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Induction of enhanced acoustic startle response by noise exposure: dependence on exposure conditions and testing parameters and possible relevance to hyperacusis.

Salloum RH, Yurosko C, Santiago L, Sandridge SA, Kaltenbach JA - PLoS ONE (2014)

Bottom Line: In an effort to gain insight into these discrepancies, we conducted measures of acoustic startle responses (ASR) in animals exposed to different levels of sound, and repeated such measures on consecutive days using a range of different startle stimuli.Since many studies combine measures of acoustic startle with measures of gap detection, we also tested ASR in two different acoustic contexts, one in which the startle amplitudes were tested in isolation, the other in which startle amplitudes were measured in the context of the gap detection test.The results reveal that the emergence of chronic hyperacusis-like enhancements of startle following noise exposure is highly reproducible but is dependent on the post-exposure thresholds, the time when the measures are performed and the context in which the ASR measures are obtained.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurosciences, The Cleveland Clinic, Cleveland, Ohio, United States of America.

ABSTRACT
There has been a recent surge of interest in the development of animal models of hyperacusis, a condition in which tolerance to sounds of moderate and high intensities is diminished. The reasons for this decreased tolerance are likely multifactorial, but some major factors that contribute to hyperacusis are increased loudness perception and heightened sensitivity and/or responsiveness to sound. Increased sound sensitivity is a symptom that sometimes develops in human subjects after acoustic insult and has recently been demonstrated in animals as evidenced by enhancement of the acoustic startle reflex following acoustic over-exposure. However, different laboratories have obtained conflicting results in this regard, with some studies reporting enhanced startle, others reporting weakened startle, and still others reporting little, if any, change in the amplitude of the acoustic startle reflex following noise exposure. In an effort to gain insight into these discrepancies, we conducted measures of acoustic startle responses (ASR) in animals exposed to different levels of sound, and repeated such measures on consecutive days using a range of different startle stimuli. Since many studies combine measures of acoustic startle with measures of gap detection, we also tested ASR in two different acoustic contexts, one in which the startle amplitudes were tested in isolation, the other in which startle amplitudes were measured in the context of the gap detection test. The results reveal that the emergence of chronic hyperacusis-like enhancements of startle following noise exposure is highly reproducible but is dependent on the post-exposure thresholds, the time when the measures are performed and the context in which the ASR measures are obtained. These findings could explain many of the discrepancies that exist across studies and suggest guidelines for inducing in animals enhancements of the startle reflex that may be related to hyperacusis.

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Stimulus sequences used to test the effect of acoustic context on ASR.Startle stimuli of different intensities (blue blocks) are presented as bursts separated by different time intervals (red double-headed arrows). In the first context (A), silence is maintained during the inter-stimulus interval (black lines) throughout the test battery. In the second context (B), a background noise, with or without an intervening gap of silence, fills some of the inter-stimulus intervals, but the startle stimulus only condition is identical to that in context 1. In either context, numbered solid blue block are those used to determine the ASR. Red diamond: time interval during which the background noise is interrupted by a gap.
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pone-0111747-g001: Stimulus sequences used to test the effect of acoustic context on ASR.Startle stimuli of different intensities (blue blocks) are presented as bursts separated by different time intervals (red double-headed arrows). In the first context (A), silence is maintained during the inter-stimulus interval (black lines) throughout the test battery. In the second context (B), a background noise, with or without an intervening gap of silence, fills some of the inter-stimulus intervals, but the startle stimulus only condition is identical to that in context 1. In either context, numbered solid blue block are those used to determine the ASR. Red diamond: time interval during which the background noise is interrupted by a gap.

Mentions: Because the ASR is known to be sensitive to the presence of background noise [23]–[26], we tested whether ASR amplitudes might differ significantly depending on the context in which the startle stimuli were presented. In this experiment, startle eliciting stimuli were presented in two different ways. In the first method, ASRs were tested using a stimulus battery that included only startle-eliciting noise bursts presented randomly at different levels (Fig. 1A). In the second, ASRs were measured using the same startle-eliciting noise bursts that were used in the first method, except that these stimuli were inserted randomly in a battery of stimuli used to measure gap detection ability; this stimulus battery thus included startle eliciting stimuli preceded by background noise (with or without gaps of silence) as well as startle eliciting noise bursts not preceded by background noise (Fig. 1B). This experiment design allowed us to address the question of whether the startle amplitude evoked by identical stimuli (noise bursts) differs depending on the acoustic context (i.e., the presence or absence of a recent history of background noise in the test battery).


