Are spiral ganglion cell numbers important for speech perception with a cochlear implant?

OBJECTIVE: Studies of factors affecting the survival of ganglion cells in adults with profound hearing loss and speech perception in cochlear implant users are reviewed in order to assess the hypothesis that ganglion cell numbers have a strong influence on the level of speech perception achieved by adult implant users. DATA SOURCES: All histopathologic data have been published as tables or figures in refereed papers. Speech perception data were collected from published papers and directly from clinics and from Cochlear Corporation's database. STUDY SELECTION: Histopathologic studies with reasonably large groups of patients were selected. The speech perception data were from the largest study available. DATA EXTRACTION: All data used have been published in refereed journals of high repute. No other assessment of quality or validity was available to the author. DATA SYNTHESIS: Trends in the speech perception data were compared qualitatively and quantitatively with trends in the histopathologic ganglion cell data.
CONCLUSIONS: The analysis found no strong evidence that spiral ganglion cell numbers have a strong influence on the level of speech perception achieved with a cochlear implant. A possible explanation for this surprising result may be that the minimum number of cells required for good speech perception is quite low, and the majority of implant users exceed this minimum requirement.