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Cortical Deafness (Plus Other Central Hearing Disorders)
Published in Alexander R. Toftness, Incredible Consequences of Brain Injury, 2023
There are many ways to damage that first part of hearing with the ear bones and the cochlea and the conversion into tiny amounts of electricity which make up the peripheral auditory system (Hain, 2007). But for the purposes of this chapter, we are going to pretend that we've made it past those first remarkable steps and are already on our way into the central auditory system in the brain itself. Damage to the central auditory system may result in a variety of central hearing disorders, beginning with cortical deafness.
Stem Cells and Nanotechnology
Published in Stavros Hatzopoulos, Andrea Ciorba, Mark Krumm, Advances in Audiology and Hearing Science, 2020
The human inner ear is divided into two main parts, the auditory system (the cochlea) and the vestibular system. The cochlea is a bony spiral canal, about 30-mm long and divided into three fluid-filled compartments, the scala tympani, the scala media, and the scala vestibuli. The round window membrane (RWM) and the blood inner ear barrier (BB) are two physical barriers that isolate the cochlea, respectively, from the middle ear and from the circulatory system. The RWM is a three-layer semipermeable membrane, composed of an outer epithelial cell layer, a middle connection layer, and an inner connection layer facing the perilymph of the scala tympani (Banerjee and Parnes, 2004). In humans, the variable thickness of RWM affects the response of patients to DD treatments. In animal models, its thickness is different among species but its composition is similar (Goycoolea and Lundman, 1997).
Canine Audiology
Published in Stavros Hatzopoulos, Andrea Ciorba, Mark Krumm, Advances in Audiology and Hearing Science, 2020
Kristine E. Sonstrom, Peter M. Scheifele
Finally, dogs that are placed in acoustically stressful environments (e.g., kennels) have been shown to have measurable changes in hearing over time (Scheifele et al., 2012). Preliminary evidence further suggests that temporary and permanent threshold shifts secondary to significant sources of noise exposure exist in military dogs (Scheifele, 2014; Sonstrom, 2015). Given the substantial amount of evidence regarding noise-induced hearing loss in many species, it is inevitable that there are comparable effects to the canine auditory system when working under similar situations. In the absence of hearing screening or monitoring programs and hearing protection devices, these effects can certainly impact a dog’s ability to hear. This negatively affects their ability to effectively respond to their handler’s commands, especially in challenging acoustic environments. There is abundant evidence indicating that all levels of hearing loss affect speech recognition in humans, especially in the presence of background noise (Flexer, 1999). The outcome of noise effects on the auditory system has resulted in an emphasis on hearing protection devices in different environments, when and where applicable. The goal is to reduce the risk of damage to the auditory system without reducing situational awareness, though this can be a challenging task. Furthermore, attention should be placed on the development of hearing screening and monitoring programs, especially for working canines.
Sound localisation of low- and high-frequency sounds in cochlear implant users with single-sided deafness
Published in International Journal of Audiology, 2023
J. Seebacher, A. Franke-Trieger, V. Weichbold, O. Galvan, J. Schmutzhard, P. Zorowka, K. Stephan
The reason for the improvement in sound localisation when patients with SSD are given a CI in their deaf ear is not yet fully understood. The acoustic information is delivered to the auditory system via two distinctly different pathways: in one ear via normal (acoustic) hearing and on the other side via direct electrical stimulation of the cochlear nerve. Two different inputs (acoustic and electric signals) have to be combined along the auditory pathway in order to evaluate ITDs and ILDs of incident sound. Coding of these cues relevant for localisation of sounds is not primarily considered in today’s CI coding strategies. Originally, the primary focus of development was to improve speech perception, followed by the sound quality. Typically, signal processing in CI is optimised to encode the envelope of the acoustic signal. Fundamental observations were made by Shannon and colleagues, who found that envelope coding of a few tonotopically arrayed frequency bands was already sufficient for speech recognition in patients with CI (Dillon et al. 2016). Current processing strategies further attempt to encode the low-frequency acoustic fine structure information of sound, which could also be used for localisation issues.
Considering hearing loss as a modifiable risk factor for dementia
Published in Expert Review of Neurotherapeutics, 2022
Katharine K. Brewster, Jennifer A. Deal, Frank R. Lin, Bret R. Rutherford
The ability to hear depends on the precise encoding of sound into a neural signal by the peripheral auditory system followed by decoding of the signal into meaning by the brain. When used in the context of this review and unless stated otherwise, ‘hearing loss’ refers to impairments of the peripheral auditory system (cochlea) that affect the precise peripheral encoding of sound. Audiometry is the most common method used to assess hearing ability, and audiometric measures reflect the sensitivity of the peripheral auditory system to detect pure tones. Importantly, detection of pure tones does not substantively depend on higher-order cortical processing [11], meaning that audiometry can be reliably performed in adults with early dementia [12]. Age-related HL is the most common form of HL observed in adults and reflects progressive, irreversible damage to cells within the cochlea. The cochlea is particularly susceptible to damage over time given that most of the inner ear is post-mitotic (and hence incapable of regeneration), with risk factors for HL being age, race, sex, and noise exposure. Animal models of age-related HL as well as postmortem human temporal bone specimens from older adults demonstrate loss of sensory inner and outer hair cells, damage to the stria vascularis, and loss of cochlear nerve fibers [13]. The end result of accumulated damage to the cochlea (‘sensorineural HL’) is impaired encoding of sound and transmission of an impoverished and degraded auditory signal to the brain [14].
Assessment of auditory processing in children with non-syndromic cleft lip and/or palate
Published in Hearing, Balance and Communication, 2022
Melika Zarei, Zahra Hosseini Dastgerdi, Alireza Momeni, Nayyereh Sadat Nouri
Children with CLP and CP are more prone to middle ear infections due to palate deformities [3]. Defects in the palate increase the likelihood of recurrent and chronic otitis media [3,9]. Hearing loss caused by middle ear infection is often fluctuating and causes inconsistent transmission of auditory information, which has a negative effect on neural connection formation. Evidence suggests that transient hearing loss due to middle ear infection causes significant structural and functional changes in the auditory system and leads to processing disorder, especially in early years of life [10]. Recurrent otitis media disrupts the balance of inputs in both ears and adversely affects binaural and temporal processing [10]. processing disorder might not recover even after treatment of middle ear infection, which might negatively affect development of language skills, learning ability, and academic achievement in children [10]. The children did not have a middle ear infection when the tests were carried out in the present study but more than half of the children (12 children) had a history of middle ear infection and ventilation tubes surgery. Therefore, parents and specialists should be highly sensitive to recurrent otitis media and its potential adverse effects on development of auditory function and the resulting APD in CLP children.