Biology subjects

Boothalingam, S.

Publications and source records attributed to Boothalingam, S..

4 recordsLinked to original sources

bioRxiv2025

Auditory efferents facilitate intensity change detection in humans: evidence from concurrent ear, brain, and behavior measures

Feedback mechanisms in the brain, such as the medial olivocochlear reflex (MOCR), can aid signal detection and discrimination in noise in animals. Extrapolating these findings in elementary perception to speech understanding in noise abilities in humans has been inconclusive. To investigate the functional role of the MOCR in elementary auditory perception in humans, we concurrently measured ear (otoacoustic emissions) and brain (N1-P2 acoustic change complex [ACC]) responses while participants performed a behavioral intensity change detection task. The intensity change was imposed on a triad of deviant clicks that occurred at early-, middle-, or late-temporal positions of a click train commensurate with null-, partial-, and full activation of the MOCR, respectively. We found faster behavioral detection and shorter ACC latencies for the middle- and late-occurring deviants relative to the early deviant. The improved behavioral detection of later-occurring deviants correlated significantly with the degree of MOCR activation and ACC latency. These mutual correlations suggest a direct involvement of the MOCR in human signal detection, underscored by earlier cortical detection. These novel findings advance our understanding of the mechanisms involved in speech perception in noise and aid in developing hearing assistive technologies.

physiology↗

bioRxiv2022

Auditory Brainstem Mechanisms Likely Compensate for Self-imposed Peripheral Inhibition

It is well known that the medial olivocochlear reflex (MOCR) in the brainstem, part of the efferent network, inhibits the cochlear active gain mechanism. The upstream neural influence of this peripheral inhibition is less understood. When the MOCR is activated, responses generated in the cochlea and cortex undergo putative attenuation, yet the amplitude of responses generated in the brainstem are perplexingly unaffected despite decreased input from the periphery. Based on known neural circuitry, we hypothesized that the inhibition of peripheral input is compensated for by equivalent positive feedback in the brainstem over time. We predicted that the inhibition can be captured at the brainstem with stimuli shorter (1.5 s) than previously employed long durations (4 min) where this inhibition is diminished due to compensation. Results from 18 normal hearing human listeners support our hypothesis in that when the MOCR is activated, there is a robust reduction of responses generated at the periphery, brainstem, and cortex for short stimuli and that brainstem inhibition diminishes for longer stimuli. Our methodology and findings have implications for auditory disorders such as tinnitus, evaluation of efferent function, and provides a novel non-invasive window into potential gain compensation mechanisms in the brainstem.

neuroscience↗

bioRxiv2020

Click evoked Middle Ear Muscle Reflex: Implications for Medial Olivocochlear System Assays

This study describes a time series-based method of middle ear muscle reflex (MEMR) detection using bilateral clicks. Although many methods can detect changes in the OAE evoking stimulus to monitor the MEMR, they do not discriminate between true MEMR-mediated vs. artifactual changes in the stimulus. We measured MEMR in 20 young clinically normal hearing individuals using 1-second-long click trains presented at six levels (65 to 95 dB peak-to-peak SPL in 6 dB steps). Changes in the stimulus levels over the 1 second period were well-approximated by two-term exponential functions. The magnitude of ear canal pressure changes due to MEMR increased monotonically as a function of click level but non-monotonically with frequency when separated into 1/3rd-octave wide bands between 1 and 3.2 kHz. MEMR thresholds estimated using this method were lower than that obtained from a clinical tympanometer in [~]94% of the participants. A time series-based method, along with statistical tests, may provide additional confidence in detecting the MEMR. MEMR effects were smallest at 2 kHz, between 1 and 3.2 kHz, which may provide avenues for minimizing the MEMR influence while measuring other responses (e.g., the medial olivocochlear reflex).

neuroscience↗

bioRxiv2020

Perceptual gating of a brainstem reflex facilitates speech understanding in humans

Navigating "cocktail party" situations by enhancing foreground sounds over irrelevant background information is typically considered from a cortico-centric perspective. However, subcortical circuits, such as the medial olivocochlear (MOC) reflex that modulates inner ear activity itself, have ample opportunity to extract salient features from the auditory scene prior to any cortical processing. To understand the contribution of auditory subcortical nuclei and the cochlea, physiological recordings were made along the auditory pathway while listeners differentiated non(sense)-words and words. Both naturally-spoken and intrinsically-noisy, vocoded speech -- filtering that mimics processing by a cochlear implant--significantly activated the MOC reflex, whereas listening to speech-in-background noise revealed instead engagement of midbrain and cortical resources. An auditory periphery model reproduced these speech degradation-specific effects, providing a rationale for goal-directed gating of the MOC reflex to enhance representation of speech features in the auditory nerve. Our data reveals the co-existence of two strategies in the auditory system that may facilitate speech understanding in situations where the speech signal is either intrinsically degraded or masked by extrinsic auditory information.

neuroscience↗