Modeling local field potentials and their
interaction with the extracellular medium.
Claude Bedard and Alain Destexhe
In: Handbook of Neural Activity Measurement, Edited by
Brette R and Destexhe A, Cambridge University Press, Cambridge,
UK, pp. 136-191, 2012.
In this chapter, we cover the modeling of local field potentials
(LFPs) in neural tissue, with an emphasis on their frequency filtering
properties. The extracellular medium has very complex and
tortuous structure, and its extracellular fluid constitutes only a
few percent of the volume of the tissue. The interaction between
LFPs and this complex extracellular medium gives rise to different
types of frequency filtering properties. Starting from first
principles (Maxwell equations), we first show that the presence of
inhomogeneities of conductivity (such as fluids and membranes) can
give rise to low-pass or high-pass filtering effects. Second, the
extracellular medium contains charged membranes, which will
necessarily react to the electric field by polarization. This
polarization is equivalent to a low-pass filter. Finally, we show
that the ionic diffusion, which is also necessarily associated with
ionic currents, is responsible for another type of filtering.
Diffusion can be responsible for 1/f frequency filtering effects,
which may explain the 1/f frequency scaling of LFPs at low
frequencies. We also introduce a macroscopic model of LFPs which
synthesizes these different effects, and which is consistent with
macroscopic measurements of conductivity in neural tissue.
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