A Time-Course-Based Estimation of the Human Medial Olivocochlear Reflex Function Using Clicks

Abstract

The auditory efferent system, especially the medial olivocochlear reflex (MOCR), is implicated in both typical auditory processing and in auditory disorders in animal models. Despite the significant strides in both basic and translational research on the MOCR, its clinical applicability remains under-utilized in humans due to the lack of a recommended clinical method. Conventional tests employ broadband noise in one ear while monitoring change in otoacoustic emissions (OAEs) in the other ear to index efferent activity. These methods, (1) can only assay the contralateral MOCR pathway and (2) are unable to extract the kinetics of the reflexes. We have developed a method that re-purposes the same OAE-evoking click-train to also concurrently elicit bilateral MOCR activity. Data from click-train presentations at 80 dB peSPL at 62.5 Hz in 13 young normal-hearing adults demonstrate the feasibility of our method. Mean MOCR magnitude (1.7 dB) and activation time-constant (0.2 s) are consistent with prior MOCR reports. The data also suggest several advantages of this method including, (1) the ability to monitor MEMR, (2) obtain both magnitude and kinetics (time constants) of the MOCR, (3) visual and statistical confirmation of MOCR activation.

The hunt for hidden hearing loss in humans: From preclinical studies to effective interventions

“…Wideband probe stimuli such as chirps or clicks could be used as probe stimuli to overcome this problem and increase sensitivity. Novel MEMR methodologies based on click-evoked otoacoustic emissions such as the one developed by Boothalingam et al (2021) could play an important role in the differential diagnosis of HHL.…”

Auditory Brainstem Mechanisms Likely Compensate for Self-imposed Peripheral Inhibition

“…OAE amplitude was estimated as the RMS of ear canal pressure between 6.5–12.5 ms and the noise floor was estimated by the mean difference of two OAE RMS buffers (even and odd-numbered epochs). Prior to estimating the RMS amplitude, OAEs were considered in the frequency domain to extract OAEs 12 dB above the noise floor to ensure the MOCR-mediated inhibition was estimated only from high quality OAEs (Guinan, 2012; Goodman et al, 2012; Boothalingam et al, 2021). For each duration and rate condition, the RMS of OAE and stimulus amplitude (dB SPL) with noise were subtracted from the RMS without noise to compute the effect of MOCR and MEMR (in dB), respectively.…”

“…When elicited by high level sound, the MEMR stiffens the ossicular chain, altering signal transfer through the middle ear (Boothalingam et al, 2021; Borg, 1968) and may thus confound MOCR effects on OAEs (Boothalingam et al, 2021; Goodman et al, 2013; Guinan et al, 2003). The click stimulus (0–4 ms) in the same frequency range as the OAEs was analyzed to determine the presence of MEMR.…”

“…Ear canal pressures were registered and amplified (+20 dB) by the ER10C+ probe microphone placed in each ear. To avoid changes in stimulus level over the course of the experiment, the probe placement was secured in the ear using foam tips and using silicone putty around the probe in-ear (Silicast, Westone Laboratories, CO; Boothalingam and Goodman, 2021). The MOCR eliciting broadband noise was presented in the contralateral ear using an ER2 (Etymotic Research, IL) insert earphone coupled with a foam tip of appropriate size.…”

“…We predict that if local feedback networks do compensate for the MOCR-mediated peripheral inhibition, a latency between stimulus presentation, peripheral inhibition, and complete compensation would be apparent. Based on the time (~400 ms) it takes for the MOCR inhibition on OHCs to stabilize (Boothalingam et al, 2021; Backus and Guinan, 2006), we speculated that the time taken for complete compensation will fall between 0.5 and a few seconds. To test this prediction, we concurrently measured peripheral (cochlear) and neural (brainstem or cortical) responses in short (1.5 s) and long (4 mins) click-trains.…”