Human Auditory Nerve Action Potentials and Brain Stem Evoked Responses: Effects of Audiogram Shape and Lesion Location

Simultaneously recorded auditory nerve action potentials (APs) and brain stem auditory-evoked responses (BSERs) were correlated with audiogram shape and with location of patholgoic condition. High frequency (4 to 8 kHz) hearing loss (1) prolongs AP and BSER latency, (2) shortens the interval between the first AP peak (N1) and the fifth BSER peak (V), and (3) creates relatively large latency differences between condensation and rarefaction responses (thus bringing into question the common practice of combining condensation and rarefaction responses). Ears with retrocochlear deficits in the subjects in the study were detected reliably by prolonged N1 to V interval and increased BSER peak V latency. The reliability of these retrocochlear signs was further increased by allowing for the effects of audiogram shape. Another retrocochlear sign, termed "inappropriate AP preservation," was positive in 40% to 50% of the retrocochlear ears.