Distribution of Microphonic Potentials in the Four Turns of the Guinea Pig Cochlea

Abstract

Frequency selectivity of the recording of cochlear microphonics (CM) with the electrode near the round window is low; the output is dominated by the CM generated in the basal turn. The differential technique of the CM recording, with microelectrodes inserted into the scala tympani and scala vestibuli of individual cochlear turns (Tasaki and Fernandez, 1952; Dallos, 1969) provides better frequency selectivity. Similar results as those with the differential technique may be obtained with the microelectrode introduced into the scala media (Honrubia and Ward, 1968). Although the effect of the CM generators located in other turns is not fully excluded with this type of recording, the results are representative for the estimation of the functional state of the individual cochlear turn and may demonstrate some special properties of the CM, e.g. the shift of the maximum CM voltage towards the base with the increased sound intensity. We attempted in our experiments to repeat some of the Honrubia and Ward measurements and to explore the method for the estimation of the effects of the narrow band noise exposure on the CM in individual turns of the guinea pig cochlea.