Asymmetric Cortical Activation in Adolescents with Sequential Bilateral Cochlear Implants and Long Inter-Implant Intervals

Background: Unilateral cochlear implantation (CI) in early childhood results in relative normal auditory pathway maturation of the first implanted side. Little is known about the cortical consequences of prolonged unilateral auditory deprivation when a second CI is provided in adolescence.

Objective: To gain insight in the effects of long inter implant intervals (more than 5 years) in adolescents with unilateral CIs on cortical maturation.

Methods: Cortical potentials were recorded in 14 deaf subjects, who received their first CI early in childhood or after a period with adequate residual hearing, and their second CI after in interval of 4 to 16 years. Responses were recorded from each ear, one year after activation of their second CI.

Results: Ten patients who received their first CI early in life demonstrated relative normal cortical activation. Stimulation of their second implant revealed an immature cortical activation. This was associated with poor speech perception and even non-use of their device. Three younger children, aged 10-13.5, had maturing cortical waveforms which were age appropriate for their first implanted ear and demonstrated a delayed maturation for their second ear.

Conclusion: Prolonged unilateral auditory deprivation in children with CIs causes structural changes in cortical maturation which persists after one year hearing experience with bilateral CIs.