About this Research Topic
Multiple sclerosis (MS) is an autoimmune disease of the central nervous system characterized by inflammation, demyelination and neurodegeneration. Throughout the disease course, MS patients can suffer from sensorimotor, cerebellar, emotional and cognitive manifestations. In addition, an accumulation of physical disability occurs with time, but documenting the disease progression remains difficult in the absence of objective sensitive methods.
Transcranial magnetic stimulation (TMS) is a non-invasive technique that continues to attract the attention of scientists and researchers, and might have its place in the evaluation and exploration of symptoms in this clinical population. TMS consists of applying a magnetic field that can activate the corticospinal pathways and generate motor evoked potentials in the corresponding muscle. Single and double pulse paradigms have been applied. While adapting single pulses enables the assessment of the excitability of neuronal membrane and the integrity of the pyramidal tract, using double pulse paradigms has opened the way to the exploration of inhibitory (e.g. intracortical and interhemispheric inhibition) and excitatory (e.g., intracortical and interhemispheric facilitation) circuits of the motor cortex. By doing so, TMS enables the comprehension of pathophysiological mechanisms of several MS symptoms, and could also serve as a tool to monitor the disease evolution and/or its response to therapies. Moreover, in the context of MS, TMS has been employed to assess the physiological correlates of several MS-related symptoms, such as fatigue, anxiety, and depression, among others. Especially as the assessment of these symptoms mainly relies on a handful of subjective scales and an objective evaluation, an assessment offered by TMS is highly needed in this context.
The aim of this Research Topic is to shed light on the utility of excitability measures in MS patients. This concerns original research that employed TMS alone or in combination with pharmacological agents (e.g. GABA and glutamate modulators) or other functional techniques (e.g. electroencephalography, neuroimaging). Review articles that analyze the current literature on cortical excitability are welcomed. Case reports that provide new insights on the utility of this technique also fall within the scope of this subject. In addition, this Topic also considers studies that employ other neurophysiological techniques in this context. Furthermore, works that aim to modulate the corticospinal excitability using noninvasive brain stimulation techniques are also of interest. Exploring the brain physiology in MS patients would not only allow a better understanding of the underlying mechanisms of the disease and its specific symptoms, but may also permit the development of objective tools to monitor its clinical evolution and therapeutic responses.
Keywords: Transcranial Magnetic Stimulation (TMS), Cortical Excitability, Intracortical Inhibition, Intracortical Facilitation, Interhemispheric Inhibition
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