis, cerebrovascular disorders, degenerative diseases, coma, epilepsy, migraine) by reviewing the literature supported by his own clinical experience. While in the past EP was mainly used for establishing the diagnosis, recently, with the expansion of neuroradiology, it has gained a wider use in the assessment of the severity and extent of the pathologic process and especially in longitudinal follow-up. Its role in the diagnostic phase has diminished. In patients with multiple sclerosis the abnormality of the evoked potentials correlate better with the clinical state than with the MRI results. The method is also suitable to monitor the response to therapy. The importance of the EP tests is illustrated by several case demonstrations.]

Clinical Neuroscience

[PSYCHOPHYSIOLOGICAL AND CLINICAL ASPECTS OF THE EEG SYNCHRONIZATION RELATED TO COGNITIVE PROCESSES]

MOLNÁR Márk, CSUHAJ Roland, CSIKÓS Dóra, HAMVAI Csaba, CZIGLER Balázs, BÁLINT Andrea, GAÁL Zsófia Anna

[The authors review the various forms of EEG-synchronization with special emphasis on the characteristics of the induced and enhanced rhythms. The suggested role of the various EEG frequency bands in the cognitive processes is demonstrated by examples from the literature. The relationship between linear and nonlinear electrophysiological complexity and EEG synchronization is analyzed, with a touch on the use of Omega-complexity and synchronization likelihood methods. In the present study the EEG recorded during adding and subtracting tasks was analyzed with the above methods. It was found that during the adding task the theta band increased in the frontal area, which may be related to activation of working memory processes. Mapping the scalp-distribution of synchronization likelihood also confirmed increased synchronization in the frontal area in addition to which increased values were found in the left temporo-parietal area. The analysis of linear and nonlinear EEG synchronization associated with cognitive processing is suitable to explore the task-related and region specific features of these events.]

Clinical Neuroscience

[BASIC NEUROGRAPHY AND ITS DIAGNOSTIC IMPORTANCE]

KISS Gábor

[Nerve conduction studies are fundamental elements of the neurophysiological investigation of neuromuscular diseases. They provide information on peripheral nerve function. Knowledge of the biological and technical basis of the method is essential for the clinician to understand the place of nerve conduction testing in the diagnostic process. A characteristic feature of the nerve fibers is their ability to conduct electrical potentials. This conductivity changes in pathologic circumstances; therefore, the patient's nerve conduction data may be important if a neuromuscular disorder is suspected. The electrical activity spreading along the nerve fibres can be detected with special techniques and instruments. To perform an examination, a stimulator, a high quality amplifier and a computer with various accessories are necessary. The examination is usually carried out by surface stimulation and recording electrodes and requires some cooperation. By supramaximal stimuli all nerve fibers in the peripheral nerve are activated, and their summated activity is recorded bipolarly. For technical reasons the procedures for the motor and the sensory nerve conduction measurements are somewhat different, but their principles are similar. A number of parameters, such as the latency, the amplitude, the area and the shape of the evoked potentials are analyzed. These parameters are influenced by many biological (age, gender, body height, etc.), physical (such as limb temperature) and technical factors. The results are compared with the reference data. Nerve conduction studies may help distinguish between normal and diseased nerve function. The latter has two main categories; axonal lesion and demyelinisation. Axonal lesion is characterized by relatively normal conduction velocity and lower than normal amplitude of the potentials. Demyelinisation is almost the opposite with long latencies, slow conduction velocity and relatively spared potential amplitudes. Nerve conduction studies help differentiate between these two forms. Abnormalities found by nerve conducion measurement may reflect the severity of the disease. Repeated studies are suitable for quantitative follow-up. The anatomical, physiological, pathophysiological and technical details are discussed below. The characteristic neurographic findings of various diseases are also summarized.]

