![]() ![]() Sensory hair cells in the cochlea convert sound into neural signals conducted along the auditory nerve fibers (ANFs) by two types of spiral ganglion neurons. In most cases, deficits in hearing performance are caused by a disturbed spiking pattern transmitted from the cochlea to the brain’s processing centers. The ear is a vulnerable organ where sophisticated strategies were developed during evolution to transfer sound into neural signals ( Figure 1) with high precision concerning frequency and loudness ( Von Békésy and Wever, 1960 Mark and Rattay, 1990 Humes et al., 2010). One of the critical impacts of hearing loss is a lack of communication skills in the society. Hearing loss or deafness has several impacts on people’s daily life. (5) Threshold currents of a TN and co-stimulation of degenerated ANFs in other frequency regions depend on the electrode position, including its distance to the outer wall, the cochlear turn, and the three-dimensional pathway of the TN.Īccording to World Health Organization (2020), nearly 466 million people worldwide have impairing hearing loss caused by hereditary, aging, disease, and injury. However, in many cases, a spike in a TN is first initiated in the dendrite, and consequently, dendrite degeneration demands an increase in threshold currents. In a few cases, where weak stimuli elicit spikes of a target neuron (TN) in the axon, dendrite diameter reduction has no effect. (4) Contrary to synaptic excitation, CIs cause several spike initiation sites in dendrite, soma region, and axon moreover, fiber excitability reduces with fiber diameter. ![]() (3) Compared with dendrite diameter, variations in myelin thickness have a small impact on spiking performance. Firing probability reduces through the soma passage due to the low intracellular current flow in thin dendrites during spiking. However, this advantage is lost as their conduction velocity decreases proportionally with the diameter and causes increased spike latency and jitter in soma and axon. (2) Postsynaptic currents from IHCs excite such thin dendrites easier and earlier than under control conditions. Main findings: (1) The unimodal distribution of control dendrite diameters becomes multimodal for hearing loss cases a group of thin dendrites with diameters between 0.3 and 1 μm with a peak at 0.5 μm appeared. The excitation properties of electrical potential distribution induced by two CI were analyzed. An accurate three-dimensional human cochlear geometry, along with 30 auditory pathways, mimicked the CI environment. The impact of dendrite diameter and degree of myelination on neural signal transmission was simulated for (1) synaptic excitation via IHCs and (2) stimulation from CI electrodes. ![]() Type I neurons transmit the auditory information as spiking pattern from the inner hair cells (IHCs) to the cochlear nucleus. Four human cochleae were used to quantify hearing levels depending on dendritic changes in diameter and myelination thickness from type I of the auditory nerve fibers (ANFs). 2Laboratory for Inner Ear Biology, Department of Otorhinolaryngology, Medical University of Innsbruck, Innsbruck, Austriaĭue to limitations of human in vivo studies, detailed computational models enable understanding the neural signaling in the degenerated auditory system and cochlear implants (CIs).1Faculty of Mathematics and Geoinformation, Institute for Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria.Amirreza Heshmat 1,2†, Sogand Sajedi 1†, Lejo Johnson Chacko 2, Natalie Fischer 2*, Anneliese Schrott-Fischer 2 and Frank Rattay 1 ![]()
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