Title: The auditory brainstem reflex tag-team
Legend: The auditory brainstem reflex tag-team: panel A is a schematic of the neural connections between two brainstem auditory reflexes, the medial olivocochlear (MOCR) and the middle ear muscle (MEMR) reflex. While we know that the two reflexes work in tandem and at slightly different frequencies and input sound levels, how the activity of one reflex influences the other is poorly understood. We investigated the influence of the MOCR on the activation threshold of the MEMR in 20 young normal-hearing adults. Data in panel B is the activation threshold (lowest sound level required to activate) of the MEMR as a function of MOCR strength. At input levels where the MOCR is most active (77 to 89 dB ppeSPL), a direct relationship exists between the two reflex activities. That is, because the MOCR activation threshold is lower compared to the MEMR, the MOCR activity likely increases the level at which the MEMR becomes active. It appears that the two reflexes work synergistically as a tag-team to maximize benefit for hearing.
Citation: Boothalingam, S., Goodman, S.S., Broyles, K., and Stans, A. S. (in prep). The auditory brainstem reflex tag-team: interactions between the medial olivocochlear (MOCR) and the middle ear muscle (MEMR) reflex.
Abstract: The auditory efferent system (ES) originates in the auditory cortex and terminates in the inner ear, via the medial olivocochlear reflex (MOCR), and in the middle ear, via the middle ear muscle reflex (MEMR). 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. While we know that the two reflexes work in tandem and at slightly different frequencies and input sound levels, how the activity of one reflex influences the other is poorly understood. We investigated the influence of the MOCR on the activation threshold of the MEMR in 20 young normal-hearing adults. Our results suggest that at stimulus levels where the MOCR is most active (77 to 89 dB ppeSPL), a direct relationship exists between the two reflex activities. That is, because the MOCR activation threshold is lower compared to the MEMR, MOCR activity likely increases the level at which the MEMR becomes active. It thus appears that individuals with stronger MOCR derive greater benefit from the MOCR and individuals with a weaker MOCR derive greater benefit from the MEMR. Together, it appears that the two reflexes work synergistically as a tag-team to maximize benefit for hearing.
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. 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 and adults.