Chapter

Current Sources in a Homogeneous and Isotropic Medium

Paul L. Nunez and Ramesh Srinivasan

in Electric Fields of the Brain

Second edition

Published in print January 2006 | ISBN: 9780195050387
Published online May 2009 | e-ISBN: 9780199865673 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780195050387.003.0005
 Current Sources in a Homogeneous and Isotropic Medium

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This chapter demonstrates the relationship of current sources to recorded potentials in volume conductors using a simple salt water fish tank experiment consisting of a dipole current source and separate measuring circuit. In such a conductive medium, the behavior of potentials is determined only by the geometric arrangement of current sources and sinks. Examples include the monopole, the dipole, and various distributed source-sink systems, including the action potential source distribution and “closed field” examples. These idealized source configurations are related to Rall's well known branched dendrite models of extracellular field potentials. Theoretical source models are shown to agree approximately with genuine potentials recorded in a cat brain (superior olive) and near an isolated, active frog sciatic nerve. Actual experimental potentials represent space-averages over the volume of the electrode tip. Recorded dynamics can be scale-sensitive or fractal-like; the dynamic behavior recorded at one scale need not match that of other scales.

Keywords: monopole; dipole; dipole layer; action potential sources; closed field; dendrite sources; sciatic nerve

Chapter.  16017 words.  Illustrated.

Subjects: Neuroscience

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