Differential activation of nerve fibers with magnetic stimulation in humans.
BACKGROUND
Earlier observations in our lab had indicated that large, time-varying magnetic fields could elicit action potentials that travel in only one direction in at least some of the myelinated axons in peripheral nerves. The objective of this study was to collect quantitative evidence for magnetically induced unidirectional action potentials in peripheral nerves of human subjects. A magnetic coil was maneuvered to a location on the upper arm where physical effects consistent with the creation of unidirectional action potentials were observed. Electromyographic (EMG) and somatosensory evoked potential (SEP) recordings were then made from a total of 20 subjects during stimulation with the magnetic coil.


RESULTS
The relative amplitudes of the EMG and SEP signals changed oppositely when the current direction in the magnetic coil was reversed. This effect was consistent with current direction in the coil relative to the arm for all subjects.


CONCLUSIONS
A differential evocation of motor and sensory fibers was demonstrated and indicates that it may be possible to induce unidirectional action potentials in myelinated peripheral nerve fibers with magnetic stimulation.
Tuday
Eric C
EC
Department of Bioengineering, University of Utah, Salt Lake City, Utah, USA. etuday@bme.jhu.edu
Olree
Kenneth S
KS
Horch
Kenneth W
KW
D000200:Action Potentials / Q000502:physiology; D000344:Afferent Pathways / Q000502:physiology; D004525:Efferent Pathways / Q000502:physiology; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods; D004576:Electromyography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D006801:Humans; D008280:Magnetics / Q000295:instrumentation*; D008465:Mechanoreceptors / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D010525:Peripheral Nerves / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology