Enhancement and depression of tactile and acoustic startle reflexes with variation in background noise level

Abstract

The amplitude ofthe acoustic startle reflex in the rat is related to the level ofbroadband background noise by an inverted-U-shaped function. We tested the hypotheses that (1) the initial increment, (2) the subsequent decrement, or (3) the entire function results from a nonspecific noise effect on reflex expression, as would be indicated by a common effect across reflexes elicited by acoustic and nonacoustic stimuli. Responses to electrotactile, airpuff, and acoustic startle stimuli were measured, each in aseparate group of rats, in noise levels varying from 60 to 100 dB. A biphasic effect of noise on the acoustic startle reflex was observed, with a modest increase from 60 to 70 or 80 dB, and a decline thereafter. In contrast, electrotactile startle provided a monotonie increase in amplitude to a maximum at 90 or 100 dB, whereas airpuff startle showed a progressive decline in amplitude, with an increase in background level beyond the optimal value at 60 to 70 dB. The latter effects demonstrated an unexpected division between facilitation versus reflex depression within the tactile modality, but subsequent data demonstrated that the effective component of the airpuff was acoustic, rather than tactile, in nature. The overall empirical conclusion is that facilitation by noise is nonspecific, whereas reflex depression that appears at noise levels beyond 70 to 80 dB is specific to acoustic stimuli. These findings suggest that reflex facilitation results from motor excitation and that reflex depression results from a partial masking of the eliciting stimulus.

Spectral frequency and the modulation of the acoustic startle reflex by background noise.

“…Despite these difficulties, the sensory masking hypothesis can explain many aspects of these behaviors, for example, the results concerning the interaction of startle stimulus intensity and background noise level obtained by Davis (1974), the data of Experiment 3 showing that the response to a low-frequency startle stimulus is reduced in the presence of an intense low-frequency band-pass noise, and the reduced response with the combination of a high-frequency startle stimulus with an intense high-frequency background. This hypothesis is also supported by other results showing that the downturn in startle responsivity in a broadband noise does not occur when the reflex is elicited by a sudden brief electric shock (Ison & Russo, in press). These successful applications of sensory masking to understanding the startle literature suggest the value of reexamining the conditions of present experiments to see if they do provide a fair test of the hypothesis.…”

Modification of the acoustic startle response in hearing-impaired C57BL/6J mice: Prepulse augmentation and prolongation of prepulse inhibition.

“…By contrast, the study by Hoffman and Wible (1970) was conducted in a quiet background, and the studies by Hoffman and Searle (1968) and Stitt et al (1976) used S1s of only 70 dB SPL. A 70-dB background noise markedly enhances ASR amplitude (Corey & Ison, 1979; Davis, 1974; Hoffman, Marsh, & Stein, 1969; Ison & Russo, 1990), and the effectiveness of S1 as a modifier of the ASR is directly related to its intensity (Hoffman & Ison, 1980; Ison & Hammond, 1971). Thus it may be that in normal-hearing rats, the occurrence of PPA is made more likely when startle circuits are “hyperfacilitated” by background noise and/or an intense S1.…”

Habituation of the Acoustic and the Tactile Startle Responses in Mice: Two Independent Sensory Processes.

“…The production of pure tactile airpuff stimuli involves technical difficulties arising from the solenoid controlling the airflow and the noise produced by the airpuff itself when hitting the subject, both of which produce strong additional acoustic signals (Ison & Russo, 1990). This acoustic artifact of the tactile stimulus strongly influences the TSR, as shown by Taylor et al (1991).…”

“…Because it was shown that acoustic and tactile input summate (Li & Yeomans, 1999; Schmid et al, 2003) and because tactile airpuff stimuli have been shown to have a relevant acoustic component (Flaten & Blumenthal, 1998; Ison & Russo, 1990; Taylor, Casto, & Printz, 1991; Woodworth & Johnson, 1988), we carefully controlled acoustic and other influences on TSR habituation. In our study, Experiment 3 is the main experiment exploring generalization of habituation across stimulus modalities, whereas the other experiments (1, 2, and 4) were done to guarantee that the results of Experiment 3 can be generalized.…”