Induction of enhanced acoustic startle response by noise exposure: dependence on exposure conditions and testing parameters and possible relevance to hyperacusis.

Salloum RH, Yurosko C, Santiago L, Sandridge SA, Kaltenbach JA - PLoS ONE (2014)

Stimulus sequences used to test the effect of acoustic context on ASR.Startle stimuli of different intensities (blue blocks) are presented as bursts separated by different time intervals (red double-headed arrows). In the first context (A), silence is maintained during the inter-stimulus interval (black lines) throughout the test battery. In the second context (B), a background noise, with or without an intervening gap of silence, fills some of the inter-stimulus intervals, but the startle stimulus only condition is identical to that in context 1. In either context, numbered solid blue block are those used to determine the ASR. Red diamond: time interval during which the background noise is interrupted by a gap.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4216136&req=5

pone-0111747-g001: Stimulus sequences used to test the effect of acoustic context on ASR.Startle stimuli of different intensities (blue blocks) are presented as bursts separated by different time intervals (red double-headed arrows). In the first context (A), silence is maintained during the inter-stimulus interval (black lines) throughout the test battery. In the second context (B), a background noise, with or without an intervening gap of silence, fills some of the inter-stimulus intervals, but the startle stimulus only condition is identical to that in context 1. In either context, numbered solid blue block are those used to determine the ASR. Red diamond: time interval during which the background noise is interrupted by a gap.
Mentions: Because the ASR is known to be sensitive to the presence of background noise [23]–[26], we tested whether ASR amplitudes might differ significantly depending on the context in which the startle stimuli were presented. In this experiment, startle eliciting stimuli were presented in two different ways. In the first method, ASRs were tested using a stimulus battery that included only startle-eliciting noise bursts presented randomly at different levels (Fig. 1A). In the second, ASRs were measured using the same startle-eliciting noise bursts that were used in the first method, except that these stimuli were inserted randomly in a battery of stimuli used to measure gap detection ability; this stimulus battery thus included startle eliciting stimuli preceded by background noise (with or without gaps of silence) as well as startle eliciting noise bursts not preceded by background noise (Fig. 1B). This experiment design allowed us to address the question of whether the startle amplitude evoked by identical stimuli (noise bursts) differs depending on the acoustic context (i.e., the presence or absence of a recent history of background noise in the test battery).

Bottom Line: In an effort to gain insight into these discrepancies, we conducted measures of acoustic startle responses (ASR) in animals exposed to different levels of sound, and repeated such measures on consecutive days using a range of different startle stimuli.Since many studies combine measures of acoustic startle with measures of gap detection, we also tested ASR in two different acoustic contexts, one in which the startle amplitudes were tested in isolation, the other in which startle amplitudes were measured in the context of the gap detection test.The results reveal that the emergence of chronic hyperacusis-like enhancements of startle following noise exposure is highly reproducible but is dependent on the post-exposure thresholds, the time when the measures are performed and the context in which the ASR measures are obtained.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurosciences, The Cleveland Clinic, Cleveland, Ohio, United States of America.

ABSTRACT
There has been a recent surge of interest in the development of animal models of hyperacusis, a condition in which tolerance to sounds of moderate and high intensities is diminished. The reasons for this decreased tolerance are likely multifactorial, but some major factors that contribute to hyperacusis are increased loudness perception and heightened sensitivity and/or responsiveness to sound. Increased sound sensitivity is a symptom that sometimes develops in human subjects after acoustic insult and has recently been demonstrated in animals as evidenced by enhancement of the acoustic startle reflex following acoustic over-exposure. However, different laboratories have obtained conflicting results in this regard, with some studies reporting enhanced startle, others reporting weakened startle, and still others reporting little, if any, change in the amplitude of the acoustic startle reflex following noise exposure. In an effort to gain insight into these discrepancies, we conducted measures of acoustic startle responses (ASR) in animals exposed to different levels of sound, and repeated such measures on consecutive days using a range of different startle stimuli. Since many studies combine measures of acoustic startle with measures of gap detection, we also tested ASR in two different acoustic contexts, one in which the startle amplitudes were tested in isolation, the other in which startle amplitudes were measured in the context of the gap detection test. The results reveal that the emergence of chronic hyperacusis-like enhancements of startle following noise exposure is highly reproducible but is dependent on the post-exposure thresholds, the time when the measures are performed and the context in which the ASR measures are obtained. These findings could explain many of the discrepancies that exist across studies and suggest guidelines for inducing in animals enhancements of the startle reflex that may be related to hyperacusis.

Show MeSH
Related in: MedlinePlus