Title: A New Method to Screen for Cochlear and Auditory Neural Hearing Impairment
Legend: Leveraging the feedforward and feedback neural networks from the ear to the auditory brainstem, we have developed a novel technique that can concurrently index the function of the sensory cells in the inner ear and the auditory nerve. A schematic of the anatomy of this circuit and technique is shown in Panel A. A brief acoustic stimulus, click, is used to evoke both an acoustic response, otoacoustic emission (OAE), from the sensory cells of the inner ear as well as activate brainstem auditory reflexes, the medial olivocochlear (MOCR) and the middle ear muscle (MEMR) reflex. The average (n = 13) physiological effect of the brainstem auditory reflexes on OAEs is shown in Panel B. The curves are two-term exponential line-fits to the change in OAE across a range of frequencies over 2 seconds when the stimulus is on — the physiological signature of the two reflexes. Notice the OAEs recover to baseline after stimulus cessation (indicated by the black bar). The presence of (1) OAEs indicates the health of the sensory cells, and (2) the characteristic change in the OAE indicates auditory nerve health. The magnitude of OAE change across a range of frequencies for bilateral, right, and left ear stimulations are plotted in Panel C. This plot demonstrates that the bilateral (both ear) stimulation produces the largest effect, ideal for minimizing test time.
Citation: Boothalingam, S., Goodman, S.S., MacCrae, H., and Dhar, S. (under review). A Time-course-based Estimation of the Human Medial Olivocochlear Reflex Function using Clicks. Frontiers in Neuroscience.
Abstract: Hearing impairment (HI) is an epidemic affecting over 1.5 billion individuals of all ages. Globally, unaddressed HI causes losses of ~US$1 trillion each year. Addressing HI requires early detection which current hearing screening tools are inadept at doing efficiently. Specifically, current hearing screening tools can either only index the sensory cells in the inner ear or require measurement of brainstem electroencephalography (EEG) to index the sensory cells and the auditory nerve which require additional resources. To limit the proliferation of HI of all ages, from newborns to adults, we aim to transform hearing screening by translating an innovative and efficient test to the clinic. Specifically, we leverage the feedforward and feedback neural networks from the ear to the auditory brainstem, to concurrently index the sensory cells in the inner ear and the auditory nerve. We use echoes generated by the inner ear called otoacoustic emissions (OAEs) to determine the health of the sensory cells and the physiological effects of the brainstem auditory reflexes, the medial olivocochlear (MOCR) and the middle ear muscle (MEMR) reflex, on OAEs to determine auditory neural health. In this proof-of-concept study, we demonstrate the working of our approach in 13 young normal-hearing individuals. Our results indicate that bilateral stimulation using clicks can successfully both evoke and monitor inner ear and auditory nerve health. Further research in individuals with mild-to-moderate hearing impairment will aid in the clinical translation of our approach.
About the Lab: Sriram Boothalingam’s lab, the Efferent Systems Lab, investigates how the brain controls the functioning of the ear and explores the implications of this control for human hearing. He uses otoacoustic emissions (sounds emanating from the ear), electroencephalography (electrical activity of the brain), and behavioral methods to study the ear-brain-behavior link. His research lies at the intersection of clinical and basic understanding of this link for hearing in children, adults, and individuals exposed to loud sounds.