Abstract
BackgroundSimultaneous bilateral cochlear implantation promotes symmetric development of bilateral auditory pathways but binaural hearing remains abnormal. To evaluate whether bilateral cortical processing remains impaired in such children, cortical activity to unilateral and bilateral stimuli was assessed in a unique cohort of 16 children who received bilateral cochlear implants (CIs) simultaneously at 1.97 ± 0.86 years of age and had ~4 years of CI experience, providing the first opportunity to assess electrically driven cortical development in the absence of reorganized asymmetries from sequential implantation.MethodsCortical activity to unilateral and bilateral stimuli was measured using multichannel electro‐encephalography. Cortical processing in children with bilateral CIs was compared with click‐elicited activity in 13 normal hearing children matched for time‐in‐sound. Source activity was localized using the Time Restricted, Artefact and Coherence source Suppression (TRACS) beamformer method.ResultsConsistent with dominant crossed auditory pathways, normal P1 activity (~100 ms) was weaker to ipsilateral stimuli relative to contralateral and bilateral stimuli and both auditory cortices preferentially responded to the contralateral ear. Right hemisphere dominance was evident overall. Children with bilateral CIs maintained the expected right dominance but differences from normal included: (i) minimal changes between ipsilateral, contralateral and bilateral stimuli, (ii) weaker than normal contralateral stimulus preference, (iii) symmetric activity to bilateral stimuli, and (iv) increased occipital lobe recruitment during bilateral relative to unilateral stimulation. Between‐group contrasts demonstrated lower than normal activity in the inferior parieto‐occipital lobe (suggesting deficits in sensory integration) and greater than normal left frontal lobe activity (suggesting increased attention), even during passive listening.ConclusionsTogether, findings suggest that early simultaneous bilateral cochlear implantation promotes normal‐like auditory symmetry but that abnormalities in cortical processing consequent to deafness and/or electrical stimulation through two independent speech processors persist.
Highlights
The goal of recommending two cochlear implants (CIs) (Papsin & Gordon, 2008; Peters, Wyss, & Manrique, 2010; Ramsden et al, 2012) in children with bilateral deafness is to promote development of hearing with both ears, and to provide benefits of binaural hearing
This study evaluated whether cortical development with bilateral CIs provided early and simultaneously in children with prelingual deafness parallels development in normal hearing children
Based on physiological evidence and behavioral outcome measures, we hypothesized that changes in cortical activity between unilateral and bilateral stimuli would be smaller in children with bilateral CIs relative to normal hearing children, and that cortical activity for bilaterally presented sounds would be abnormal in children with CI
Summary
The goal of recommending two cochlear implants (CIs) (Papsin & Gordon, 2008; Peters, Wyss, & Manrique, 2010; Ramsden et al, 2012) in children with bilateral deafness is to promote development of hearing with both ears, and to provide benefits of binaural hearing. Unilateral hearing leads to abnormal strengthening of pathways from the hearing ear and higher than normal cortical activity in the hemisphere contralateral to the hearing ear (Gordon et al, 2013; Kral, Hubka, Heid, & Tillein, 2013). Such asymmetries manifest in behavioral outcomes such as sound lateralization and speech perception abilities (Gordon, Deighton, Abbasalipour, & Papsin, 2014; Gordon, Henkin, & Kral, 2015; Gordon & Papsin, 2009; Gordon et al, 2013; Jiwani, Papsin, & Gordon, 2016). Based on physiological evidence and behavioral outcome measures, we hypothesized that changes in cortical activity between unilateral and bilateral stimuli would be smaller in children with bilateral CIs relative to normal hearing children, and that cortical activity for bilaterally presented sounds would be abnormal in children with CI
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