The modulation of the sensitivity of the mammalian cochlea by low frequency tones. II. Inner hair cell receptor potentials

Abstract

Abstract Intracellular receptor potentials from inner hair cells and extracellular potentials within the tunnel of Corti immediately outside inner hair cells have been recorded in the first turn of the guinea pig cochlea. The a.c. and d.c. components of these receptor potentials elicited by high frequency tones within the tip of the isoamplitude tuning curve were modulated in synchrony with a simultaneously applied low frequency suppressor tone. The observed suppression was largest for peak low frequency displacements of the cochlear partition towards scala tympani and less pronounced for displacements towards scala vestibuli. Little suppression was observed at intermediate phases of the low frequency suppressor tone corresponding to the zero crossings of the low frequency motion of the cochlear partition. Receptor potentials elicited by high frequency tones in the tail region of the isoamplitude curve were also modulated, but less strongly and in the opposite phase (scala vestibuli) to the response to frequencies close to the characteristic frequency of the inner hair cell. The modulation for frequencies much below the characteristic frequency also occurred only over a very limited range of high frequency tone intensity. Suppression of the microphonic response to the low frequency tone by the high frequency stimulus was also observed.