Daniel Keller

Gaute T Einevoll

Geir Halnes

Klas H Pettersen

Ole A Andreassen

Tuomo Mäki-Marttunen

BMC Neuroscience

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POSTER PRESENTATION Open Access
Can ionic diffusion have an effect on extracellular
potentials?
Geir Halnes1*, Tuomo Mäki-Marttunen2, Klas H Pettersen3, Daniel Keller4, Ole A Andreassen2, Gaute T Einevoll1,5
From 24th Annual Computational Neuroscience Meeting: CNS*2015
Prague, Czech Republic. 18-23 July 2015
Several pathological conditions, such as hypoxia, anoxia,
ischemia and spreading depression are associated with
ion concentration changes in the extracellular space
(ECS) [1]. Also during non-pathological conditions,
endured periods of intense neural signaling may cause
local ion concentration changes in the millimolar range.
Changes in ion concentrations are often accompanied
by a slow negative potential shift measured in the ECS
[1-3], the origin of which is not properly understood. In
computational neuroscience, it is common to use the
simplifying assumption that diffusive currents (along
concentration gradients) are negligible compared to
Ohmic currents (along electrical fields). This is, for
example, an underlying assumption in the cable equa-
tion used in most multi-compartmental neural models.
It is also an underlying assumption in standard current
source density (CSD) theory, which predicts neural cur-
rent sources from recordings of extracellular potentials.
However, theoretical studies have identified scenarios
where large, but biologically realistic, ion concentration
gradients may induce diffusive currents that are compar-
able in magnitude to Ohmic currents [4,5].
In the current work, we have explored possible effects
that diffusive currents may have on the extracellular
potential in a cortical column. To do this, we developed
a hybrid simulation framework: First, we used the simu-
lator NEURON (and an available multicompartmental
neural model with realistic morphology [6]) to simulate
the transmembrane ionic output from a small popula-
tion of cortical neurons driven by realistic synaptic
input. Next, we used a separate scheme to predict varia-
tions in extracellular potentials and ion concentrations.
The scheme was based on the Nernst-Planck equations
for electrodiffusion and the constraint of electroneutral-
ity, and represents a novel, efficient and generally
applicable method for simulating extracellular dynamics
surrounding multicompartmental neural models or net-
works of such (e.g., the Blue Brain simulator).
Our key findings were: (i) Morphology-dependent dis-
tributions of transmembrane current sources/sinks
induced sustained extracellular potentials. Spatial varia-
tions of the ECS potential were of the order of a few mV
across the depth of the cortical columns, which is similar
to experimentally observed sustained potential profiles
[2,3]. (ii) Long periods of neuronal output (simulations
were run for 80 s) could change local ECS ion concentra-
tions by several millimolars. (iii) For large, but realistic,
concentration gradients in the ECS, diffusive currents
were of the same magnitude as Ohmic currents. (iv) Dif-
fusive currents could have a significant impact on the
sustained extracellular potentials, and could be a possible
explanation to the observed relationship between ionic
shifts and voltage drops in the ECS [1-3]. (v) Variation in
concentrations and diffusive currents took place at the
time scale of several seconds, and had little impact on the
frequencies that are of predominant interest in standard
CSD-analysis.
Authors’ details
1Dept. of Mathematical Sciences and Technology, Norwegian University of
Life Sciences, Ås, Norway. 2NORMENT, Institute of Clinical Medicine,
University of Oslo, Oslo, Norway. 3Centre for Molecular Medicine Norway,
University of Oslo, Oslo, Norway. 4The Blue Brain Project, EPFL, Lausanne,
Switzerland. 5Department of Physics, University of Oslo, Oslo, Norway.
Published: 18 December 2015
References
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* Correspondence: geir.halnes@nmbu.no
1Dept. of Mathematical Sciences and Technology, Norwegian University of
Life Sciences, Ås, Norway
Full list of author information is available at the end of the article
Halnes et al. BMC Neuroscience 2015, 16(Suppl 1):P68
http://www.biomedcentral.com/1471-2202/16/S1/P68
© 2015 Halnes et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://
creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the
original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/
zero/1.0/) applies to the data made available in this article, unless otherwise stated.
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doi:10.1186/1471-2202-16-S1-P68
Cite this article as: Halnes et al.: Can ionic diffusion have an effect on
extracellular potentials? BMC Neuroscience 2015 16(Suppl 1):P68.
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Can ionic diffusion have an effect on extracellular potentials?

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Can ionic diffusion have an effect on extracellular potentials?

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