Contribution to the former "hair cell list" from Jan 30, 2002

On October 16, 2001, Ian Russell wrote:

"In the mustached bat cochlea and mouse, the lengths of OHCs remain constant
for frequency regions above about 20 kHz, so there is no correlation between
OHC length and frequency tuning, and I do not now think that the mechanical
resonance that we elicited has anything to do with tuning in the cochlea. I
cannot remember measuring a resonance above about 3 kHz ......"

We now have direct evidence that in the mustached bat frequency selectivity
is effected by tuned OHCs at least up to 61 kHz, and probably up to 100 kHz.

In a combined behavioral, physiological and anatomical study Kössl and Vater
extensively documented the total dependence of frequency selectivity on OHC
function:

Kössl, M. and Vater, M. (2000). "Consequences of Outer Hair Cell Damage for
Otoacoustic Emissions and Audio-vocal Feedback in the Mustached Bat," JARO
1, 300-314.

1) Moderate OHC lesions by the antibiotic Amikacin reduced threshold
sensitivity, but left the strong OAEs in the auditory fovea at ca. 61 kHz
intact. These OAEs were reduced in frequency by a few hundred Hz, which was
the same amount by which hearing and echolocation calls of the bats
were shifted as well.

2) Strong OHC lesions by the antibiotic Amikacin dramatically reduced
threshold sensitivity and finally abolished the strong OAEs at ca. 61 kHz.
After the disappearance of these OAEs the bats lost all frequency
selectivity in their auditory fovea. This became evident, because the
animals completely lost the frequency control of their echolocation calls.

In conclusion:
This paper elegantly documents a condition in which IHCs, BM, and TM are
fully intact, but all frequency selectivity in the animal's main hearing
range is lost due to OHC lesions. This condition proves that tuned OHCs are
a necessary element for frequency selectivity, even in the high-frequency
hearing of bats.

Martin

--------------------------------------------
Martin Braun
Neuroscience of Music
S-671 95 Klässbol
Sweden
web site: http://w1.570.telia.com/~u57011259/index.htm

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