Modification of the rat's startle reaction by an antecedent change in the acoustic environment

Auditory Behavior in Adult-Blinded Mice

Cross-modal plasticity occurs when the function of remaining senses is enhanced following deprivation or loss of a sensory modality. Auditory neural responses are enhanced in the auditory cortex, including increased sensitivity and frequency selectivity, following short-term visual deprivation in adult mice (Petrus et al. Neuron 81:664-673, 2014). Whether or not these visual deprivation-induced neural changes translate into improved auditory perception and performance remains unclear. As an initial investigation of the effects of adult visual deprivation on auditory behaviors, CBA/CaJ mice underwent binocular enucleation at 3-4 weeks old and were tested on a battery of learned behavioral tasks, acoustic startle response (ASR), and prepulse inhibition (PPI) tests beginning at least 2 weeks after the enucleation procedure. Auditory brain stem responses (ABRs) were also measured to screen for potential effects of visual deprivation on non-behavioral hearing function. Control and enucleated mice showed similar tone detection sensitivity and frequency discrimination in a conditioned lick suppression test. Both groups showed normal reactivity to sound as measured by ASR in a quiet background. However, when startle-eliciting stimuli were presented in noise, enucleated mice showed decreased ASR amplitude relative to controls. Control and enucleated mice displayed no significant differences in ASR habituation, PPI tests, or ABR thresholds, or wave morphology. Our findings suggest that while adult-onset visual deprivation induces cross-modal plasticity at the synaptic and circuit levels, it does not substantially influence simple auditory behavioral performance.

Efficacy of stimulus intensity increases and decreases as inhibitors of the acoustic startle response

The human startle eyeblink response can be inhibited by a change in the stimulus environment briefly before the startling stimulus; both stimulus presentation (prepulse) and cessation of background sound (gap) can result in startle inhibition. More intense prepulses often result in greater inhibition, and this study (N = 53 college students) examined whether graded decreases in sound energy relative to a steady background noise (a "partial gap") would follow this same pattern of inhibition. Embedded in a 65 dB steady background noise were 100 dB white noise startle stimuli preceded at 120 ms on some trials by stimulus intensity increases or decreases of 5, 10, or 15 dB relative to background. Results showed that startle inhibition was graded by amount of change relative to background, such that greater increases or decreases resulted in greater inhibition. Also, increases were more effective startle inhibitors than decreases at equivalent levels of change from background. These results demonstrate that the neural centers responsible for startle inhibition are responsive to both increases and decreases in stimulus intensity, and are sensitive to amount of change, not simply whether a change occurs. These findings may have implications for the development of a screening method for a hearing disorder called tinnitus.

Addressing variability in the acoustic startle reflex for accurate gap detection assessment

The acoustic startle reflex (ASR) is subject to substantial variability. This inherent variability consequently shapes the conclusions drawn from gap-induced prepulse inhibition of the acoustic startle reflex (GPIAS) assessments. Recent studies have cast doubt as to the efficacy of this methodology as it pertains to tinnitus assessment, partially, due to variability in and between data sets. The goal of this study was to examine the variance associated with several common data collection variables and data analyses with the aim to improve GPIAS reliability. To study this the GPIAS tests were conducted in adult male and female CBA/CaJ mice. Factors such as inter-trial interval, circadian rhythm, sex differences, and sensory adaptation were each evaluated. We then examined various data analysis factors which influence GPIAS assessment. Gap-induced facilitation, data processing options, and assessments of tinnitus were studied. We found that the startle reflex is highly variable in CBA/CaJ mice, but this can be minimized by certain data collection factors. We also found that careful consideration of temporal fluctuations of the ASR and controlling for facilitation can lead to more accurate GPIAS results. This study provides a guide for reducing variance in the GPIAS methodology - thereby improving the diagnostic power of the test.

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

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.

An acoustic startle-based method of assessing frequency discrimination in mice

The acoustic startle response (ASR) is a reflexive contraction of skeletal muscles in response to a loud, abrupt acoustic stimulus. ASR magnitude is reduced if the startle stimulus is preceded by a weaker acoustic or non-acoustic stimulus, a phenomenon known as prepulse inhibition (PPI). PPI has been used to test various aspects of sensory discrimination in both animals and humans. Here we show that PPI of the ASR is an advantageous method of assessing frequency discrimination. We describe the apparatus and its performance testing frequency discrimination in young CD1 mice. Compared to classical conditioning paradigms, PPI of the ASR is less time consuming, produces robust results, and can be used without training even in young animals. This approach can be used to investigate the neuronal mechanisms underlying frequency discrimination, its maturation during development, and its relationship to tonotopic organization.

Prepulse inhibition of the startle eyeblink as an indicator of temporal summation

The inhibition of the human startle eyeblink response was assessed in three experiments in which the duration of the prepulse was manipulated. In all cases, inhibition of startle was more pronounced as prepulse duration increased from 6 to 50 msec. Inhibition of startle amplitude for single prepulses was not significantly different from that for paired prepulses (Experiment 1), but inhibition was more pronounced as prepulse intensity increased (Experiment 3). Varying the interval between prepulse offset and startle-stimulus onset had no significant effect on inhibition (Experiment 2). These data demonstrate the sensitivity of startle inhibition to prepulse duration, and suggest that this response system can be used to evaluate early temporal summation in the auditory system.

