Hariprakash Haragopal in his groups lab, where he records electrical responses to sound in Dutch belted rabbits
By Amanda Biederman
Rabbits are known by many for their characteristic long, floppy ears. Yet those ears may hold the secret to understanding hearing loss and, ultimately, creating a more effective hearing aid.
Hariprakash Haragopal is a doctoral student in the Department of Biological Sciences. With his supervisor, Dr. Mitchell Day, Haragopal examines how hearing loss affects sound localization in the brain. Haragopal was awarded second prize in the graduate student competition for his work at Neuroscience Research Day last month.
Normally, sound waves travel as tiny vibrations and reach a snail-shaped organ within the ear, known as the cochlea. There are specialized hair cells within the cochlea, which transduce the mechanical sound vibrations to an electrical signal which is received first by the auditory nerve, and then the brainstem. If the hair cells are damaged, the signal is not properly transmitted and sound perception may be compromised. Haragopal said his research is aimed at better understanding the physiological basis of hearing loss.
“It is known that people with hearing loss have trouble localizing sounds and trying to perceive speech in noise, especially low-frequency noise,” Haragopal said. “We hope that our work on hearing loss and its effects on sound source encoding in the brain will yield some useful results, such as a better hearing aid that can boost certain frequencies and dampen other frequencies.”
Haragopal uses Dutch belted rabbits as a model for hearing loss in humans. This species is ideal for auditory study, Haragopal said, because like humans, these rabbits have the ability to perceive sounds at high and low frequencies. In addition, because Dutch belted rabbits have been studied by many other researchers, there is a plethora of data available on these animals.
Day and Haragopal study the electrical responses to sound in the brains of their hearing-impaired rabbits. Specifically, they quantify a minimum sound level required to generate a measurable electrical response, which they call a threshold. They report that these thresholds are elevated with hearing loss, meaning that higher sound levels are required so the sound can be heard. With these and other results, Haragopal can compare damage and loss of function in both inner and outer hair cells, which are located on different parts of the cochlea.
Thus far, Haragopal has found that the inner and outer hair cells are affected differently during hearing loss. Since the inner and outer hair cells play different roles in sound perception, this finding may help researchers better understand how sound is perceived with hearing loss and, ultimately, design more effective treatments for patients.
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