The Middle Ear Muscle Reflex in Rat: Developing a Biomarker of Auditory Nerve Degeneration.
Mark E Chertoff, Ashley Martz, Joey T Sakumura and 2 others
PMID 29189520WHAT IT FOUND
In rats, a special probe measured the middle ear muscle reflex, and its amplitude, threshold, timing, and decay changed with sound frequency and level.
This is early animal work on a possible auditory nerve biomarker, not a human test.
Key findings
01The measured reflex response disappeared after the animal was sacrificed, so it was not an artifact or signal leakage.
02Reflex amplitude increased with elicitor sound level, and threshold was lowest at 3 kHz compared with 10 kHz and 16 kHz.
03Reflex decay varied with sound level and frequency; at 10 kHz the decay time lengthened from about 1.7 seconds at 50 dBSPL to 10 seconds at 100 dBSPL.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study was done in anesthetized rats, not people, so it does not show how the reflex works in patients. Rat reflex thresholds and likely function differ from humans; the paper notes rat thresholds were much lower than human thresholds. Only 19 rats were studied, and 16 kHz reflexes were not attempted in 2 of them. Reliability was checked in only five animals. Anesthesia may have affected latency and rise time, and the authors say this could explain differences from other rat studies. Opening the bulla may have changed the middle ear frequency response. The methods describe elicitor levels from 100 to 35 dBSPL in 5 dB steps, while the group data report levels from 100 to 50 dBSPL in 10 dB steps. The paper reports normative reflex values and a model, not a tested biomarker for auditory nerve degeneration.
Declared interests
No conflict-of-interest declaration appears in the article text. The article is listed as supported by NIH extramural research.
The easy way to misread this
Do not read this as evidence that middle ear muscle reflex decay can diagnose human auditory nerve degeneration or hidden hearing loss. The data are from anesthetized rats, and the paper states that the best reflex parameter for estimating nerve survival remains to be determined.