Effects of Click Polarity on Brainstem Auditory-Evoked Potentials in Cochlear Hearing Loss: A Working Hypothesis

Abstract

The rarefaction-condensation differential potential (RCDP) obtained by subtracting brainstem auditory-evoked potentials (BAEPs) to C clicks from those to R clicks has been studied in 32 normal subjects and 31 cases of cochlear hearing loss. In normal subjects, no RCDP was recorded along the lower 30–55 dB of the JV latency-intensity function, thus defining the pre-RCDP range. The pre-RCDP range was always abolished in losses unmasking BAEPs from lower (<1 kHz) tonotopic regions. When the BAEP originated from higher (< 1 kHz) tonotopic regions, the pre-RCDP range was either reduced or abolished. These results led to a working hypothesis based on single-unit data and stating a dual dependence of polarity effects on variables distributed along the tonotopic and intensity dimensions, with respective break-points at 1 kHz, and at the junction of the tip and tail of unit frequency tuning curves. The 1 kHz break-point could represent the upper frequency limit for phase locking in man.

Key Words:

• Auditory brainstem response Click polarity
• Latency-intensity function Phase locking
• Frequency tuning curve
• Tip-to-tail difference
• Hearing loss
• Pathophysiology