Repetition suppression of the rat auditory evoked potential at brief stimulus intervals

An important prerequisite for the development of animal models of human auditory evoked potentials (AEP) is the accurate identification of homology. Prior research has revealed some remarkably similar response properties between rat and human AEPs, although there remains little consensus regarding the nature or validity of this correspondence. In the present study we seek to extend this research by examining the response properties of rat AEP as a function of stimulus repetition and interval. The aim being to determine whether rat AEP components show the same paradoxical reversal of repetition suppression observed for the human N100 AEP component at brief stimulus intervals. To achieve this, AEPs were recorded epidurally at the vertex in the freely moving rat in response to acoustic stimuli presented at random stimulus intervals between 50 and 5,000 ms. Using stimulation and analysis techniques to remove AEP waveform distortion due to overlapping AEP responses, the present results show that rat AEP components can be successfully resolved at intervals as brief as 50 ms. The results also demonstrate several fundamental types of correspondence between human and rat AEP components in terms of the sensitivity to stimulus interval and acoustic stimulus type. However the results found no evidence that rat AEP components show the reversal of repetition suppression at brief, relative to long, stimulus intervals as demonstrated for the N100 component in humans. The results are discussed in terms of EEG recording and AEP analysis procedures that provide promising avenues for future research.