Repetition Rate and Auditory Neuropathy

Question

What is the effect of repetition rate on auditory neuropathy? Usually, we are unable to obtain a response at 11.1, 30.1, and at higher repetition rates, though we are sometimes able to obtain a response at low repetition rates. What is the reason? Can you recommend further reading?

Answer

The effect of stimulus rate on the auditory brainstem response has been well established. As stimulus rate is increased, the latency of the ABR also increases and the amplitude decreases. These latency and amplitude changes vary for different components of the ABR; wave I should usually be more resistant to the effects of increasing rate than wave V. The classic paper by Robinson and Rudge (1977) demonstrated the relationship between neurological impairment and an abnormal ABR rate-change function. They tested patients with white-matter disease (multiple sclerosis) and found that the ABR could be absent at stimulus rates greater than 25/s. Another classic paper is that of Lasky (1984) who established ABR rate-functions in premature infants. In the immature auditory system, the latency and amplitude of the ABR is profoundly affected by increasing stimulus rate. These effects diminish with maturation.

It must be remembered that the ABR is composed of several different neural generators including fast wave action-potential type responses from the fiber tracts and slow waves generated by dendritic depolarization. These components of the ABR would have a differential response to stimulus rate. I suspect that at stimulus rates below 10/s that these slow waves that are less dependent upon neural synchrony may become evident. Wave V of the ABR rides on such a slow wave, so it may be more evident when using stimuli at very slow rates. The observation of this "slow" wave will also depend upon the filter settings used for ABR recording. Unfortunately, there has been no research that has established how the presence of ABR at exceptionally low rates (when absent at higher rates) is related to speech, language and hearing outcomes. Certainly, the "appearance" of an ABR for stimulus rates <10/s, indicates a neural type hearing problem, and the absence of "fast" components for higher stimulus rates is a demonstration of the neural dys-synchrony that is a hallmark of auditory neuropathy.

References

Lasky, RE (1984) A developmental study on the effect of stimulus rate on the auditory evoked brain stem response. Electroencephalography and Clinical Neurophysiology 59, 411-419.

Robinson K & Rudge, P (1977) Abnormalities of the auditory evoked potentials in patients with multiple sclerosis. Brain 100, 19-40.

Dr. Barbara Cone-Wesson is associate professor of Speech and Hearing Science at the University of Arizona. She has used electrophysiological methods of auditory system assessment for clinical and research applications for over 25 years.