Dipolar extracellular potentials generated by axonal projections

Abstract

Extracellular field potentials (EFPs) are an important source of information in neuroscience, but their physiological basis is in many cases still a matter of debate. Axonal sources are typically discounted in modeling and data analysis because their contributions are assumed to be negligible. Here, we established experimentally and theoretically that contributions of axons to EFPs can be significant. Modeling action potentials propagating along axons, we showed that EFPs were prominent in the presence of terminal zones where axons branch and terminate in close succession, as found in many brain regions. Our models predicted a dipolar far field and a polarity reversal at the center of the terminal zone. We confirmed these predictions using EFPs from the barn owl auditory brainstem where we recorded in nucleus laminaris using a multielectrode array. These results demonstrate that axonal terminal zones can produce EFPs with considerable amplitude and spatial reach.

Neural Maps of Interaural Time Difference in the American Alligator: A Stable Feature in Modern Archosaurs

“…Putative generators of the neurophonic are the activity of afferent axons, synaptic activation of laminaris neurons, or action potentials in laminaris neurons. Theoretical and experimental analyses provide strong support for the neurophonic originating as a summed coherent signal from the densely packed afferent axons (Kuokkanen et al, 2010(Kuokkanen et al, , 2013(Kuokkanen et al, , 2018McColgan et al, 2017. Similar neurophonics have been recorded in chickens (Schwarz, 1992), in mammals (Weinberger et al, 1970;Henry, 1997;McLaughlin et al, 2010;Day and Semple, 2011;Goldwyn et al, 2014), and now in alligators, and are hypothesized to originate from synaptic potentials (Schwarz, 1992;McLaughlin et al, 2010;Goldwyn et al, 2014).…”

Ephaptic coupling in white matter fibre bundles modulates axonal transmission delays

“…The experimental design would be highly invasive, since the EPs drop rapidly with distance outside fibre bundles. Animal experiments have already demonstrated the possibility to record EPs within axonal fibre bundles [23,42]. An interesting test bed could also be a delay analysis within stimulation-response paradigms used in epileptic patients to determine the seizure focus [43,44].…”

“…First we computed the EPs generated by action potentials in single axons. We use the line approximation [21][22][23], given that the diameters of axons are several orders of magnitude smaller than the diameter (or the general lateral dimensions) of axonal fibre bundles:…”

“…In an open fibre bundle, the EP is determined by currents entering and leaving an axon. The axial currents around an axon can be inferred from the spatial profile of an action potential [23]:…”

LFPy – multimodal modeling of extracellular neuronal recordings in Python

“…This numerical scheme has been applied to predictions of the local field potential (LFP), that is, the low-frequency part of the extracellular potential Lindén et al, 2010Lindén et al, , 2011Gratiy et al, 2011;Makarova et al, 2011;Schomburg et al, 2012;Łęski et al, 2013;Reimann et al, 2013;Martín-Vázquez et al, 2013Głąbska et al, 2014;Mazzoni et al, 2015;Tomsett et al, 2015;Sinha and Narayanan, 2015;Taxidis et al, 2015;Hagen et al, 2016;Głąbska et al, 2016;Ness et al, 2016Ness et al, , 2018Hagen et al, 2017;McColgan et al, 2017), as well as extracellular spike waveforms which carry more power at high frequencies (Holt and Koch, 1999;Gold et al, 2006Gold et al, , 2007Franke et al, 2010;Schomburg et al, 2012;Thorbergsson et al, 2012;Reimann et al, 2013;Ness et al, 2015;Hagen et al, 2015;Miceli et al, 2017;Cserpán et al, 2017;Luo et al, 2018;Buccino et al, 2018Buccino et al, , 2019.…”