Near- and far-fields: Source characteristics and the conducting medium in neurophysiology

Dick F. Stegeman, Daniel Dumitru, John C. King, Karin Roeleveld

Research output: Contribution to journalArticle

64 Scopus citations

Abstract

It is possible to appreciate the production of far-field potentials by considering constant current dipolar source voltage distributions in bounded volumes, especially when they are stretched in one direction, e.g., a cylinder. An essentially nondeclining voltage is detected when the recording electrodes are on opposite sides of, and relatively far from, the dipolar source. This voltage maintains its (a) latency, (b) amplitude, (c) morphology, and (d) polarity even if recordings are performed a whole body length away. These four criteria define far-field potentials. A propagating action potential (AP) can be conceptualized as a linear quadrupole or the summation of two dipoles 'back-to-back' (+ - - +). The far-field components of the summated dipoles cancel resulting in the anticipated triphasic waveform for APs with only near-field characteristics, not meeting the first three criteria above. Far-field potentials can be transiently generated when any propagating AP constitutes a net 'real' or 'virtual' dipolar source. 'Real' dipolar sources can occur if an AP encounters the termination of excitable tissue, an alteration in conduction velocity, curvature in excitable tissue resulting in a change in propagation direction, or an abrupt change in resistance of the excitable tissue. Virtual dipolar sources may be produced if an AP encounters a change in the size or shape of the extracellular medium or a transition in extracellular conductivity.

Original languageEnglish (US)
Pages (from-to)429-442
Number of pages14
JournalJournal of Clinical Neurophysiology
Volume14
Issue number5
DOIs
StatePublished - Dec 1 1997

Keywords

  • Bioelectric sources
  • Far-field potentials
  • Modeling
  • Near-field potentials
  • Volume conduction

ASJC Scopus subject areas

  • Physiology
  • Neurology
  • Clinical Neurology
  • Physiology (medical)

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