Persistent effect of noise on the acoustic startle reflex in the rat

Abstract

Continuous noise facilitates acoustic startle reflexes in the rat. Rats were exposed to noise for 23 h (Experiment 1) or to 23 h of startle eliciting stimuli at the rate of lImin (Experiment 2). Facilitation was reduced following habituation in Experiment 2, but was unaffected by prolonged noise exposure in Experiment 1. Reflex inhibition produced by a brief noise was not altered by habituation. Prior experiments show that increases in intensity of continuous noise engage two disparate processes which affect the acoustic startle reflex, one facilitatory (arousal) and one inhibitory (masking). The present data reveal that arousal is not diminished by prolonged noise exposure. The loss of facilitation following reflex habituation may be attributed to its increased susceptibility to masking, or to a direct effect of stimulus repetition on the arousal process normally associated with the noise background.The strength of the rat's acoustic startle reflex is affected by variation in the homogeneity and intensity of the acoustic background present at the time of the eliciting stimulus. A steady noise of moderate intensity facilitates the reflex, whereas a punctate noise which immediately precedes the eliciting stimulus inhibits it. The two experiments reported here examined the persistence of these modulating influences following prolonged continuous exposure to the noise and prolonged repetitive exposure to the eliciting stimulus. EXPERIMENT 1The facilitative effect of continuous noise on the rat's acoustic startle reflex is apparent within 100 msec of noise onset and becomes asymptotic within 2,000 msec thereafter (Hoffman & Wible, 1969). It has been concluded that this source of reflex potentiation does not decay when stimulation is maintained beyond 2,000 msec (Davis, 1974). This conclusion follows from an experimental result provided by Hoffman, Marsh, and Stein (1969), who used two background conditions, either pulsed or continuous noise, and found that the advantage of the steady noise was stable over a 6-h exposure period. However, the outcome of this procedure is difficult to interpret because pulsed noise against a silent background inhibits the startle reflex. In the absence of a silent neutral baseline, the experiment provided no conclusive evidence for facilitation: the difference between the two conditions may have been due to inhibition Reprint requests should be directed to Professor James R. Ison, Department of Psychology, University of Rochester, Rochester, New York 14627. This research was supported by grants from the NINCDS, NS-12443, and from the NIEHS, ES-OI247. rather than facilitation. Its stability over the 6-h period might characterize only the inhibitory process, which has been otherwise shown to be a stable phenomenon (Ison, Hammond, & Krauter, 1973). The present experiment provided the appropriate silent background condition as a control and extended the period of exposure to 23 h. The scheduling of tests about 24 h apart avoided effects on pre-and posttests that might occur from a differen...

Effects of background noise on the human startle reflex and prepulse inhibition

“…A third possibility is that the background noise could summate with the startle-eliciting stimulus, thus increasing startle. This hypothesis is supported by animal studies (e.g., Cory & Ison, 1979;Hoffman & Fleshler, 1963). Finally, background noise could decrease the signal-to-noise ratio between an acoustic startle-eliciting stimulus and background noise, thus decreasing startle amplitudes.…”

“…However, the effect of continuous background noise on human startle has, to our knowledge, not been investigated. Animal studies have found that 70‐dB (Cory & Ison, 1979) and 85 dB (Hoffman & Fleshler, 1963) continuous background noise facilitate acoustic startle by up to 100%, compared to ambient background noise. Other studies (e.g., Davis, 1974; Ison & Russo, 1990) did not include an ambient noise level baseline, but found that increases in background noise levels initially increased startle responses followed by a decrease in startle at higher intensities.…”

Structural Alterations in a Rat Model of Short-Term Conductive Hearing Loss Are Associated With Reduced Resting State Functional Connectivity

“…The mean fiber number was insignificantly different after CHL; however, the mean fiber length and mean fiber density for the lateral lemniscus after CHL was significantly decreased compared to before (t-test: t = 2.548, df = 30, p = 0.0162 and t = 2.388, df = 30, and p = 0.0234, respectively). reflex inhibition produced by brief noise exposure (Cory and Ison, 1979;Wu et al, 1984), indicating in the rat a priming or sensitization effect. It is interesting to note, an increased sensitivity to continuous noise results in suppression in the acoustic startle response (ASR) in rats (Rybalko et al, 2019).…”

Sensitization of the rat’s acoustic startle response by repetition of a photic stimulus

“…Davis, Svensson, and Aghajanian (1975), for example, reported that d-and I-amphetamine enhance the reflex sensitizing effects of eliciting stimulus repetition without changing sensitization produced by background white noise. Hoffman, Marsh, and Stein (1969) and Cory and Ison (1979) showed that the latter kind of sensitization persists for durations of background noise exposure of up to 24 h. Together, these various demonstrations suggest caution in assuming that all sources of sensitization or response enhancement reflect the same underlying process.…”