Effects of motor activity on the elicitation and modification of the startle reflex in rats

In order to examine the effects of efferent processes on the elicitation and modification of startle behavior, we administered startle-eliciting stimuli to rats while they were engaged in spontaneous motor activity. When tone bursts (Experiment 1) or electric shocks (Experiment 2) were used to elicit the reflex, its amplitude was substantially less when the rats were active than when they were quiet. Grooming, face washing, and consuming were associated with the greatest reduction. The ability of a 50-dB auditory prepulse to inhibit a subsequent auditory startle was also reduced during activity (Experiment 3). The amount of inhibition produced by a prepulse was decreased even when the baseline startle responses were equated in quiet and activity by varying the intensity of the eliciting stimulus, indicating that the reduction was not due to an artificial “floor effect” (Experiment 4). The study demonstrated that both sensory and motor events affect reflexive responses in the rat, as is known for the human.