Silent Gap Detection Paper

the silent gap would occur. Gaps and other prestartle stimuli (prepulse inhibition) have been previously used in laboratory animals and humans as an audiometric tool to quantify features of the acoustic environment that a subject can detect(Bauer et al., 1999; Li et al., 2013). More salient prestartle stimuli, including gaps, inhibit the startle response to a greater degree than less salient stimuli. When an animal effectively detects a silent gap embedded in the acoustic background, its subsequent response to a startle stimulus is reduced in magnitude. Gap detection, prepulse inhibition (PPI), and auditory brainstem response (ABR) threshold will be tested before and 1 wk (6–7 d) after sham- or noise exposure. Gap detection paradigm will be
The ambient sound in the chamber was 46 dB SPL (4–40 kHz). All sounds are presented through a planar isodynamic tweeter (RT2H-A; HiVi), which is positioned in front of the animal to reduce standing wave resonances. A 50-ms sound gap was introduced 130 ms before the startle stimulus. Startle response represents the time course of the downward force (presented as arbitrary units, AU) that the mouse applies onto the platform in response to the startle stimulus. Gap detection will be evaluated by the gap startle ratio, which is the ratio of the peak-to-peak value of the startle waveform in trials with gap over the peak-to-peak amplitude of the startle waveform in trials in the absence of the gap. Noise-exposed mice that showed an increase in gap startle ratio by more than 0.3 in at least one tested frequency will be considered as tinnitus mice. The hearing thresholds of left ear of sham- and noise-exposed mice will be measured using ABR
To ensure that the mouse is able to detect the gap in the background sound before noise- or sham exposure, gap startle ratio for a single test frequency before exposure is required to be below 0.9. To control for potential prepulse excitation effects, the gap startle ratio after exposure is required to be below 1.1. Frequencies that meet the above requirements are considered as valid frequencies and were used for further analysis. To determine whether a valid frequency is a tinnitus or a nontinnitus frequency, we will measure and analyze the variability of changes in gap detection in sham exposed (control) mice before and 1 wk after sham exposure. The probability distribution of changes in gap startle ratio in control group is fitted with a normal distribution. On the basis of this analysis, we will identify the valid frequency. This frequency was more than 0.3; otherwise this frequency was a nontinnitus frequency. After assessing all six background frequencies in each mouse, we consider the mouse as a tinnitus mouse if it shows at least one tinnitus