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Published in Terence R. Anthoney, Neuroanatomy and the Neurologic Exam, 2017
Although many recent authors describe the trapezoid body as if it consists entirely of decussating auditory fibers, there are exceptions. Some authors definitely include associated groups of neuronal cell bodies as part of the trapezoid body. For example, “The trapezoid body consists of intermingled cells and fibers” (CH&L, p. 148) or “The trapezoid body also contains intrinsic nuclei” (FitzG, p. 212). Matzke and Foltz, at least, describe the trapezoid body as if it contains all structures in the area of the decussating auditory fibers—i.e., as if it is a region of the pontine tegmentum rather than a specific set of structures: “The point at which the ventral stria [auditory] and medial lemniscus intermingle is called the trapezoid body” (1983, p. 58). Such a definition allows the trapezoid body to include nonauditory structures, such as the medial lemniscus. In their descriptions of the trapezoid body, several recent authors show internal inconsistencies. For example, Barr and Kiernan state that “these fibers [decussating, from the ventral cochlear nucleus], together with others contributed by the superior olivary nucleus, constitute the trapezoid body” (1983, p. 318); yet in Fig. 21–6 on the next page, the trapezoid body is shown to include decussating fibers from the dorsal cochlear nucleus as well. As another example, Afifi and Bergman define the trapezoid body as equivalent to the ventral acoustic stria (1986, p. 147); yet in Fig. 6–6 on the preceding page, the trapezoid body is shown to include fibers arising in the superior olive and nucleus of the trapezoid body as well. As a final example, Williams and Warwick state that “the most ventral contingent of efferent fibres [from the cochlear nuclei] are also the most numerous, forming by their decussation the trapezoid body” (1980, p. 909); yet two pages later, they also include fibers “from the nuclei of the corpus trapezoideum”in the trapezoid body.
Peripheral and central auditory function in adults with epilepsy and treated with carbamazepine
Published in Hearing, Balance and Communication, 2019
Sherifa A. Hamed, Amira M. Oseily
It is well known that anatomical and functional integrity of the peripheral and central auditory pathway are important for normal hearing. In the last three decades, there is an increasing interest in assessment and monitoring of hearing impairment from any cause using BAEPs [27,28,30,33,41]. BAEPs have proven to be more sensitive in detecting subclinical hearing impairment than PTA. BAEPs (short- and middle-latencies) reflect auditory pathway function starting from the auditory nerve and throughout the brainstem [42]. Results of short and middle BAEPs are interpreted as absolute wave latencies (I–V) and interpeak latencies. Waves I originates from afferent activity of the dendrites of the acoustic nerve fibres (first-order neurons) as they leave the cochlea and enter the internal auditory canal. Wave III shows the activity in superior olivary complex which is intimately related to the trapezoid body. Wave V is associated with the lateral lemniscus, the location is the rostral brainstem in or near the inferior colliculus. The I–III, III–V and I–V interpeak latencies (IPLs) reflect brainstem conduction time [42], while long-latency evoked response (also known as event-related potentials [ERPs]) reflects the function within the auditory cortex [43].
Objective evaluation of binaural summation through acoustic reflex measures
Published in International Journal of Audiology, 2018
Vishakha W. Rawool, Madaline Parrill
Binaural summation occurs in the auditory system due to convergence of neural impulses generated by sounds presented to the two ears, primarily at the level of the superior olivary complex (SOC). The SOC includes a collection of brainstem nuclei that serves several functions including localisation, temporal coding of complex sounds and efferent modulation of the cochlear nucleus and cochlea. The two major nuclei in the SOC are referred to as the medial superior olive (MSO) and lateral superior olive (LSO), with approximately 15,500 neurons in the MSO and 5600 neurons in the LSO in humans (Kulesza 2007). Afferents from the ventral cochlear nucleus (VCN) of the same side project on the lateral aspect of the MSO and the afferents from the contralateral VCN project on the medial side of the MSO. MSO receives both excitatory and inhibitory inputs (reviewed in Grothe et al. 2010). The LSO receives direct excitatory input from the ipsilateral anteroventral cochlear nucleus (AVCN) and indirect, inhibitory input from the contralateral AVCN through the medial nucleus of the trapezoid body (MNTB) ipsilateral to the LSO (reviewed in Phillips 2001). Efferent fibres arriving from the LSO and MSO enter the cochlea to form direct or indirect connections with the sensory hair cells. This olivo-cochlear bundle is activated during binaural stimulation and has an inhibitory influence on the cochlear response. In addition, type II multipolar cells within each cochlear nucleus project inhibitory fibres to the contralateral cochlear nuclei (Cant and Gaston 1982). The various inhibitory influences within the auditory brainstem can lead to less than perfect binaural summation.
The effect of cochlear implant age and duration of intervention on ESRT in children with cochlear implant
Published in Cochlear Implants International, 2023
Yashika Tyagi, Indranil Chatterjee
ESRT, whether determined intra- or post-operatively, is an objective measure that can assist in programming the CI device, particularly in patients with unreliable responses (Andrade et al., 2014). ESRT, as well as other objective methods, are apt to provide valuable information required for the CI speech processor programming, subsequently, the measures of comfort may be too high or too low in children when defining the dynamic range determined from behavioural responses. Like the acoustic reflex measured in the diagnostic audiology clinic, the ESRT requires a synchronous response of cochlear nerve neurons to the eliciting stimulus. The afferent response from the stimulated cochlear nerve is sent to the cochlear nucleus in the brainstem and then to the ipsilateral motor nucleus of the facial nerve as well as across the trapezoid body to the superior olivary complex and then to the motor nucleus of the facial nerve on the side contralateral to the ear of stimulation. Next, the efferent stapedial branch of the facial nerve elicits a reflexive contraction of the stapedius muscle in both middle ears. As such, the ESRT is a bilateral response (i.e. the stapedial muscle contracts in both ears in response to stimulation in only one ear). Of pronounced significance, middle ear function needs to be entirely normal for the ESRT to be assessable, because even clinically irrelevant changes in middle ear conduction (i.e. an increase in middle ear stiffness) will inhibit the measurement or additional changes in middle ear stiffness that happen due to the contraction of the stapedius muscle and are basically identified by a time-locked decline in acoustic admittance. ESRT measurements can be done intra-operatively and post-operatively.