Behavioral evidence for possible simultaneous induction of hyperacusis and tinnitus following intense sound exposure.
Many
human subjects suffering from chronic tinnitus also suffer from
hyperacusis, a heightened perception of loudness at moderate to intense
sound levels.
While numerous studies suggest that animals develop
chronic tinnitus following intense noise exposure, it is not yet clear
whether sound exposure also induces chronic hyperacusis-like responses
in animals.
We addressed this question by examining the chronic effects
of intense sound exposure on the acoustic startle response (ASR) and its
suppression by background noise containing brief gaps.
We compared
startle amplitudes in intense tone-exposed (10 kHz, 115 dB SPL, 4 h) and
age-matched controls at 2-28 weeks post-exposure.
While both groups
showed similar startle thresholds, exposed animals showed a
hyperacusis-like augmentation of ASR at high stimulus levels.
Addition
of background noise had little effect on ASR in controls but had a
strong suppressive effect on startle in exposed animals, indicating a
sensitization to background noise.
When the background noise contained a
gap preceding the startle stimulus, ASR was suppressed in control
animals, but exposed animals showed a marked weakening of gap-induced
suppression of ASR. This weakening of gap-induced startle suppression is
consistent with the interpretation that the gap may have been masked by
tinnitus.
The associated hyper-responsiveness to startle stimuli
presented alone and the sensitization to background noise suggest that
hyperacusis may have also been induced.
The results indicate that noise
exposure leads to increases in the gain of auditory responsiveness and
may offer a model of the association of hyperacusis with tinnitus.
Fuente: Jaro - Journal of the Association for Research in Otolaryngology
2013;Vol 14(3):413 24
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