Morphology variations of click-evoked auditory brainstem response with low and high rate stimuli in rat

Abstract

Background and Aim: The auditory brainstem response (ABR) is one of the most common obj­ective hearing tests conducting in animal and human. The purpose of this study was evalua­ting the morphology variations of ABR wave­forms in rats with low and high rate click sti­muli.

Methods: First, rats with ABR thresholds hig­her than 55 dB SPL were excluded and total 81 ears remained in study. Absolute and interpeak latencies of wave I, II, IV were evaluated at low (17.7 Hz) and high rate (88.7 Hz) for click sti­muli at 120 dB SPL.. Results: At low rate stimuli, ABR waveforms showed different morphologies. The most com­mon complex for waves II to IV was wave III placed on downward slope of wave II (71% of cases). Almost the same morphologies were seen at higher rate; but in some waves, it rou­nded and decreased amplitude. For waves IV-V, the most common morphology was equal amp­litude of wave IV and V in low and high rates (35% vs 56%, respectively). Generally, the high rate stimuli didn’t severely change morphology patterns except for later waves. Conclusion: Normal click-evoked ABR could result in different waveforms. Using click sti­muli at low and high rate result in different mor­phology patterns. Recognizing morphology var­iations of ABR waveforms are essential for det­ecting any pathological conditions. The high rate stimuli increased latencies, especially for later waves.