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.

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Abstract

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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