| Popis: |
Noise-induced cochlear synaptopathy, the loss of the synaptic connections between inner hair cells and afferent auditory nerve fibers, has been demonstrated in multiple animal models, including non-human primates. However, given that synaptopathy can only be confirmed with post-mortem temporal bone analysis, it has been difficult to determine whether noise-induced synaptopathy occurs in humans. Human studies of noise-induced synaptopathy using physiological indicators identified in animal models (auditory brainstem response [ABR] wave I amplitude, the envelope following response [EFR], and the middle ear muscle reflex [MEMR]) have yielded mixed findings. Differences in the population studied may have contributed to the differing results. For example, due to differences in the intensity level of the noise exposure, noise-induced synaptopathy may be easier to detect in a military Veteran population than in populations with recreational noise exposure. We previously demonstrated a reduction in ABR wave I amplitude and EFR magnitude for young Veterans with normal audiograms reporting high levels of noise exposure compared to non-Veteran controls. In this report, we expand on the previous analysis in the same population to determine if MEMR magnitude is similarly reduced. The results of the statistical analysis, although not conventionally statistically significant, suggest a reduction in mean MEMR magnitude for Veterans reporting high noise exposure compared with non-Veteran controls. In addition, the MEMR appears relatively insensitive to subclinical outer hair cell dysfunction and is not well correlated with ABR and EFR measurements. When combined with our previous ABR and EFR findings in the same population, these results suggest that noise-induced synaptopathy occurs in humans. In addition, the findings indicate that the MEMR may be a good candidate for non-invasive diagnosis of cochlear synaptopathy/deafferentation and that the MEMR may reflect the integrity of different neural populations than the ABR and EFR. |
