Rate influences on tone burst summating potential amplitude in electrocochleography: clinical and experimental data

Electrocochleographic recordings of action and summating potentials are wid ely used in the electrophysiological assessment of endolymphatic hydrops (E LH). Increased amplitudes of the summating potential (SP) in response to to ne burst stimuli are indicative of positive ELH. This study reports the eff ect of repetition rate of tone burst stimulation on the SP amplitude. Using transtympanic electrocochleography (ECochG), the SP in response to 1 kHz t one bursts was recorded in both a Meniere and a non-Meniere population. Abs olute values of the SP were systematically higher in the Meniere group. Mor eover, in the Meniere and non-Meniere groups, the response amplitudes of th e SP at a repetition rate of 8.4 tone bursts/s were only 66 and 32%, respec tively, of the maximal response amplitude which was obtained at the rate of 37.4 tone bursts/s. Additionally, in normal guinea pigs chronically implan ted with a round window electrode, the SP was recorded to 0.5-16 kHz tone b urst stimulations presented at 100 dB SPL with the same different repetitio n rates. Similar enhancement of the SP amplitude was observed from 8.4 to 3 7.4 stimuli/s, whatever the frequency. This effect is interpreted as an inc reased asymmetry of vibration of the cochlear partition, whose mechanical o perating point would not return to the normal resting position at high repe tition rates, since it is permanently shifted in ELH. (C) 2001 Elsevier Sci ence B.V. All rights reserved.