Fear potentiation of the acoustic startle reflex using noises of various spectral frequencies as conditioned stimuli

The outcome of these experiments indicates that it is easier to employ low-frequency bands of noise to obtain auditory fear-potentiated startle with high-frequency startle-eliciting stimuli.

Abstract

The effectiveness of noise of various intensities and frequencies in modulating the amplitude of the acoustic startle reflex was evaluated, as a preliminary test of the capacity of these noises to produce consistent and reliable fear-potentiated startle in rats. It was determined that bands of noise containing high frequencies (greater than 10 kHz) tend to unconditionally reduce acoustic startle responses, probably by masking the high-frequency startle-eliciting stimulus. Noise containing high frequencies produced reliable fear-potentiated startle only when its estimated unconditioned startle suppression was subtracted from the enhancement obtained after pairing it with footshocks. Noises devoid of high frequencies produced modest-unconditioned startle enhancements and the most robust and reliable fear-potentiated startle when they were paired with footshocks. A nonmonotonic relationship between training shock intensity and the level of fear-potentiated startle was also exhibited when a low-frequency noise was used as a conditioned stimulus, a finding consistent with previous studies in which a visual stimulus was used. Finally, a differential Pavlovian conditioning procedure indicated that rats could readily discriminate between two different low-frequency bands of noise. The outcome of these experiments indicates that it is easier to employ low-frequency bands of noise to obtain auditory fear-potentiated startle with high-frequency startle-eliciting stimuli.