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Clin Neurophysiol. 2009 Jun;120(6):1183-7. doi: 10.1016/j.clinph.2009.03.023. Epub 2009 May 6.

What does the ratio of injected current to electrode area tell us about current density in the brain during tDCS?

Author information

1
Institute of Biophysics and Biomedical Engineering, Faculty of Science, University of Lisbon, 1749-016 Lisbon, Portugal. pcmiranda@fc.ul.pt

Abstract

OBJECTIVE:

To examine the relationship between the ratio of injected current to electrode area (I/A) and the current density at a fixed target point in the brain under the electrode during transcranial direct current stimulation (tDCS).

METHODS:

Numerical methods were used to calculate the current density distribution in a standard spherical head model as well as in a homogeneous cylindrical conductor.

RESULTS:

The calculations using the cylindrical model showed that, for the same I/A ratio, the current density at a fixed depth under the electrode was lower for the smaller of the two electrodes. Using the spherical model, the current density at a fixed target point in the brain under the electrode was found to be a non-linear function of the I/A ratio. For smaller electrodes, more current than predicted by the I/A ratio was required to achieve a predetermined current density in the brain.

CONCLUSIONS:

A non-linear relationship exists between the injected current, the electrode area and the current density at a fixed target point in the brain, which can be described in terms of a montage-specific I-A curve.

SIGNIFICANCE:

I-A curves calculated using realistic head models or obtained experimentally should be used when adjusting the current for different electrode sizes or when comparing the effect of different current-electrode area combinations.

PMID:
19423386
PMCID:
PMC2758822
DOI:
10.1016/j.clinph.2009.03.023
[Indexed for MEDLINE]
Free PMC Article
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