title: A new method for spatially selective, non-invasive activation of neurons: concept and computer simulation.
abstract: Currently available non-invasive neurostimulation devices, using skin electrodes or externally applied magnetic coils, are not capable of producing a local stimulation maximum deep inside a homogeneous conductor, because of a fundamental limitation inherent to the Laplace equation. In this paper, a new neurostimulation method (the DeepFocus method) is presented, which avoids this limitation by using an indirect method of producing electric currents inside tissues: First, cylinder-shaped ferromagnetic rotating disks of non-permanent magnetic material are placed near the skin and magnetized by a non-rotating magnetic coil. Each of the disks rotates at high speed around its own axis of symmetry, thus producing a purely electric Lorentz force field having a non-zero divergence outside the disk, and therefore giving rise to charge accumulations inside the tissues. Subsequently, the magnetic field is switched off suddenly, causing a re-distribution of charge, and hence short-lived electrical currents, which can be used to activate neurons. Two magnet configurations are presented in this paper, and analyzed by computer simulation, showing that the DeepFocus method produces a maximum current density (the 'focus') deep inside the conducting body. The field strength thus created in the focus (7.9 V/m) is strong enough to activate thick myelinated fibers, but can be kept below the threshold for C-fibers, which makes the new method a possible tool for pain mitigation by targeted neurostimulation.
authors.affiliation: Department of Medical Technology, University Medical Center Utrecht, Utrecht, The Netherlands. m.konings@umcutrecht.nl
authors.forename: Maurits K
authors.initials: MK
authors.lastname: Konings
mesh_terms: D001416:Back Pain / Q000628:therapy; D055592:Biophysical Phenomena; D001703:Biophysics; D003198:Computer Simulation; D004599:Electric Stimulation Therapy / Q000295:instrumentation / Q000379:methods*; D004574:Electromagnetic Fields; D004867:Equipment Design; D006801:Humans; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology