Seminars in Hearing Research at Purdue (SHRP)

Title: Excitatory input characteristics determine temporal coding in auditory thalamus

Speaker: Edward L. Bartlett, Professor, BIO/BME, Purdue University

Authors: Matthew Tharp, Brandon Coventry, Aravindakshan Parthasarathy, and Ed Bartlett

Date: January 21, 2021

Time: 10:30 – 11:20 am

Zoom Info:  contact host

Abstract:

The medial geniculate body (MGB) is the primary sensory input to auditory cortex. As part of a junction between early information from sensory neurons to later cortical and eventual cognitive information, it is suspected that MGB neurons participate in a coding transformation of encoded acoustic stimuli while transmitting stimulus representations through an information processing pathway. During this transformation, neural coding characteristics transition from a time-dependent to a firing rate-dependent format. The ability of individual neurons to preserve information about stimulus features such as frequency or loudness during this transformation is uncertain, and an understanding of underlying transformation mechanisms provides insight for physiologically relevant encoding capabilities. To delineate possible transformation mechanisms, a model of rat MGB firing patterns was constructed in silico using NEURON software. Spike pattern inputs to the MGB model were based upon neural activity evoked by the presentation of various amplitude-modulated sound stimuli. Information theoretic methodology and an analysis of firing rates and vector strengths was utilized to assess various coding characteristics in firing pattern outputs from the model. Parameters were organized to represent physiological properties of either the dorsal (MGd) or ventral (MGv) region of MGB. Results indicate that, depending upon the specifications for inferior colliculus synaptic terminal conditions, the same inputs of auditory information may be represented as one of two distinct coding schemes. The corresponding physiological properties necessary for each coding scheme are found to be representative of actual physiological coding characteristics found within the MGd or the MGv. These results provide evidence for parallel pathways of information transmission within the MGB while suggesting that distinct regions of the MGB participate in divergent representations of the same auditory information through transformation processes dictated by the nature of connections from the inferior colliculus (IC). 

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