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Disorders of Hearing
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
Linda M. Luxon, Ronald Hinchcliffe
Prolongation of the I–III interval can be seen in auditory nerve and cochlear nucleus pathology. Prolongation of the III–V is usually indicated when pathology is sited above the level of the cochlear nucleus, while absent IV and/or V waves are found in cases with involvement of the mid/upper pons. In severe brainstem pathology, waves III–V may be absent. Interaural latency comparisons of wave V are of value in diagnosis of acoustic neurinoma (Figure 19.10c), but may not be useful in detecting brainstem involvement (Weinstein, 1994). In general, while the abnormality in brainstem lesions may be ipsilateral, with respect to the acoustic stimulus, or bilateral, contralateral findings are rare (Musiek and Lee, 1995). The sensitivity and specificity of the auditory brainstem response in identifying brainstem lesions depends on the site of lesion. More caudal intra-axial structured brainstem lesions are identified, but the auditory brainstem response is only moderately sensitive to degenerative disorders or a rostral lesion involving the brainstem. Overall, the sensitivity/specificity of the auditory brainstem response for a variety of brainstem lesions is around 80 per cent, which is less than that noted for acoustic tumours (Musiek and Lee, 1995).
Biomedical Applications of Organic Conducting Polymers
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
Alexander R. Harris, Paul J. Molino, Caiyun Wang, Gordon G. Wallace, Zhilian Yue
Neurotransmitters can be eluted from a conducting polymer to alter cell behaviour. Electrical stimulation of overoxidised PEDOT soaked in GABA, glutamate or aspartate could induce a neural response [122]. 2-amino-5-phosphonopentanoate (AP5) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) have been used as dopants in PPy. These compounds act as inhibitors of NMDA and AMPA-type glutamate receptors. Reduction of PPy ejected the dopant ions and blocked neural activity [123]. An electronic ion pump has also been used to deliver glutamate in the cochlea, leading to a shift in the auditory brainstem response [124].
Optical Cochlear Implants
Published in Francesco S. Pavone, Shy Shoham, Handbook of Neurophotonics, 2020
C. P. Richter, Y. Xu, X. Tan, N. Xia, N. Suematsu
Moser et al. (2013) studied the possibility of using an optogenetic approach for cochlear prostheses. To quantify the ability for stimulating mouse spiral ganglion neurons (SGNs) with blue light, the authors used transgenic mice, which express ChR2 in the somata, dendrites, and axons of SGNs. The blue light was delivered either via the round window or a cochleostomy. Irradiation of the SGNs resulted in a measurable optical auditory brainstem response (oABR) for either of the stimulation configuration (Hernandez et al., 2014).
Hearing loss, lead (Pb) exposure, and noise: a sound approach to ototoxicity exploration
Published in Journal of Toxicology and Environmental Health, Part B, 2018
Krystin Carlson, Richard L. Neitzel
Studies displaying positive results for auditory dysfunction following high doses of Pb predominately used auditory brainstem response (ABR) and analysis of thresholds or waveforms. ABR can be performed in humans and rodents; five main waves are measured as neuronal signals pass from the cochlea to the auditory cortex in the brain. These main waves comprise an afferent pathway traveling sequentially through five major components of auditory processing: Eighth cranial nerve fibers beginning in the cochlea; eighth cranial nerve fiber upon entry to the Cochlear nucleus; action potentials exiting the cochlear nucleus and projecting to the superior Olivary complex; the signal in the Lateral lemniscus; and finally the Inferior colliculus within the midbrain of the brainstem (easily remembered as the underlined text shows ECOLI) (Jewett and Williston 1971; Picton et al. 1974). Following this succession of action potentials, the afferent signal is sent to the medial geniculate within the thalamus and further to the auditory cortex where processing occurs within the temporal lobe (Bartlett 2013). These last processing steps are essential for understanding and recognition of human speech.