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Auditory Efferent System
Published in Stavros Hatzopoulos, Andrea Ciorba, Mark Krumm, Advances in Audiology and Hearing Science, 2020
Thalita Ubiali, Maria Francisca Colella-Santos
The SOC is involved in the final pathway whereby the cortex, and subcortical nuclei along the auditory pathway, can connect with the cochlea, comprising the olivocochlear system. This system has ipsi and contralateral projections to the inner ear: the lateral olivocochlear (LOC) and the medial olivocochlear (MOC) bundles, both originated in the lateral and medial regions of the SOC, respectively. LOC projections are thin and mainly ipsilateral with unmyelinated fibers that make synapses with the auditory nerve dendrites located beneath the IHC. MOC bundle, differently, is predominantly contralateral, with thicker and myelinated axons that project toward the body of the OHC in the contralateral cochlea (Guinan, 2006). Figure 3.1 shows a simplified illustration of the olivocochlear system connections.
Cochlear mechanisms and processes
Published in Stanley A. Gelfand, Hearing, 2017
The central nervous system influences the active processes of the cochlea via the efferent innervation of the OHCs from the medial efferent (olivocochlear) system (e.g., Guinan, 1996, 2006; Robles and Ruggero, 2001; see also Chapters 2 and 6). Among other effects, activation of the medial efferent system has been found to, for example, reduce the magnitude and nonlinearity of basilar membrane vibrations in the vicinity of the characteristic frequency (e.g., Murugasu and Russell, 1996; Dolan et al., 1997; Russell and Murugasu, 1997; see also Chapter 6).
Physiology of Hearing
Published in James R. Tysome, Rahul G. Kanegaonkar, Hearing, 2015
The olivocochlear system supplies descending fibres from the superior olive to the cochlea. It is divided into two: the lateral and medial systems. The lateral system has its cell bodies in or around the lateral superior olive (depending on the species) and the medial system has its cell bodies medial to the lateral superior olive, in the periolivary region of the superior olive. The lateral system terminates on the dendrites of the auditory nerve fibres, whereas the medial system directly contacts the OHCs. The role of the lateral olivocochlear efferent system is not known. There are three main hypotheses concerning the role of the medial olivocochlear efferent system: (1) protection from loud sounds; (2) improving detection of sounds in noise; and controlling cochlear mechanics.
Vestibular suppression of normal bodily sounds
Published in Acta Oto-Laryngologica, 2020
Neil S. Longridge, Anielle Lim, Arthur Ian Mallinson, Jim Renshaw
The olivocochlear bundle (OCB) is a poorly understood efferent pathway which serves to protect the inner ear. It originates in the superior olivary complex and projects to both the ipsilateral and contralateral cochlea [5,6]. The lateral olivocochlear system (LOCS) has uncrossed synapses on type 1 spiral ganglion cells projecting to the inner hair cells (IHCs) [4,5]. On the other hand, the medial system (MOCS) innervates the outer hair cells (OHCs) and the majority of their fibers project to the contralateral cochlea [5,6]. Once the efferent reflex is activated, the medial system can hyperpolarize OHCs, decrease the gain of the cochlear amplifier, decrease sensitivity of the IHCs, and also, reduce the responses of the auditory nerve fibers [6].
Sensory profiles, behavioral problems, and auditory findings in children with autism spectrum disorder
Published in International Journal of Developmental Disabilities, 2023
Ummugulsum Gundogdu, Ahmet Aksoy, Mehtap Eroglu
OAE is an easily administered, objective test that can be performed quickly. OAEs are basically according to the stimulus type; They are divided into stimulated and spontaneous. Evoked OAEs are of three types: stimulus frequency otoacoustic emissions (SFOAE), transient evoked otoacoustic emissions (TEOAE), and distortion product otoacoustic emissions (DPOAE) (Kemp 2002, Lonsbury-Martin and Martin 2003). In a study conducted in Turkey, 40 ears, including the right and left ears of 20 healthy volunteers aged 6–17 with normal hearing, and 40 ears of right and left ears of 20 individuals diagnosed with ASD between the ages of 6–17 with normal hearing were evaluated using DPOAE (Yüksel 2021). In this study, signal-to-noise ratios (SNR) and amplitude values (λ) at 1 kHz.–1.5 kHz.–2 kHz.–3 kHz–4 kHz and 6 kHz were evaluated. DPOAE values of individuals with autism are at SNR values (3-4-6) kHz compared to the control group and amplitude values (4–6) kHz. It was obtained as high. The authors stated that due to the study findings, children with autism might have hyperacusis originating from the inner ear (Yüksel 2021). In other studies, it has been suggested that central auditory pathways and medial olivocochlear system incompatibilities may also cause hyperacusis (Zanchetta and Furtado 2020). In our study, when comparing those who adapted to and passed the OAE test with those who failed the unilateral and bilateral tests, irritability was more common in individuals who failed the OAE test than in those who passed it. The presence of OAE suggests normal cochlear function (Kemp 2002, Shera 2004). Owing to irritability, some children could not adapt to the test and may have remained unilateral or bilateral during the test.
Auditory event-related potentials and function of the medial olivocochlear efferent system in children with auditory processing disorders
Published in International Journal of Audiology, 2019
Thierry Morlet, Kyoko Nagao, L. Ashleigh Greenwood, R. Matthew Cardinale, Rebecca G. Gaffney, Tammy Riegner
Deficits in the top-down peripheral processes, not necessarily exclusive of other deficits in the afferent auditory system and/or cognitive functions including attention, have also been suggested as a potential source of APD. Through the efferent fibres of the medial olivocochlear system (MOCS), the brain regulates the processing of sounds by the auditory periphery. When activated acoustically, the MOCS inhibits the activity of the outer hair cells as shown by a decrease in the level of otoacoustic emissions, with the strongest efferent effect obtained for binaural stimulation, followed by ipsilateral and contralateral stimuli. The inhibitory function of the MOCS can lead to an improvement in coding of signals embedded in noise, suggesting an antimasking role. Furthermore, activation of the MOCS in humans has been shown to improve the detection of tones embedded in ipsilateral noise, speech-in-noise intelligibility in normally hearing adults, and speech-in-noise perception in normal children (Lopez-Poveda 2018, for a review). In these studies, individuals who have better performance in noise tended to demonstrate larger suppression of the otoacoustic emissions than those with lower performance. Other studies however, have shown either a lack of significant correlation (Stuart and Butler 2012; Wagner et al. 2008) or an inverse correlation (de Boer, Thornton, and Krumbholz 2012) between MOCS activity and speech in noise performance. These conflicting results regarding whether or not MOC activity is involved in speech in noise recognition might be explained by a number of reasons, such as differences in testing protocols of evaluating the MOCS activity with OAEs, the speech perception tasks and the signal to noise ratio of the speech material. Despite the still incomplete understanding of the MOCS role in hearing in noise, it is conceivable to hypothesise that an impairment of the MOCS could be associated with an APD since a common feature of APD is the child’s failure to perceive auditory stimuli in the presence of competing speech or background noise. In clinical populations, studies have shown that despite normal hearing thresholds, some children with APD, language impairment, or even dyslexia, exhibit a decrease in the function of the MOCS innervating the outer hair cells (Morlet et al. 2003; Muchnik et al. 2004; Sanches and Carvallo 2006; Veuillet, Collet, and Bazin 1999; Veuillet et al. 2007).