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Neuromodulation, defined by the International Neuromodulation Society as “the alteration of nerve activity through the delivery of electrical stimulation or chemical agents to targeted sites of the body,” is carried out to normalize – or modulate – nerve function. Neuromodulation is an evolving therapy that can involve a range of electromagnetic stimuli such as a strong magnetic field (repetitive transcranial magnetic stimulation), a very small electric current, or a drug instilled directly in the subdural space (intrathecal drug delivery). Emerging applications involve targeted introduction of genes or gene regulators and light (optogenetics), and by 2014, these had been at minimum demonstrated in mammalian models, or first-in-human data had been acquired. The most clinical experience has been with electrical stimulation. Electrical stimulation using implantable devices came into modern usage in the 1980s and its techniques and applications have continued to develop and expand.〔Krames, Elliot S.; Peckham, P. Hunter; Rezai, Ali R., eds. (2009). Neuromodulation, Vol. 1-2. Academic Press. pp. 1–1200. ISBN 9780123742483.〕 The therapy employs the body's natural biological response by stimulating nerve cell activity that can influence populations of nerves by releasing transmitters, such as dopamine, or other chemical messengers such as the peptide Substance P, that can modulate the excitability and firing patterns of neural circuits. There may also be more direct electrophysiological effects on neural membranes as the mechanism of action of electrical interaction with neural elements. The end effect is a “normalization” of a neural network function from its perturbed state. Presumed mechanisms of action for neurostimulation include depolarizing blockade, stochastic normalization of neural firing, axonal blockade, reduction of neural firing keratosis, and suppression of neural network oscillations. Although the exact mechanisms of neurostimulation are not known, the empirical effectiveness has led to considerable application clinically. In general, neuromodulation systems deliver electrical currents and typically consist of the following components: An epidural, subdural or parenchymal electrode placed via minimally invasive needle techniques (so-called percutaneous leads) or an open surgical exposure to the target (surgical “paddle” or "grid" electrodes), or stereotactic implants for the central nervous system, and an implanted pulse generator (IPG). Depending on the distance from the electrode access point an extension cable may also be added into the system. The IPG can have an either a non-rechargeable battery needing replacement every 2–5 years (depending on stimulation parameters) or a rechargeable battery that is replenished via an external inductive charging system. Although most systems operate via delivery of a constant train of stimulation, there is now the advent of so-called “feed-forward” stimulation where the device's activation is contingent on a physiological event, such as an epileptic seizure. In this circumstance, the device is activated and delivers a desynchronizing pulse to the cortical area that is undergoing an epileptic seizure. This concept of feed-forward stimulation will likely become more prevalent as physiological markers of targeted diseases and neural disorders are discovered and verified. The on-demand stimulation may contribute to longer battery life, if sensing and signal-processing demands of the system are sufficiently power-efficient. New electrode designs could yield more efficient and precise stimulation, requiring less current and minimizing unwanted side-stimulation. In addition, to overcome the challenge of preventing lead migration in areas of the body that are subject to motion such as turning and bending, researchers are exploring developing small stimulation systems that are recharged wirelessly rather than through an electrical lead. ==Spinal cord stimulation== (詳細はSpinal cord stimulation is a form of neuromodulation therapy in common use since the 1980s. Its principal use is as a reversible, non-pharmacological therapy for chronic pain management that delivers mild electrical pulses to the spinal cord. In patients who experience pain reduction of 50 percent or more during a temporary trial, a permanent implant may be offered in which, as with a cardiac pacemaker, an implantable pulse generator about the size of a stopwatch is placed under the skin on the trunk. It delivers mild impulses along slender electrical leads leading to small electrical contacts, about the size of a grain of rice, at the area of the spine to be stimulated.〔Bailey, Madeleine. ("A remote control turns off my spine" ), London, UK. The Express. May 14, 2013.〕 Stimulation is typically in the 20–200 Hz range, though a novel class of stimulation parameters are now emerging that employ a 10 kHz stimulation train as well as 500 Hz “burst stimulation”. Kilohertz stimulation trains have been applied to both the spinal cord proper as well as the dorsal root ganglion in humans. All forms of spinal cord stimulation have been shown to have varying degrees of efficacy to address a variety of pharmacoresistant neuropathic or mixed (neuropathic and noiciceptive) pain syndromes such as post-laminectomy syndrome, low back pain, complex regional pain syndrome, peripheral neuropathy, peripheral vascular disease and angina. The general process for spinal cord stimulation involves a temporary trailing of appropriate patients with an external pulse generator attached to epidural electrodes located in the lower thoracic spinal cord. The electrodes are placed either via a minimally invasive needle technique (so-called percutaneous leads) or an open surgical exposure (surgical “paddle” electrodes). Patient selection is key, and candidates should pass rigorous psychological screening as well as a medical workup to assure that their pain syndrome is truly medication-resistant.〔 After recuperating from the implant procedure, the patient will return to have the system turned on and programmed. Depending on the system, the program may elicit a tingling sensation that covers most of the painful area, replacing some of the painful sensations with more of a gentle massaging sensation, although other more recent systems do not create a tingling sensation. The patient is sent home with a handheld remote controller to turn the system off or on or switch between pre-set stimulation parameters, and can follow up to adjust the parameters. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Neuromodulation (medicine)」の詳細全文を読む スポンサード リンク
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