A Parametric Study of the N40 Auditory Evoked Response in Rats

Background: The N40 auditory evoked potential (EP) in rats is used to study “sensory gating.” Our first goal was to compare the effects of systematically varying the characteristics of the pairs of clicks (S1–S2), on the degree of attenuation of the responses to S2 stimuli. A second goal was to examine the effects of changing S2 stimuli on the degree of attenuation of the responses to the deviant stimulus. Methods: The N40 EP was recorded from 10 rats in eight identical-pair conditions and from 11 rats in two paradigms: nonidentical pairs and short trains of identical stimuli followed by a deviant stimulus. Results: In eight identical-pair conditions changing stimulus duration, intensity, or frequency had no effect on the degree of attenuation of S2 responses. Changing S2 stimulus or presenting a deviant stimulus following a train of identical stimuli had a significant effect on the degree of attenuation of the response to the deviant stimulus. Conclusions: We conclude that the rat N40 EP is sensitive to stimulus change and can contribute to the study of both habituation and dishabituation mechanisms of “sensory gating.”