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arXiv · 0908.3268

Evidence for frequency-dependent extracellular impedance from the transfer function between extracellular and intracellular potentials

Claude Bedard·Serafim Rodrigues·Noah Roy·Diego Contreras·Alain Destexhe
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Abstract

We examine the properties of the transfer function F_T = V_m / V_{LFP} between the intracellular membrane potential (V_m) and the local field potential (V_{LFP}) in cerebral cortex. We first show theoretically that, in the subthreshold regime, the frequency dependence of the extracellular medium and that of the membrane potential have a clear incidence on F_T. The calculation of F_T from experiments and the matching with theoretical expressions is possible for desynchronized states where individual current sources can be considered as independent. Using a mean-field approximation, we obtain a method to estimate the impedance of the extracellular medium without injecting currents. We examine the transfer function for bipolar (differential) LFPs and compare to simultaneous recordings of V_m and V_{LFP} during desynchronized states in rat barrel cortex in vivo. The experimentally derived F_T matches the one derived theoretically, only if one assumes that the impedance of the extracellular medium is frequency-dependent, and varies as 1/sqrt(omega) (Warburg impedance) for frequencies between 3 and 500 Hz. This constitutes indirect evidence that the extracellular medium is non-resistive, which has many possible consequences for modeling LFPs.

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Claude Bedard, Serafim Rodrigues, Noah Roy, Diego Contreras, Alain Destexhe. 2010-05-17. Evidence for frequency-dependent extracellular impedance from the transfer function between extracellular and intracellular potentials. https://arxiv.org/abs/0908.3268

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