Assessment of neural and MAP level asymmetries in a large cohort of children with bilateral cochlear implants

Bilateral cochlear implants (BCIs) are provided to children who are deaf in both ears to restore binaural/spatial hearing, but interaural stimulation mismatches can limit potential benefits. This study aimed to: 1) investigate how the programming of stimulation parameters in BCI users differs between bilateral pairs of electrodes, and (2) evaluate the impact of sequential implantation and mismatched array types on asymmetries. A mixed effects modeling analysis assessed cochlear implants (CI) stimulation parameters and peripheral neural responses retrospectively collected (September 2003-July 2022) in 542 children with BCIs (n = 157 sequentially implanted, n = 385 simultaneously implanted, n = 465 with matched perimodiolar arrays, and n = 77 with one perimodiolar and one straight array (mismatched)). Peripheral neural measures were similar between BCIs although asymmetries in auditory nerve thresholds were measured in children implanted sequentially with mismatched arrays (mean(SE) = -2.02(0.90) dB, p < 0.05). Children with sequential BCIs had greater maximum stimulation levels (C-levels) in the first implanted ear than the second (mean(SE) = 1.64(0.03) dB, p < 0.0001) whereas C-levels were similar between ears in children with simultaneous BCIs (mean(SE) = 0.07(0.01) dB, p < 0.0001). Programming asymmetries were comparable between matched and mismatched arrays in sequential BCIs (F(1, 149.9) = 0.01, p = 0.92) and simultaneous BCIs (F(1, 377) = 0.001, p = 0.98). Overall, programming asymmetries reflect implantation sequence more than array type differences. Similar neural responses bilaterally suggest programming asymmetries arise from central effects of prior unilateral hearing, consistent with the aural preference syndrome.