Chapter

Electric Fields and Currents in Biological Tissue

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/9780195050387.003.0004
 Electric Fields and Currents in Biological Tissue

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This chapter continues the physical principles of Chapter 3 in the context of biological tissue. Electrophysiology spans about five orders of magnitude of spatial scale, ranging from the microelectrode recordings of transmembrane potentials to millimeter-scale intracranial recordings to centimeter-scale scalp potentials. The classic membrane diffusion equation (core conductor model) is derived from basic principles without reference to any “equivalent circuit.” Tissue electrical properties at several scales are considered with emphasis on the cortical and skull tissues. A volume (current) microsource function and a millimeter scale (current) source function P(r,t) are defined based on fundamental physical and physiological principles. A low-pass filtering effect on cortical potentials is predicted based on reduced (pyramidal cell) microsource/sink separations in cortex at frequencies of perhaps 50 to 100 Hz. The relationship of P(r,t) to scalp potentials is discussed in the context of a Green's function for the head volume conductor, providing equivalent “electrical distances” between sources and scalp electrodes.

Keywords: tissue current; electrophysiology; core conductor model; dipole moment; microsource; mesosource; Green's function; low pass filter

Chapter.  22908 words.  Illustrated.

Subjects: Neuroscience

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