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Published March 1999 | Published + Draft
Journal Article Open

Electrical Interactions via the Extracellular Potential Near Cell Bodies

Abstract

Ephaptic interactions between a neuron and axons or dendrites passing by its cell body can be, in principle, more significant than ephaptic interactions among axons in a fiber tract. Extracellular action potentials outside axons are small in amplitude and spatially spread out, while they are larger in amplitude and much more spatially confined near cell bodies. We estimated the extracellular potentials associated with an action potential in a cortical pyramidal cell using standard one-dimensional cable theory and volume conductor theory. Their spatial and temporal pattern reveal much about the location and timing of currents in the cell, especially in combination with a known morphology, and simple experiments could resolve questions about spike initiation. From the extracellular potential we compute the ephaptically induced polarization in a nearby passive cable. The magnitude of this induced voltage can be several mV, does not spread electrotonically, and depends only weakly on the passive properties of the cable. We discuss their possible functional relevance.

Additional Information

Received March 16, 1998; Revised August 31, 1998; Accepted September 2, 1998. c1999 Kluwer Academic Publishers. We thank David Kewley and James Bower for helpful discussions about electrical potentials and ephaptic interactions and Zachary Mainen and Terrence Sejnowski for making their model of a cortical pyramidal cell available on the web. The research reported here was supported by the Sloan Center for Theoretical Neuroscience at Caltech as well as by the NIMH and NSF.

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