Prepulse inhibition of the acoustic startle reflex using visual and auditory prepulses: disruption by apomorphine

The amplitude of the acoustic startle reflex can be reduced reliably when preceded at short intervals by a weak stimulus (prepulse) which itself does not elicit startle. The magnitude of this prepulse inhibition effect is attenuated by several dopamine agonists, such as apomorphine, especially when there is a relatively small difference between the intensity of the prepulse and the intensity of the background noise over which the prepulse is superimposed. One goal of the present experiment was to test the generality of this disruptive effect of apomorphine on prepulse inhibition by using either an auditory prepulse that included both a change in intensity and a change in frequency relative to the background noise or a visual prepulse stimulus. Apomorphine reduced auditory prepulse inhibition when induced by a small change in stimulus intensity, but not when induced by a change in both intensity and frequency. Apomorphine consistently reduced visual prepulse inhibition with a complete blockade at 100-ms test interval. However, it did not fully block the usual reduction in startle onset latency or even attenuate the increase in startle amplitude when a visual prepulse was presented 5, 10 or 15 ms before the startle stimulus. Consistent with conclusions from other laboratories using auditory prepulse inhibition, these data suggest that apomorphine did not prevent the animal from detecting prepulse presentation under conditions where the drug completely blocked prepulse inhibition. Moreover, they indicate that the blockade of prepulse inhibition by apomorphine was independent of prepulse modality, adding generality to the original finding. Visual prepulse inhibition may be a useful alternative procedure for evaluating the effects of drugs on this attentional process.

Modification of acoustic and tactile startle by single microwave pulses

Single microwave pulses at 1.25 GHz were delivered to the head and neck of male Long-Evans rats as a prestimulus to acoustic and tactile startle. For acoustic startle, pulses averaging 0.96 microsecond in duration were tested with two specific absorption rate (specific absorption) ranges, 15.0-30.0 kW/kg (16.0-44.2 mJ/kg) and 35.5-86.0 kW/kg (66.6-141.8 mJ/kg), delivered 201, 101, 51, 3, and 1 ms before and 1 ms after onset of a startling noise. The low-intensity pulse did not affect peak amplitude, integral, or latency of the whole-body startle response. The high-intensity pulse at 101 and 51 ms inhibited the startle response by decreasing peak amplitude and integral; at 201 and 51 ms latency was increased. The high-intensity pulse at 1 ms enhanced the startle response by increasing peak amplitude and at 3 ms by increasing integral. For tactile startle, either microwave pulses averaging 7.82 microseconds in duration and 55.9-113.3 kW/kg (525.0-1055.7 mJ/kg) or 94 dB SPL clicks were delivered 157, 107, 57, and 7 ms before and 43 ms after onset of a startling air burst. The microwave pulse at 57 ms inhibited the startle response by decreasing peak amplitude; at 157, 107, 57, and 7 ms it increased latency. The microwave pulse at 43 ms after onset enhanced the startle response by increasing peak amplitude. The acoustic click at 157 and 57 ms inhibited the startle response by decreasing peak amplitude; at 157,2 107, and 57 ms it increased latency.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulatory influence of continuous tone, tone offset, and tone onset on the human acoustic startle response

Startle modulation in young adult men, by continuous background tone and its offset, a 2-s sustained tone and its offset, and the onset of a 25-ms tone pip were compared. Tone (75dB 1000 Hz) offset and onset occurred either 2000 ms or 100-120 ms before the startle stimuli (104dB (SPL), 50-ms white noise bursts). Blink amplitude and latency were unaffected by continuous background tone. Blink amplitude was reliably inhibited by 100-ms offset of both the continuous background tone and the 2-s sustained tone or 120-ms onset of the tone pip, whereas effects on latency were more variable. Facilitation of blink amplitude and latency was significant but weak and only following the 2-s sustained tone, and only with respect to one of two experimental contexts. These findings support those of others and suggest that startle inhibition results from activation of neurons responding to transient environmental changes. The degree of inhibition appears to be related to stimulus value. Startle amplitude facilitation following long sustained prestimulation intervals is dependent on experimental context. Overall latency and amplitude modulation tend to be concordant, leading to the conclusion that the mechanism(s) underlying both are context dependent and linked in the adult human.

Directed attention influences the modification of startle reflex probability

The present study was designed to investigate the effect of directed attention on elicitation and modification of the startle reflex. 30 adult human subjects received 90 dB(A) broadband noise startle stimuli either alone or preceded by a 60 dB(A) prepulse (either 2000-Hz tone, 1000-Hz tone, or broadband noise). Subjects were instructed to attend to one of the three prepulses during half the trials and to ignore all stimuli during the rest of the trials. The probability of responding while attending to a prepulse was significantly lower than the probability of responding while ignoring the prepulses. Responding to the prepulses was also more probable while subjects were attending to the prepulses, and these effects were more pronounced for tone than for noise prepulses. These results suggest that directed attention can influence the probability of the startle reflex without influencing startle amplitude or latency.