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

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. 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. 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. 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.