Testing for “Recruitment” by Electrocochleography

Abstract

Normal electrocochleographic (E.Co.G.) tracings were compared with those showing characteristics which resemble audiometric recruitment. The normal E.Co.G. shows two major features as click levels are raised: 1) Over the intensity range from 0–80 dB H.L., for the click, the VIII nerve action potential (AP) latency decreases from approximately 4 to 1.5 msec; and 2) at low click levels, the AP wave-form is diphasic, and shows a slow growth with increasing intensity, while at higher levels, the AP wave-form is monophasic and increases more rapidly with increases in sound level. Yoshie has referred to the low and high intensity portions of the AP amplitude curve as the L and H curves, respectively. In patients showing the “recruiting responses”, the threshold for the click is elevated and the latency is reduced at threshold. The wave-form of AP is diphasic over the entire intensity range, and AP amplitude grows much more rapidly than in the normal case. It appears that these “recruiting” responses represent the H curve of Yoshie with the L curve removed. The differences between normal and “recruiting” E.Co.G. responses can be given a tentative interpretation based on current findings on the structure and function of the peripheral auditory receptor.