Center for Neural Science
New York University
April 8, 2014
A model of the medial superior olive explains spatio-temporal features of local field potentials
Local field potentials are valued probes 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 three-dimensional volume conductor to a one-dimensional problem. We find that post-synaptic currents in bipolar MSO neuron models generate extracellular voltage fields that strikingly resemble in vivo recordings. Simulations reproduce distinctive spatio-temporal features of the in vivo neurophonic response to monaural pure tones: large oscillations (hundreds of microvolts to millivolt scale), 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 since coincident inputs are thought to evoke maximal firing rates in MSO neurons.
This work is in collaboration with John Rinzel (NYU), Philip Joris (University of Leuven, Belgium), Myles Mc Laughlin (University of Leuven, Belgium), and Eric Verschooten (University of Leuven, Belgium).