PMID: 8598130Jan 1, 1994Paper

Mechanisms for electrical stimulation of excitable tissue

Critical Reviews in Biomedical Engineering
Bradley J Roth

Abstract

Electric fields excite electrically active tissue by several mechanisms. A long, straight, uniform fiber is polarized by an activating function, proportional to the axial gradient of the axial electric field. During unipolar anodal stimulation, the activating function results in two areas of depolarization (virtual cathodes) that are responsible for anode-make stimulation. During unipolar cathodal stimulation, the virtual anodes can be exploited to produce unidirectional propagation and physiological recruitment of axons. Anode-break stimulation of nerves arises from the intrinsic properties of the sodium channel kinetics; cathode-break stimulation in nerves is anode-break stimulation at a virtual anode. The activating function applies to magnetic stimulation as well as to electric stimulation. Other important mechanisms of stimulation arise if the fiber is terminated, nonuniform, or curved. In the brain, cortical neurons are excited when the electric field is directed from the dendrites toward the axon. Possible mechanisms for cortical excitation are the impedance mismatch between the axon and dendritic tree, and the axon bending as it enters the white matter. Transcranial magnetic stimulation differs from transcranial electri...Continue Reading

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