Tinnitus associated spontaneous otoacoustic emissions. Active outer hair cell movements as common origin?

In the mammalian inner ear, active mechanical processes contribute to cochlear micromechanics. Direct evidence of these are spontaneous otoacoustic emissions (SOAE) which have been registered in the human and animal ear canal. In mammals, outer hair cells (OHC) seem to be the origin of this mechanical energy, because they exhibit motile responses to various stimuli. Here we report on bilateral tinnitus and bilateral SOAE with both acoustical phenomena located in the same frequency range. In a playback of the SOAEs their frequences were identified as the pitch of the tinnitus. An additional criterion favoring a common pathomechanism of SOAEs and tinnitus resulted from masking effects. Tinnitus and SOAEs from both sides were suppressed by the same tone, which indicates that the involved pathways are identical. Therefore we suggest that pathological long-term movements of only a small number of OHCs underlie both phenomena. From the SOAE emission spectra we calculated that not more than 60 OHCs might be involved.