Effects of Repetition Rate on Tone Burst Auditory Brainstem Responses in Normal Young Adult Wistar Rats

Abstract

Introduction: The repetition rate of a stimulus serves as a crucial criterion in audiological assessments for differential diagnosis in certain special populations. Therefore, this study aimed to evaluate the normal variation of auditory brainstem response (ABR) parameters, including latency, amplitude, morphology, and component duration (width), using two different rates of tonal stimuli with varying frequencies in Wistar rats.

Materials and Methods: In this experimental study, 45 young adult male Wistar rats were subjected to ABR measurements using tone burst stimuli at octave frequencies ranging from 2 to 16 kHz, with two rates of 11.1 and 57.1/s, following the relevant protocols. The stimuli were delivered at an intensity of 80 dB SPL and through a speaker.

Results: At a high rate, latency changes in later waves were greater than those in earlier components, whereas amplitude changes in later waves were smaller than those in earlier ones. Rate-dependent changes, as a function of frequency, were uniform for both latency and amplitude. Morphologically, ABR components were broadened in a frequency-dependent way. The duration of wave I was shorter than that of wave IV, and the wave duration changes were influenced by frequency. These findings were statistically significant (P<0.05).

Conclusion: The results can be attributed to differences in adaptation mechanisms within the auditory system, the additive synapse theory, and desynchronization resulting from increased stimulation rates. Knowledge of the various effects of rate as a function of frequency on ABR parameters in normal rats is essential to understanding how different changes in these parameters at each wave could lead to a more precise diagnosis in neuro-pathological conditions