Title: One Stone, Two Birds: Using Clicks to Monitor Cochlear and Efferent Function
Legend: We have developed a novel approach to investigating the auditory efferent system (ES) using otoacoustic emissions (OAEs), sounds generated by healthy inner ears. (Panel A) Conventional OAE-based methods are limited to testing only roughly 1/4th of the ES as they require additional ES activators. Clicks, short duration sounds, are commonly used to evoke OAEs to study the inner ear but are cautioned against use in the investigations of the ES as the clicks themselves trigger unintended ES activity. (Panel B) We used this caveat to our advantage by titrating the rate and level of click presentation to simultaneously study the inner ear and the ES. The advantage of this method is that it allows for testing the entire ES (i.e., both ears) while also providing the kinetics; neither is possible in conventional methods. Panel C shows the set-up of alternating fast/high and slow/low click stimulation used in our approach. Panel D shows the corresponding rise and fall (kinetics) of ES activity and its magnitude (n=9). Ongoing research is aimed at establishing the test-retest reliability, sensitivity to damage in the auditory system, and robustness to attentional influence of our approach.
Citation: Boothalingam, S., MacCrae, H. and Dhar, S. (2018). Towards the Development of a Test of Auditory Efferents. OAE Evoke: Evoking the Future, Los Angeles, USA. February 2018.
Abstract: The auditory efferent system (ES) originates in the auditory cortex and terminates in the cochlea (inner ear). The activity of the ES has several hypothesized implications for human hearing: facilitating speech understanding in noisy environments, protecting the sensitive inner ear against loud noise, and serving as biological markers of damage in the auditory system. However, a consensus for any of these claims is yet to be established in humans. One reason for this lack of consensus is that the methods used to study the ES using OAEs (1) are not adequately consistent across retests, (2) are possibly affected by attentional state, and (3) only test roughly 1/4th of the ES network. Our novel approach overcomes these limitations by using OAE evoking stimuli to also elicit ES activity, allowing us to simultaneously estimate cochlear and ES function. The implications of our method extend to both clinical (e.g., newborn hearing screening) and basic understanding of the functioning of the ES.
About the Lab: Sriram Boothalingam’s lab investigates how the brain controls the functioning of the ear and explores the implications of this control for human hearing. We use otoacoustic emissions and electroencephalography to study the brain and the ear. Our research lies at the intersection of clinical and basic understanding of this brain control of the ear.