GOOD INTERAURAL TIME DIFFERENCE SENSITIVITY DESPITE DIFFERENT HEARING EXPERIENCE IN COCHLEAR IMPLANTED RATS

Spatial hearing and sound localization are essential for everyday auditory perception, relying primarily on two binaural cues: interaural time and level differences (ITD/ILD). However, for prelingually deaf cochlear implant (CI) users, spatial hearing remains a major challenge, largely due to reduced ITD sensitivity. In contrast, we recently demonstrated that neonatally deafened (ND) rats fitted with bilateral CIs in young adulthood can develop excellent ITD sensitivity when provided with microsecond-accurate stimulation. In the present study, we investigated how different hearing experiences and stimulation modes affect ITD sensitivity by comparing three cohorts: adult deafened (AD) CI rats, ND CI rats, and normal-hearing (NH) rats.
ND and AD rats received CIs in young adulthood and were trained to lateralize electric pulse trains with accurate ITDs in the range of ±120 µs at a clinical pulse rate of 900 pps. NH rats were trained to lateralize ITDs of acoustic clicks at a click rate of 900 Hz. After an initial training, rats were tested on their ITD sensitivity and thresholds were compared.
All rats developed good ITD sensitivity, with thresholds in the sub-millisecond range. Although the lowest thresholds were observed in AD CI rats, all cohorts exhibited robust ITD discrimination, indicating broadly comparable spatial hearing capabilities.
Overall, the rat is an excellent animal model for investigating binaural hearing. Regardless of their early auditory experience, acoustically and electrically hearing rats showed good ITD sensitivity when presented with informative ITDs, thus challenging the hypothesis of an early critical period for the development of spatial hearing.