Cortical Activation Shortly after Cochlear Implantation

Abstract

We evaluated the cortical activations in postlingually deaf cochlear implant (CI) users in the early period (0–2 months) of CI usage. The subjects were 8 early CI users and 8 normal subjects. With tone burst stimuli (1 kHz) delivered to the right side, strong and broad activation of the ipsilateral (right) primary auditory cortex with 2 peaks and weaker activation of the contralateral (left) temporal lobe were observed in early CI users, in a clear contrast with the normal subjects in whom activation was observed in a small area of the contralateral (left) primary cortex. With word stimuli, activation of the superior frontomedian cortex presumably including the supplementary motor area and the neighboring cingulate gyri was observed in early CI users, which was absent in normal subjects. The activation in the immediate association cortices near the primary area was lower in early CI users, while the periphery of the association cortex seemed to be more mobilized.

Unimodal and cross-modal plasticity in the ‘deaf’ auditory cortex

“…Based on current findings in the hearing auditory system (Sakai & Suga, 2002) we assume that the cortical reorganization is the source of subcortical reorganizations and not vice versa (for discussion, compare Kral & Tillein, 2006). Cortical reorganization after cochlear implantation in humans has been shown to extensively include higher-order areas Ito et al, 2004;Lee et al, 2001;Naito et al, 1997).…”

Cortical Plasticity after Cochlear Implantation

“…Reduced input to the brain from impaired auditory pathways results in significant changes in the central auditory system [12] and is accompanied by a recruitment of deprived cortices in response to input from the intact senses [13–17]. When auditory input to the brain is reintroduced, this novel auditory experience may itself induce additional plasticity [18]. The sensory reafferentation provided by the CI thus offers a unique opportunity to study the effects of preceding deafness on functional brain organization.…”

Testing the Diagnostic Value of Electrical Ear Canal Stimulation in Cochlear Implant Candidates by Functional Magnetic Resonance Imaging

“…In previous studies, monaural acoustic stimulation under fMRI or PET had revealed a stronger lateralization of the cortical response towards the contralateral hemisphere and a more restricted activation in normal-hearing subjects compared with monaurally or binaurally deaf subjects, who were stimulated either acoustically or via CI Ito et al, 2004;Scheffler et al, 1998]. Therefore, laterality indices (LI) were calculated for all participants with 'perfect' or 'acceptable' activation as LI = (V contr -V ipsi )/(V contr + V ipsi ), where V contr and V ipsi denote the number of the activated voxels in the contralateral and ipsilateral cortices, respectively.…”

“…With normal-hearing subjects, however, unilateral acoustic stimulation evoked strong contralateralization of cortical fMRI response, and a binaural stimulation evoked a nearly balanced activation [Ito et al, 2004;Scheffler et al, 1998]. described a shift from contralateral activation during normal bilateral hearing to bilateral activation after a sudden unilateral hearing loss due to cochlear nerve resection.…”