title: Impedance Spectrum in Cortical Tissue: Implications for Propagation of LFP Signals on the Microscopic Level.
abstract: Brain research investigating electrical activity within neural tissue is producing an increasing amount of physiological data including local field potentials (LFPs) obtained via extracellularin vivoandin vitrorecordings. In order to correctly interpret such electrophysiological data, it is vital to adequately understand the electrical properties of neural tissue itself. An ongoing controversy in the field of neuroscience is whether such frequency-dependent effects bias LFP recordings and affect the proper interpretation of the signal. On macroscopic scales and with large injected currents, previous studies have found various grades of frequency dependence of cortical tissue, ranging from negligible to strong, within the frequency band typically considered relevant for neuroscience (less than a few thousand hertz). Here, we performed a detailed investigation of the frequency dependence of the conductivity within cortical tissue at microscopic distances using small current amplitudes within the typical (neuro)physiological micrometer and sub-nanoampere range. We investigated the propagation of LFPs, induced by extracellular electrical current injections via patch-pipettes, in acute rat brain slice preparations containing the somatosensory cortexin vitrousing multielectrode arrays. Based on our data, we determined the cortical tissue conductivity over a 100-fold increase in signal frequency (5-500 Hz). Our results imply at most very weak frequency-dependent effects within the frequency range of physiological LFPs. Using biophysical modeling, we estimated the impact of different putative impedance spectra. Our results indicate that frequency dependencies of the order measured here and in most other studies have negligible impact on the typical analysis and modeling of LFP signals from extracellular brain recordings.
authors.affiliation: Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre Nijmegen, 6500 HB, Nijmegen, The Netherlands; Department of Neural Networks, Center of Advanced European Studies and Research (caesar), Max Planck Society.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Miceli
authors.affiliation: Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences , 1432 ÅS, Norway.
authors.forename: Torbjørn V
authors.identifier: 0000-0001-9080-8502
authors.initials: TV
authors.lastname: Ness
authors.affiliation: Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, 1432 ÅS, Norway; Department of Physics, University of Oslo, 0316 Oslo, Norway.
authors.forename: Gaute T
authors.identifier: 0000-0002-5425-5012
authors.initials: GT
authors.lastname: Einevoll
authors.affiliation: Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre Nijmegen , 6500 HB, Nijmegen, The Netherlands.
authors.forename: Dirk
authors.identifier: 0000-0002-1202-4363
authors.initials: D
authors.lastname: Schubert
mesh_terms: D000818:Animals; D017097:Electric Impedance; D004558:Electric Stimulation; D005110:Extracellular Space; D008297:Male; D008839:Microelectrodes; D008959:Models, Neurological; D018408:Patch-Clamp Techniques; D017208:Rats, Wistar; D012965:Sodium Chloride; D013003:Somatosensory Cortex / Q000502:physiology*; D046509:Tissue Culture Techniques
chemical_list: D012965:Sodium Chloride
keywords: conductivity; cortex; local field potential; multielectrode array; neuronal tissue; signal frequency 