Electrical stimulation of the auditory system in animals profoundly deaf from birth

Animals homozygous for the recessive deafness gene (dn/dn) have been used to study central responses to modiolar or round window electrical stimulation. Inferior colliculus evoked responses to contralateral constant current pulses are larger in mutants than in controls. In mutants, responses are largest in animals aged 5-7 months, compared with animals aged 42-50 days or 13.5-19 months. The spiral ganglion cell density is normal in the youngest group, but decreases significantly in older animals. Electrical stimulation of the round window is less effective than modiolar stimulation. Single unit recordings suggest that the larger evoked responses in deafness mice are produced by stronger discharges in neurones, rather than greater synchrony of discharge. The deafness mutation appears to provide a useful animal model for studying electrical stimulation of a central pathway which has never received stimulus-related input.