Article

Annals of Biomedical Engineering

, Volume 19, Issue 3, pp 317-328

First online:

A theoretical comparison of electric and magnetic stimulation of the brain

  • Joshua M. SaypolAffiliated withBiomedical Engineering and Instrumentation Program National Center for Research Resources, National Institute of Health
  • , Bradley J. RothAffiliated withBiomedical Engineering and Instrumentation Program National Center for Research Resources, National Institute of Health
  • , Leonardo G. CohenAffiliated withHuman Cortical Physiology Unit Human Motor Control Section Medical Neurology Branch National Institute of Neurological Disorders and Stroke, National Institutes of Health
  • , Mark HallettAffiliated withHuman Cortical Physiology Unit Human Motor Control Section Medical Neurology Branch National Institute of Neurological Disorders and Stroke, National Institutes of Health

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Abstract

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.

Keywords

Magnetic stimulation Electric stimulation Electric field Cortex