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At least 235 records · Page 13Linked to original sources
PubMed1995

Nonlinear effects of noise on phase-locked cochlear-nerve responses to sinusoidal stimuli.

It is well known that, in a cochlear afferent axon with background spike activity, a sinusoidal stimulus (tone) of sufficiently low frequency will produce periodic modulation of the instantaneous spike rate, the alternating half cycles of which comprise excursions above and below the mean background spike rate. It also is known that if the amplitude of the stimulus is sufficiently small, the instantaneous spike rate follows very nearly a sinusoidal trajectory through these positive and negative excursions. For such cases, we define the AC responsiveness of a primary auditory afferent axon to be the amplitude of sinusoidal modulation of the instantaneous spike rate divided by the amplitude of the tone producing that modulation. In the experiments described in this paper, changes in AC responsiveness were followed during and after sudden changes in the background noise level. When the amplitude of the tone was sufficiently small relative to that of the noise, we found that the AC responsiveness can be strongly dependent on the time elapsed since the last change in noise level, while being nearly independent of the amplitude of the tone itself. Under those circumstances, after transitions between noise levels 20 dB apart, we observed changes in AC responsiveness that consistently followed time courses similar to those of the short-term mean (background) spike rate (approximating the adapting response to the noise alone), unfolding over several milliseconds or tens of milliseconds. At the time of the transition between noise levels, there was another change in AC responsiveness, which appeared to be instantaneous; as the noise level increased, the AC responsiveness immediately increased with it. This seemingly paradoxical effect and the similarity of the time courses of AC responsiveness and short-term mean spike rate both are consistent with a simple, descriptive model of spike generation involving the shifting of threshold along a bell curve.

Acoustic Stimulation↗
PubMed2001

Cerebro-oculo-facio-skeletal syndrome as a human example for accelerated cochlear nerve degeneration.

BACKGROUND: Cerebro-oculo-facio-skeletal (COFS) syndrome is a rare autosomal-recessive disorder that includes microcephaly, severe mental retardation, and multiple congenital anomalies. Otologic findings are usually limited to descriptions of the auricles. PATIENT AND METHODS: The authors report inner ear histopathologic findings of a deceased 13-year-old patient with COFS. A histologic study of the inner ear in COFS syndrome has not yet been described. This patient was documented as having a profound bilateral sensorineural hearing loss at the age of 2 years. RESULTS: Histologic evaluation revealed accelerated neural and neuronal degeneration at the cochlear and retrocochlear levels. Remaining myelinated nerve fibers, counted in the spiral lamina, had degenerated by up to 97% when compared with normal innervation densities. Afferent nerve fibers innervating inner hair cells were completely absent, whereas medial efferent fibers to outer hair cells were found. Vestibular nerve fibers were less affected. CONCLUSION: The authors report inner ear findings that differ from animal models of primary cochlear neural degeneration and that resemble the pattern of hereditary cochlear nerve degeneration reported in Friedreich's ataxia.

Abnormalities, Multiple↗
PubMed2004

Relationship between cochlear implant outcome and the diameter of the cochlear nerve depicted on MRI.

This study aimed to evaluate the relationship between the diameters of the auditory and eighth cranial nerves and improvements in post-implant performance. Twenty prelingually deafened children (aged from 2.0 to 6.0 years) who received the Nucleus 24 cochlear implant participated in this study. All subjects had used their implant for at least 1 year after device connection. The diameters of cochlear and eighth cranial nerves were retrospectively measured on preoperative T2-weighted axial magnetic resonance image (MRI). In 17 of 20 subjects, the cochlear and eighth cranial nerves could be identified on MRI. The mean diameter of the cochlear and eighth cranial nerves were 0.9 +/- 0.2 mm and 1.2 +/- 0.3 mm, respectively. In the remaining three subjects, the cochlear and eighth cranial nerves could not be identified on MRI. These three subjects had significantly lower scores in the Infant-Toddler-Meaningful Auditory Integration Scale (IT-MAIS) than the other 17 subjects at 12 months post-implant. There was no significant correlation among the maximal diameters of the nerves and age, ECAP thresholds and IT-MAIS scores. A sufficient outcome from cochlear implantation can be expected when cochlear and eighth cranial nerves are depicted on MRI, regardless of the nerve diameters.

Analysis of Variance↗