Auditory Neuropathy — Neural and Synaptic Mechanisms

Discussion in 'Research News' started by Juan, Jun 16, 2020.

    1. Juan

      Juan Member

      Tinnitus Since:
      Cause of Tinnitus:
      Several causes
      Auditory neuropathy — neural and synaptic mechanisms

      Key Points
      • Auditory neuropathy impairs speech comprehension severely, beyond the extent that would be expected on the basis of increased threshold of audibility

      • Auditory neuropathy encompasses a range of disease mechanisms that typically disrupt the synaptic encoding and/or neural transmission of auditory information in the cochlea and auditory nerve

      • Auditory synaptopathy, impaired sound encoding at the synapses between inner hair cells and spiral ganglion neurons, results from genetic defects or insults such as exposure to loud noise

      • Advanced physiological and psychophysical testing combined with molecular genetic analysis facilitate diagnostics of auditory synaptopathy and neuropathy

      • Although traditional hearing aids often do not provide substantial benefit for patients with auditory synaptopathy or neuropathy, cochlear implants can provide effective hearing rehabilitation depending on the site(s) of disorder
      Sensorineural hearing impairment is the most common form of hearing loss, and encompasses pathologies of the cochlea and the auditory nerve. Hearing impairment caused by abnormal neural encoding of sound stimuli despite preservation of sensory transduction and amplification by outer hair cells is known as 'auditory neuropathy'. This term was originally coined for a specific type of hearing impairment affecting speech comprehension beyond changes in audibility: patients with this condition report that they “can hear but cannot understand”. This type of hearing impairment can be caused by damage to the sensory inner hair cells (IHCs), IHC ribbon synapses or spiral ganglion neurons. Human genetic and physiological studies, as well as research on animal models, have recently shown that disrupted IHC ribbon synapse function — resulting from genetic alterations that affect presynaptic glutamate loading of synaptic vesicles, Ca2+ influx, or synaptic vesicle exocytosis — leads to hearing impairment termed 'auditory synaptopathy'. Moreover, animal studies have demonstrated that sound overexposure causes excitotoxic loss of IHC ribbon synapses. This mechanism probably contributes to hearing disorders caused by noise exposure or age-related hearing loss. This Review provides an update on recently elucidated sensory, synaptic and neural mechanisms of hearing impairment, their corresponding clinical findings, and discusses current rehabilitation strategies as well as future therapies.
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