Transcranial magnetic stimulation


Posted on Feb 7, 2014

Magnetic stimulation is a non-invasive method of stimulating the brain and peripheral nervous system using induced currents. When used to stimulate the brain it is normally referred to as Transcranial Magnetic Stimulation or TMS. The basic principle is shown schematically in figure 1. Figure 1: The basic principle of transcranial magnetic stimulation showing a time-varying


Transcranial magnetic stimulation
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pulse of current in an external coil causing inducing currents in the brain Magnetic stimulation can be used as an alternative to conventional electrical stimulation of nerves in some applications because it has a number of advantages which are discussed later. Applications include deep peripheral nerve stimulation and the non-invasive and painless stimulation of the human brain, both to elicit responses directly and to modify excitability and plasticity. Electrical stimulation of nerves and muscles was first shown by Galvani and Volta in the 1790s and its mechanism is now well understood1. Such stimulation, whereby excitable membranes are depolarised using current injected into the body via surface or implanted electrodes, is today widely used in both diagnosis and therapy. Examples of the former include measuring the speed of conduction of nerve action potentials in health and disease, and of the latter to stimulate muscles whose neural connections have been compromised to produce functionally useful contractions. Typical pulse parameters used to stimulate superficial nerves via surface electrodes are of the order of 20mA for 100 sec, with up to 250 volts needed to drive this current through the relatively high electrical resistance of the skin. Whilst very effective in many applications, electrical stimulation has some disadvantages. It can sometimes be painful, it is difficult to stimulate deep structures...




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