title: A model of the medial superior olive explains spatiotemporal features of local field potentials.
abstract: Local field potentials are important indicators of in vivo neural activity. Sustained, phase-locked, sound-evoked extracellular fields in the mammalian auditory brainstem, known as the auditory neurophonic, reflect the activity of neurons in the medial superior olive (MSO). We develop a biophysically based model of the neurophonic that accounts for features of in vivo extracellular recordings in the cat auditory brainstem. By making plausible idealizations regarding the spatial symmetry of MSO neurons and the temporal synchrony of their afferent inputs, we reduce the challenging problem of computing extracellular potentials in a 3D volume conductor to a one-dimensional problem. We find that postsynaptic currents in bipolar MSO neuron models generate extracellular voltage responses that strikingly resemble in vivo recordings. Simulations reproduce distinctive spatiotemporal features of the in vivo neurophonic response to monaural pure tones: large oscillations (hundreds of microvolts to millivolts), broad spatial reach (millimeter scale), and a dipole-like spatial profile. We also explain how somatic inhibition and the relative timing of bilateral excitation may shape the spatial profile of the neurophonic. We observe in simulations, and find supporting evidence in in vivo data, that coincident excitatory inputs on both dendrites lead to a drastically reduced spatial reach of the neurophonic. This outcome surprises because coincident inputs are thought to evoke maximal firing rates in MSO neurons, and it reconciles previously puzzling evoked potential results in humans and animals. The success of our model, which has no axon or spike-generating sodium currents, suggests that MSO spikes do not contribute appreciably to the neurophonic.
authors.affiliation: Center for Neural Science, New York University, New York, New York 10003, Courant Institute of Mathematical Sciences, New York University, New York, New York 10012, and jgoldwyn@nyu.edu.
authors.forename: Joshua H
authors.identifier: http://orcid.org/0000-0001-5733-9089
authors.initials: JH
authors.lastname: Goldwyn
authors.affiliation: Laboratory of Auditory Neurophysiology, Medical School, Campus Gasthuisberg, University of Leuven, B-3000 Leuven, Belgium.
authors.forename: Myles
authors.initials: M
authors.lastname: Mc Laughlin
authors.affiliation: Laboratory of Auditory Neurophysiology, Medical School, Campus Gasthuisberg, University of Leuven, B-3000 Leuven, Belgium.
authors.forename: Eric
authors.initials: E
authors.lastname: Verschooten
authors.affiliation: Laboratory of Auditory Neurophysiology, Medical School, Campus Gasthuisberg, University of Leuven, B-3000 Leuven, Belgium.
authors.forename: Philip X
authors.identifier: http://orcid.org/0000-0002-9759-5375
authors.initials: PX
authors.lastname: Joris
authors.affiliation: Center for Neural Science, New York University, New York, New York 10003, Courant Institute of Mathematical Sciences, New York University, New York, New York 10012, and.
authors.forename: John
authors.initials: J
authors.lastname: Rinzel
mesh_terms: D000818:Animals; D001306:Auditory Pathways / Q000502:physiology; D002415:Cats; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D005260:Female; D008297:Male; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology*; D009847:Olivary Nucleus / Q000502:physiology*
keywords: auditory brainstem; computer model; local field potential; medial superior olive; neurophonic