Impediment of basilar membrane motion reduces overload
protection but not threshold sensitivity: evidence from clinical and experimental
hydrops
Martin Braun
Hear Res 1996, Aug, 97:1-2, 1-10
Abstract
The mechanical function of the basilar membrane (BM) in the mammalian
cochlea has been newly debated after the discovery of frequency selectivity
of single hair cells. Decisive information on this matter can be expected
from hydropic ears, since hydrops presumably alters cochlear mechanics
by (1) impeding BM motion and (2) uncoupling outer hair cell (OHC) stereocilia
from the tectorial membrane (TM). Therefore hearing in Menière's
disease (MD) was examined analysing data on epidemiology of MD types and
audiogram types, 2f thresholds, over-recruitment, loudness intolerance,
and otoacoustic emissions. Further, hearing in experimental hydrops (XH)
was examined analysing data on: morphological changes on TM and OHCs in
relation to hydrops duration; morphological and electrophysiological changes
upon acoustic overstimulation. The results were unequivocal on two points:
(1) co-occurrence of hydrops and normal hearing thresholds can appear
both in MD and XH, (2) co-occurrence of non-hearing-loss hydrops and loudness
hypersensitivity is typical both in MD and XH. The conclusion is that
BM motion apparently is no necessary element in the chain of cochlear
sound transmission but obviously is an auxiliary element for overload
protection through resonant absorption. The results are further indicative
of audiometric methods for an early detection of incipient MD.
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