Effects of Age and Noise Exposure on Proxy Measures of Cochlear Synaptopathy.
Garreth Prendergast, Samuel Couth, Rebecca E Millman and 4 others
PMID 31558119WHAT IT FOUND
In adults with normal hearing, age and estimated lifetime noise exposure did not predict brainstem or envelope-following measures thought to index cochlear synaptopathy.
A speech-in-noise test showed age and noise exposure effects, but noise exposure predicted better high-level performance, not damage.
Key findings
01Age and lifetime noise exposure did not predict the electrophysiological proxy measures: the ABR Wave I/V model had p = .358 and the EFR model had p = .495.
02The DTT speech-in-noise differential was predicted by age (standardized beta .441, p .0001) and noise exposure (standardized beta -.288, p .001), but in opposite directions to the synaptopathy hypothesis.
03When standard-range audiometric thresholds replaced 16-kHz thresholds, the DTT model remained significant with age, noise exposure, and 500-Hz threshold all predicting performance.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study is cross-sectional, so it cannot show that age or noise exposure caused any change. Lifetime noise exposure was estimated from participants' recall, and the paper notes that this subjective approach has limitations. The older group had only 33 participants, so the extended age range may not provide stable estimates. Between-subject variability in young listeners was high, and the paper states that a large sample would be needed to estimate age effects on electrophysiological measures. All participants had clinically normal thresholds, but this still allowed a 30-dB range of hearing within the standard frequency region. The analyses relied on the low-SR synaptopathy hypothesis, which the paper notes may not explain human findings. The significant DTT and AMD models did not support the expected direction for noise-induced synaptopathy. The cohort had normal audiometric thresholds, so it does not show how these measures would perform in patients with hearing loss.
The easy way to misread this
Do not read the significant DTT result as evidence that noise exposure causes cochlear synaptopathy. Higher noise exposure predicted better performance at 80 dB relative to 40 dB, the opposite direction to the synaptopathy hypothesis, and the electrophysiological proxy measures were null.