Clinical Neuroscience

[CONGRESS CALENDAR]

Clinical Neuroscience

[EVENT-RELATED EEG AND EVOKED POTENTIAL INVESTIGATIONS IN THE CLINICAL PRA]

RAJNA Péter, HIDASI Zoltán, WALDEMAR Szelenberger

[Considering the limits of the traditional EEG techniques the authors review the main methods and clinical importance of the event-related EEG investigations. According to methods, these can be classified into the spectral analysis of task-related, pre-task and post-task recordings as well as stimuluscontrolled measurements based on evoked potential techniques. The main results of clinical studies on the eventrelated EEG methods are summarized according to chief disease groups (Alzheimer’s disease, epilepsy, schizophrenia, Parkinson's disease, dyslexia, depression). The authors discuss the stimulus-dependent EEG discharges (P300, cognitive potential) in detail. They present the metaanalysis of 224 recent publications on human application of these methods. They analyze the involved scientific areas and the frequency by which these methods were applied in each. Following this, the results of 83 selected clinical studies are summarized. The frequency of the application of the various event-related EEG methods and the tested wave components and other parameters are listed. Finally a summary of the main clinical results is presented again by groups of diseases (schizophrenia, behavioral disorders, traumatic lesions, enuresis nocturna, depression, memory disturbance and dementia, drug effect). Finally, the potential perspectives and the limitations of the event-related EEG methods are briefly discussed.]

All articles in the issue

Related contents

Clinical Neuroscience

Unanswered questions in the transcranial magnetic stimulation treatment of patients with depression

MORVAI Szabolcs, NAGY Attila, KOVÁCS Attila, MÓRÉ Csaba, BERECZ Roland, FRECSKA Ede

According to the WHO fact sheet depression is a common mental disorder affecting 350 million people of all ages worldwide. Transcranial Magnetic Stimulation (TMS) is a technique which allows the investigator to stimulate and study cortical functions in healthy subjects and patients suffering from various mental and neurological disorders. In the early 1990s, studies revealed that it is possible to evoke long term mood changes in healthy volunteers by rapid rate repetitive, TMS (rTMS) over the frontal cortex. Subsequent studies involving depressed patients found frontal cortical rTMS administered daily to be clinically effective. In the past two decades, numerous trials examined the therapeutic potential of rTMS application in the treatment of mood disorders with constantly evolving treatment protocols. The aim of this paper is to review the literature of the past two decades, focusing on trials addressing the efficacy and safety of rTMS in depressed patients. Our primary goal is to evaluate the results in order to direct future studies which may help investigators in the development of treatment protocols suitable in hospital settings. The time is not far when TMS devices will be used routinely by practitioners primarily for therapeutic purpose rather than clinical research. To our knowledge, a widely accepted “gold standard" that would offer the highest efficacy, with the best tolerability has not been established yet. In order to approach this goal, the most important factors to be addressed by further studies are: localization, frequency, intensity, concurrent medication, maintenance treatments, number of pulses, trains, unilateral, or bilateral mode of application.

Clinical Neuroscience

[The value of motor evoked potentials in the diagnosis of spondylotic myelopathy]

SIMÓ Magdolna, ARÁNYI Zsuzsanna

[Introduction - Motor evoked potential (MEP) is the only method that is able to assess the function of the corticospinal tract in various neurological conditions, such as myelopathies. Myelopathy associated with cervical spondylosis, especially at an early stage, has often slight and non-specific clinical signs, pointing to the importance of the electrophysiological assessment of the spinal cord. The authors' aim was to investigate the sensitivity of MEP examination in the detection of myelopathy secondary to cervical spondylosis. Patients and methods - Patients were classified into three groups according to clinical signs and symptoms: Group I includes patients who have cervical spondylosis as demonstrated by MRI (narrowing of the spinal canal, discal herniation, spinal cord compression) but no complaints or signs suggestive of myelopathy. Results - In Group II patients had minor, non-specific complaints, such as paraesthesia of the legs and gait disturbance raising the possibility of myelopathy, but neurological examination revealed no pyramidal signs. In Group III patients had pyramidal signs as well. In Group I corticospinal function was normal in all patients, as assessed by MEP examination. In Group II all patients had prolonged central motor conduction time or absent responses to cortical stimulation. Likewise, in Group III MEP revealed abnormal corticospinal function in all patients but one. Conclusions - In summary, MEP proved sensitive in the detection of corticospinal dysfunction in myelopathy associated with cervical spondylosis at a stage when clinical signs of pyramidal lesion are not yet present and patients have only minor complaints. On the other hand, if patients are completely symptom free with regard to myelopathy, MEP is also unlikely to disclose corticospinal dysfunction. If pyramidal lesion is evident already by clinical examination, MEP provides no further help. ’Falsenegative’ results are also possible.]

