Spiral Ganglion Cell Counts Research Articles

Estimation of surviving spiral ganglion cells in the deaf rat using the electrically evoked auditory brainstem response

A procedure was developed to record the electrically evoked auditory brainstem response (EABR) in the rat with sufficiently little stimulus artifact to permit systematic measurements of the first positive wave (P 1), the compound action potential (CAP) of the auditory nerve. Our principal aim was to verify the theoretical prediction that maximum P 1 amplitude is directly proportional to the number of excitable auditory nerve fibers. This was carried out in animals with graded lesions of the spiral ganglion induced by perfusion of the cochlea with different concentrations of neomycin. Two series of observations confirmed the theoretical prediction. Several measures of P 1, including maximum amplitude, and slopes of the P 1 and P 1-N 1 growth functions, were highly correlated with the number of surviving spiral ganglion cells. Correlation coefficients (r) ranged from 0.75 to 0.92. Amplitudes of the later waves exhibited much lower correlations with spiral ganglion cell counts. These findings suggest that measurement of the CAP in deaf humans, possibly as wave I of the EABR, should provide quantitative information about the status of the nerve, which could be useful in screening candidates for cochlear implants, prescribing the optimum device for individual patients, and determining how benefits derived from such devices relate to the condition of the auditory nerve.

Survival of spiral ganglion cells in profound sensorineural hearing loss: implications for cochlear implantation.

Ninety-three temporal bones from 66 patients who were profoundly deaf during life were reconstructed by analysis of serial light microscopic sections. The correlations of total and segmental spiral ganglion cell counts with age, duration of hearing loss and profound deafness, and cause of hearing loss were evaluated. Bivariate analysis demonstrated that total spiral ganglion cell count tended to be lower in older than in younger deaf individuals and lower with longer duration of hearing loss and total deafness. However, multiple regression analysis demonstrated that the cause of hearing loss was the single most significant determinant of total spiral ganglion cell count. Patients with deafness due to aminoglycoside toxicity or sudden idiopathic deafness had the highest residual spiral ganglion cell count and patients with deafness due to presumptive postnatal viral labyrinthitis, bacterial labyrinthitis, and congenital or genetic causes had the lowest numbers of residual spiral ganglion cells.