Date of Award

10-30-2020

Publication Type

Master Thesis

Degree Name

M.Sc.

Department

Biological Sciences

First Advisor

Huiming Zhang

Keywords

auditory midbrain, hearing, inferior colliculus, local-field potentials, neurophysiology, single unit recordings

Rights

info:eu-repo/semantics/openAccess

Abstract

In a natural acoustic environment, our perception to a sound of interest can be affected by an interfering sound. To understand the neural bases of this phenomenon, we used rats to study sound-driven activities in the auditory midbrain, namely the inferior colliculus. As a major central auditory processing center, the inferior colliculus receives a lion’s share of convergent inputs from other auditory structures on both sides of the brain. The neurons of the inferior colliculus are predominantly excited by stimulations to the contralateral ear and inhibited by stimulations to the ipsilateral ear. Integration of these excitatory-inhibitory inputs enable neurons in the structure to compare spatial-temporal information carried by a sound. Based on existing findings, we hypothesized that neural responses in the inferior colliculus to a sound can be suppressed by a preceding sound in a train of stimulus, with the suppressive effect being dependent on the temporal-spatial relationships between the sounds. We recorded local-field potentials from an ensemble of neurons and action potential discharges from individual neurons in the inferior colliculus in response to a pair of leading-trailing tones. The trailing tone was presented at the best frequency of the ensemble of neurons or the individual neuron and was also presented in front of the ear that was contralateral to the site of recording. The leading sound was presented either above or below the best frequency and was either colocalized with the trailing sound or spatially separated from the trailing sound. Results showed that the responses to the trailing tone were suppressed by the leading tone. The suppressive effect was reduced when 1) the leading sound was spatially separated from the trailing sound, and 2) when the two sounds had a large time gap. The effect of spatial separation was evident in neurons that generated transient firing. It is likely that these neurons are important for psychoacoustical phenomena such as spatial release from masking. Results have provided new insights into the neural mechanisms underlying recognition and localization of sounds in a complex acoustic environment.

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