Clinical Neuroscience

[Non-invasive brain stimulation for relieving acute and chronic pain]

CSIFCSÁK Gábor, ANTAL Andrea

[Controlling pain has always been one of the biggest challenges of medical science. Despite pharmacological developments, still many patients suffer from long-lasting pain. During the last 40 years several surgical interventions have been used to modulate the activity of the central nervous system in order to control chronic, pharmacoresistant pain. Because such interventions may involve very serious adverse events, safer and at least equally efficient methods are still required. In the 90’s new techniques of non-invasive brain stimulation have been introduced that enable the facilitation or inhibition of distinct cortical areas. These methods are based on the electrical stimulation of brain structures and to date they have been successfully used to modulate perceptual, cognitive and motor functions in healthy subjects and various diseases as well. In this review we describe such techniques of non-invasive brain stimulation, namely repeated transcranial magnetic stimulation and transcranial direct current stimulation and review the current literature about their efficacy in controlling acute and chronic pain.]

Clinical Neuroscience

[The role of transcranial magnetic stimulation in clinical diagnosis: motor evoked potential (MEP)]

ARÁNYI Zsuzsanna, SIMÓ Magdolna

[Transcranial magnetic stimulation allows painless, non-invasive stimulation, neurophysiological evaluation of nervous structure covered by bone or difficult to access for other reasons. In the clinical setting the technique is mainly used for the investigation of the corticospinal tract (motor evoked potential: MEP). Based upon our experience with patients examined over the course of four years, we have attempted to highlight the clinical situations, where diagnostic help is provided by this technique. MEP in general has proved to be a sensitive and reliable examination. Its significance is apparent mainly in situations where clinical signs of corticospinal tract dysfunction are not evident, or they are masked by lower motoneurone involvement, and where neuroimaging techniques are not informative. The demonstration of subclinical corticospinal lesion is often essential to establish the diagnosis in multiple sclerosis and amyotrophic lateral sclerosis. The technique however received little attention so far with respect to its role in the diagnosis of various spinal cord disorders, and in the demonstration of intact corticospinal function in case of weakness, psychogenic in origin. We have endeavoured to provide further evidence in support of this, and thereby advocating a wider clinical application of the technique.]

Clinical Neuroscience

[Mechanism of the “dark” axonal degeneration in the central nervous system]

PÁL József, GALLYAS Ferenc

[Background and purpose - In the central nervous tissue, two types of transsection-resulted axonal degeneration are generally accepted: “watery” and “dark”. The present paper deals with the assumption that the mechanism of this kind of “dark” axonal degeneration has a relationship with that of the “dark” neuronal degeneration. Methods - A minute stab wound is inflicted in the parietal cortex of the rat brain. From 1 h to 3 months postinjury, the resulted ultrastructural events in two distant regions of the corticospinal tract (internal capsule and C3 region of the corticospinal tract) are studied. Results - As a novel finding, the first morphological process of “dark” axonal degeneration was found to consists in a striking reduction of the distances between neighboring neurofilaments, which were readily distinguishable and apparently undamaged. This pattern (compacted ultrastructure) persisted for hours. By day 1 postinjury, the compacted axoplasmic elements aggregated into a homogenous and dense (“dark”) mass in which hardly any ultrastructural elements could be distinguished. Surrounded by apparently normal or mildly abnormal myelin sheat, this mass underwent a non-isotropic shrinkage during the next three months. Morphological signs of phagocytosis were insignificant. Conclusion - The ultrastructural events during the first day post-injury suggest a non-enzymatic mechanism as an alternative to the prevailing molecular-biological mechanism.]