Annals of Biomedical Engineering

, Volume 19, Issue 3, pp 317–328

A theoretical comparison of electric and magnetic stimulation of the brain

  • Joshua M. Saypol
  • Bradley J. Roth
  • Leonardo G. Cohen
  • Mark Hallett


We present a theoretical comparison of the electric field produced in the brain by three modalities of transcranial stimulation of the cortex: magnetic stimulation, bifocal electric stimulation, and unifocal electric stimulation. The primary focus of this comparison is the focality and direction of the electric fields produced. A three-sphere model is used to represent the scalp, skull, and brain. All electric fields are calculated numerically. For magnetic stimulation we consider only a figure-of-eight coil. We find that magnetic stimulation produces the most focal field, while unifocal electric produces the least. Fields produced during magnetic stimulation are parallel to the head surface, while fields produced during electric stimulation have components both parallel and perpendicular to the head surface. The electric field produced by magnetic stimulation is shown to be insensitive to the skull conductivity, while that produced by electric stimulation is very sensitive to it.


Magnetic stimulation Electric stimulation Electric field Cortex 


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Copyright information

© Pergamon Press plc 1991

Authors and Affiliations

  • Joshua M. Saypol
    • 1
  • Bradley J. Roth
    • 1
  • Leonardo G. Cohen
    • 2
  • Mark Hallett
    • 2
  1. 1.Biomedical Engineering and Instrumentation Program National Center for Research ResourcesNational Institute of HealthBethesda
  2. 2.Human Cortical Physiology Unit Human Motor Control Section Medical Neurology Branch National Institute of Neurological Disorders and StrokeNational Institutes of HealthBethesda

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