Alternating electrical-resistance changes in the guinea-pig cochlea caused by acoustic stimuli

Abstract

A new method for measuring electrical-impedance changes elicited by tonal stimuli in the cochlea of the anesthetized guinea-pig was developed. Constant-amplitude currents of low-frequency sinusoidal waveform were delivered to the scala media simultaneously with tonal stimuli. In the signal recorded from the scala media, energy was detected at frequencies equal to the sum and difference of the applied frequencies. This energy was interpreted as due to changes .DELTA.R in the resistance of the scala media synchronized with the acoustic waveform. The maximum magnitude of the change varied from about 0.2% in turn I to about 1% in turn III. During normal conditions, striking parallels existed between the behavior of .DELTA.R and CM as both frequency and intensity were varied. Under asphyxic conditions, the observed change in .DELTA.R was usually much less than that in CM. The results were qualitatively, though not quantitatively, consistent with a 2-dimensional, variable-resistance model of the cochlea.