Behavioral Evidence for Possible Simultaneous Induction of Hyperacusis and Tinnitus Following Intense Sound Exposure

Abstract

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.

Is noise-induced cochlear neuropathy key to the generation of hyperacusis or tinnitus?

“…Enhanced startle response amplitudes and/or lower startle thresholds, suggestive of hyperacusis, have been reported in animals with hearing loss induced by salicylate (Sun et al 2009), aging (Ison and Allen 2003), or noise (Chen et al 2013). In these studies, startle amplitudes were elevated at all levels above startle threshold.…”

“…The magnitude of tone-or noise-burst PPI can be a useful measure of stimulus detectability (Hoffman and Ison 1980). These startlebased responses are often enhanced after systemic administration of salicylate (Yang et al 2007) and can be enhanced after noise-induced temporary or permanent threshold shift (Chen et al 2013;Sun et al 2012), manipulations known to induce central auditory hyperactivity in animal models (for review, see Kaltenbach 2011 andEggermont 2013). Consequently, these overreactions to sound are interpreted as behavioral signs of hyperacusis.…”

Round and oval window reinforcement for the treatment of hyperacusis

“…Recent animal studies have shown increased hyper-responsiveness and startle behavior induced by noise exposure causing degeneration of the cochlear nerve [18][19][20]. Hyperacusis and tinnitus often occur together, and studies have confirmed the involvement of peripheral neural degeneration in the development of both symptoms [8].…”

Stimulus-timing-dependent modifications of rate-level functions in animals with and without tinnitus

“…While the two pathologies can be easily assessed and distinguished in humans based on direct symptomatology reports and answers to scientifically designed questionnaires, the equivalent evaluations in animal models are challenging. One way of discriminating between the elevated gains due to tinnitus and hyperacusis could be to rely on the assumption that hyperacusis animals should show elevated startle amplitudes and/or elevated normalized prepulse inhibition (Chen et al 2013) across multiple frequencies of the sound stimulation, as hyperacusis is not frequency specific. However, no such pattern could be established in our data.…”