Difference between revisions of "Electrical and Magnetic Stimulation of the Central and Peripheral Nervous System:Modeling of Generated Fields and Data Interpretation"

Magnetic stimulation of the central and peripheral nervous system can now be considered a common method in clinical neurophysiology for assessing the conduction status of motor efferent pathways and peripheral nerves. Introduced in the mid-1980s as an improvement over direct electrical stimulation, it is based on the application of rapidly changing and high-intensity magnetic fields (up to 2 T), which induce an electric field in brain and nerve tissues through electromagnetic induction .  

Regarding existing devices, the focusing capacity provided by the double coil (BF) seems entirely insufficient for using the technique in deep nerve structures, such as the trigeminal nerve roots in gnathology.  A configuration capable of achieving, under certain conditions, volume focusing is the one proposed by Edrich and Zhang.  It consists of two mutually orthogonal coils that can produce the desired focusing effect within tissues, provided that the radii and currents are appropriately selected. By exploiting the mutual surface cancellation effect of the fields induced by each coil, relative maxima can be achieved at depth, along particular directions. Specifically, along the vertical axis passing through the point where the two coils meet, the field induced by the horizontal coil cancels out the field generated by the vertical coil on the surface. In this way, the induced field achieves an internal maximum at a depth of about 3 cm from the surface of the head. This maximum is due to the different spatial distribution, within the sphere, of the field induced by the horizontal coil and that induced by the vertical coil, which combine to produce the surface cancellation effect and volume focusing.

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