Cochlear potentials of the pigeon inner ear recorded with microelectrodes.

The CM-intensity function (i.e. the relation between the amplitude of the cochlear potential (CM) and the sound pressure level) of the avian ear has previously been shown to deviate from the mammalian ear with respect to the slope of the linear part of the function. The lower slope values found in the perilymphatic space of the avian ear have been interpreted to indicate a damping influence of the tegmentum vasculosum on the mechanical vibration of the basilar membrane. In this study the CM-intensity function has been examined on either side of the tegmentum vasculosum of the pigeon ear using microelectrode technique. The slope of the linear part of the CM-intensity function in scala vestibuli was found to be a function of the sound frequency approaching unity at higher frequencies. In ductus cochlearis the slope of the linear part of the CM-intensity function was close to unity at most frequencies except the best frequency for the electrode position. At this frequency (3-4 kHz) the slope value was low. These findings from the ductus cochlearis are similar to findings in scala media of the mammalian ear. Thus the influence of tegmentum vasculosum on CM in scala vestibuli may be due to passive electrical properties of the tissue and not to the mechanical vibration of the basilar membrane.