Chronic Bilateral Cochlear Implant Stimulation Partially Restores Neural Binaural Sensitivity in Neonatally-Deaf...

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Developmental Neuroscience

Background:

• Prelingual hearing loss impairs interaural time difference (ITD) sensitivity in cochlear implant (CI) users.
• Neonatal deafness degrades neural ITD sensitivity in the inferior colliculus (IC), similar to CI users.
• ITDs are vital cues for sound localization and speech intelligibility in noise.

Purpose of the Study:

• To investigate if chronic bilateral CI stimulation during development can restore ITD sensitivity in early-onset deafness.
• To assess the impact of early CI stimulation on neural ITD sensitivity and temporal coding in the IC.
• To determine the role of early auditory experience in the maturation of binaural auditory circuitry.

Main Methods:

• Neonatally deafened rabbits received chronic bilateral cochlear implant (CI) stimulation and behavioral training during development.
• Electrophysiological recordings were performed in the inferior colliculus (IC) to measure neural ITD sensitivity.
• Comparison of ITD sensitivity between early-deaf stimulated rabbits, early-deaf unstimulated rabbits, and adult-deaf (AD) rabbits.

Main Results:

• Chronic bilateral CI stimulation partly restored the prevalence of ITD-sensitive neurons in early-deaf rabbits to levels seen in adult-deaf rabbits.
• A partial improvement in neural ITD sensitivity was observed in stimulated early-deaf rabbits compared to unstimulated ones.
• CI stimulation did not improve temporal coding in the early-deaf rabbits.

Conclusions:

• Early bilateral CI stimulation can functionally restore interaural time difference (ITD) sensitivity in the auditory midbrain.
• This study provides the first evidence of functional restoration of ITD sensitivity with CI stimulation in single neurons.
• Early binaural auditory experience is critical for the proper maturation of the brain's binaural circuitry.