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. 2012;7(9):e45123.
doi: 10.1371/journal.pone.0045123. Epub 2012 Sep 11.

Prepulse inhibition of acoustic startle reflex as a function of the frequency difference between prepulse and background sounds in mice

Sidhesh Basavaraj  1 , Jun Yan
Affiliations

Prepulse inhibition of acoustic startle reflex as a function of the frequency difference between prepulse and background sounds in mice

Sidhesh Basavaraj et al. PLoS One. 2012.

Abstract

Background: Prepulse inhibition (PPI) depicts the effects of a weak sound preceding strong acoustic stimulus on acoustic startle response (ASR). Previous studies suggest that PPI is influenced by physical parameters of prepulse sound such as intensity and preceding time. The present study characterizes the impact of prepulse tone frequency on PPI.

Methods: Seven female C57BL mice were used in the present study. ASR was induced by a 100 dB SPL white noise burst. After assessing the effect of background sounds (white noise and pure tones) on ASR, PPI was tested by using prepulse pure tones with the background tone of either 10 or 18 kHz. The inhibitory effect was assessed by measuring and analyzing the changes in the first peak-to-peak magnitude, root mean square value, duration and latency of the ASR as the function of frequency difference between prepulse and background tones.

Results: Our data showed that ASR magnitude with pure tone background varied with tone frequency and was smaller than that with white noise background. Prepulse tone systematically reduced ASR as the function of the difference in frequency between prepulse and background tone. The 0.5 kHz difference appeared to be a prerequisite for inducing substantial ASR inhibition. The frequency dependence of PPI was similar under either a 10 or 18 kHz background tone.

Conclusion: PPI is sensitive to frequency information of the prepulse sound. However, the critical factor is not tone frequency itself, but the frequency difference between the prepulse and background tones.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. The threshold of auditory brainstem response as a function of tone frequency.
The thresholds were significantly lower in responses to 9 kHz, 13.5 kHz and 20.25 kHz than in responses to 4 kHz, 6 kHz and 30.8 kHz (p<0.001). The difference in the thresholds for 9 kHz and 20.25 kHz tones were statistically insignificant, indicating similar hearing sensitivity between the two frequencies.
Figure 2
Figure 2. ASR with different background sounds.
An example of ASR elicited with a 100 dB SPL white noise burst in the presence of a continuous background tone of 18 kHz at 70 dB SPL (A). Normalized ASR in the presence of no background, white noise, 6 kHz, 10 kHz, 12 kHz, 18 kHz, and 26 kHz (B). ASR was significant smaller for frequency 10 kHz and above than that with white noise background. No significant difference in ASR was demonstrated in the range from 10–26 kHz background frequencies. N: no background sound; S: startle stimulus; W: white noise.
Figure 3
Figure 3. An example of the frequency-dependent prepulse inhibition of the ASR.
The background tone frequency was 18 kHz. The frequency of prepulse tone was from 500 Hz higher to 500 Hz lower than the 18 kHz. The ASR magnitude clearly varied with the frequency difference. The light gray bar at the top represents the continuous background tone. The startle is represented by a darkened area, while the prepulse tone is seen between the arrowhead and the offset of the startle sound. The arrowhead represents the onset of the prepulse tone. Δf: the difference of prepulse frequency from the background frequency.
Figure 4
Figure 4. The percentage changes in ASRP–P, ASRRMS, ASRDUR and ASRLAT as the function of frequency difference (Δf) with a background frequency of 18 kHz.
A significant pattern emerges and is associated with the percentage changes in ASRP–P, ASRRMS, ASRDUR but not for that in ASRLAT, i.e., these values systematically decreased as the function of Δf when the Δf was less than 0.5 kHz. A plateau is clearly evident when Δf was at 0.5 kHz and higher.
Figure 5
Figure 5. The percentage changes in ASRP–P, ASRRMS, ASRDUR and ALAT as the function of frequency difference (Δf) when the background frequency was 10 kHz.
The pattern is similar to those with an 18 kHz background frequency. The gray areas represent the corresponding areas of the standard deviation in Figure 4.
See this image and copyright information in PMC

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