Microsecond Interaural Time Difference Discrimination Restored by Cochlear Implants After Neonatal Deafness

Cochlear implants (CIs) can restore a high degree of functional hearing in deaf patients however spatial hearing remains poor, with many early deaf CI users reported to have no measurable sensitivity to interaural time differences (ITDs) at all. Deprivation of binaural experience during an early critical period is often blamed for this shortcoming. However, we show that neonatally deafened rats provided with precisely synchronized CI stimulation in adulthood can be trained to localize ITDs with essentially normal behavioral thresholds near 50 μs. Furthermore, neonatally deaf rats show high physiological sensitivity to ITDs immediately after binaural implantation in adulthood. The fact that our neonatally deaf CI rats achieved very good behavioral ITD thresholds while prelingually deaf human CI patients usually fail to develop a useful sensitivity to ITD raises urgent questions about whether shortcomings in technology or treatment may be behind the usually poor binaural outcomes for current binaural CI patients.