Why and How Does the Brain Control Our Ears? Sriram Boothalingam’s ASHF-funded research investigates the auditory efferent system and how otoacoustic emissions can measure it. Foundational Questions
Foundational Questions  |   October 01, 2018
Why and How Does the Brain Control Our Ears?
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Article Information
Hearing & Speech Perception / Hearing Disorders / ASHA News & Member Stories / Foundational Questions
Foundational Questions   |   October 01, 2018
Why and How Does the Brain Control Our Ears?
The ASHA Leader, October 2018, Vol. 23, online only. doi:10.1044/leader.FQ.23102018.np
The ASHA Leader, October 2018, Vol. 23, online only. doi:10.1044/leader.FQ.23102018.np
Name: Sriram Boothalingam, PhD, assistant professor, Communication Sciences and Disorders, University of Wisconsin–Madison
ASHFoundation awards
  • 2016 ASHA Research Conference Travel Grant

  • 2015 New Investigators Research Grant ($10,000), “Development of a Novel Method to Measure Binaural Efferent Strength”

What is the focus of your research?
Why and how does the brain control our ears? My research program is driven by the need to understand the implications of the top-down brain-ear link, called the auditory efferent system, for human hearing. Through the investigation of basic efferent function, I am also evaluating how this system varies in pathologies, such as cochlear synaptopathy.
A secondary focus is using otoacoustic emissions (OAEs) to build tools to reliably measure the top-down influence of auditory efferents on hearing. OAEs are extra energy generated in a healthy inner ear that emanate to the external ear canal as sound. We use a sensitive microphone placed in the ear canal to measure this tiny sound. I chose OAEs as my primary tool as they are already widely used clinically, including in newborn hearing screening.
How did your award from the ASHFoundation lead to your current work?
The New Investigator award allowed my post-doc mentor, Sumit Dhar, and I to develop a novel test of the auditory efferent function using OAEs. This test overcomes several limitations of current methods. One such limitation is the difficulty in measuring binaural efferent function. This is important because both our ears are controlled by the efferent system. But conventional testing of the auditory efferent system—activating the efferents using noise in one ear while using OAEs to monitor changes inflicted by the efferents on the other ear—allows only for testing the efferent function in one ear.
Our method circumvents the need for a separate noise stimulus in the opposite ear by using a single stimulus (click) to perform both functions. We use clicks to concurrently elicit efferent activity while also capturing that efferent activity using OAEs in the same ear. Because our method requires only one ear to both stimulate the efferent system and monitor its activity, the opposite ear can be used to infer information about binaural efferent function. Our method also allows estimation of the kinetics of the efferents—we can estimate how efferent activity changes over time from the start of the stimulus to the end. This new dimension allows us to see differences in efferent function across people by looking not just at the overall magnitude of the activity, but also at how fast the efferent system kicks in. It is similar to obtaining both the amplitude and the latency of the auditory brainstem response (ABR) peaks.
Several previous investigators have done much of the groundwork on different ways of eliciting the efferents, and such pioneering work guided our approach. My ASHFoundation grant allowed me to test new approaches to activating the efferents and to tinker with various parameters to maximize information obtained efficiently. But much work is needed to make this test of efferents clinically viable. I am applying for further funding to improve the method.
What do you hope to demonstrate through your research—or what has it already demonstrated?
My ultimate goal is to better understand why evolution has still left us with the auditory efferents, what purpose they serve to humans, and how the efferents achieve what they intends to achieve. This is an active area of research, and previous researchers have laid a sound foundation (pun intended) for new investigators to work on.
Considering the variability across people in OAE levels and in efferent activity, and any complex interactions that the two may produce, efferent assays have struggled with test-retest reliability in the past. I hope our new method will aid in understanding the efferents better and more reliably.
Why did you choose this particular research focus?
When I learned that there are reverse connections between the brain and the ear, and that the brain controls the ear, I was completely hooked! We need to understand why and how the efferents work, and I see a lot of untapped diagnostic potential in efferents. My quest to understand the efferents better led me to learn more about OAEs, the most viable non-invasive tool to study the efferents. The fact that OAEs exist—the fact that our ears generate their own sound—is nothing short of a miracle. Eyes cannot make light and other sensory organs can’t make their own senses. Studying these two incredible mechanisms is immensely rewarding.
How has ASHFoundation funding affected your professional life?
ASHFoundation funding kick-started my current research program. It might have even aided me in securing my current position. Apart from funding, the ASHA Lessons for Success was an immensely helpful exercise. I feel very honored to have received ASHF funding, which has truly been a stepping stone for my career.
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October 2018
Volume 23, Issue 10