A new method for spatially selective, non-invasive activation of neurons: concept and computer simulation

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...

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Bibliographic Details
Published in:Medical & biological engineering & computing 2007-01, Vol.45 (1), p.7-24
Main Author: Konings, Maurits K
Format: Article
Language:English
Subjects:
Back Pain - therapy
Biophysical Phenomena
Biophysics
Computer Simulation
Electric Stimulation Therapy - instrumentation
Electric Stimulation Therapy - methods
Electromagnetic Fields
Equipment Design
Humans
Models, Neurological
Neurons
Neurons - physiology
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Summary: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.
ISSN:0140-0118
1741-0444
DOI:10.1007/s11517-006-0136-z