Human hair cell-VIII nerve transmission deficit: A case study

Abstract

A 12-year-old girl with bilateral moderate pure tone hearing loss (30–50 dB) and profound speech comprehension impairment (0%–30% correct discrimination) was tested with auditory-evoked potentials. No neural components occurred in the brainstem (1–10 ms), mid (10–50 ms), and long-latency (50–250 ms) time domains even though the patient could “hear” the clicks. A cognitive P300 component was evoked during the discrimination of an infrequent tonal signal indicating normal stimulus classification function. Cochlear microphonic activity of normal amplitude was recorded from an ear-canal electrode. Thus, the absence of neural components of auditory-evoked potentials in the presence of preserved receptor (hair cell) function is interpreted as due to an alteration of transmission between hair cell and VIII nerve leading to a loss of synchrony of VIII nerve activity and an absence of evoked potentials. The finding that the patient's temporal discrimination abilities were severely impaired supports such an interpretation: binaural time or intensity cues could not be used for localization; binaural “beats” were absent; monaural resolution of two clicks was markedly slowed.