Cross-Modal Functional Reorganization of Visual and Auditory Cortex in Adult Cochlear Implant Users Identified with fNIRS

Figure 5

Model of the influence of cross-modal activation of auditory and visual cortex on CI performance. The -axis shows the amount of cross-modal activation and the -axis shows time after CI implantation. The brown lines represent cross-modal activation in auditory cortex (AC), which is assumed to be maximal at time of implantation and reduces with time. The green lines represent cross-modal activation of visual cortex (VC), which develops rapidly after implantation, when auditory input is restored. The dashed lines indicate low plasticity as expressed with small changes after implantation. The solid lines indicate high plasticity as expressed with large changes after implantation. The area between the respective solid and dashed lines represents the potential variation in plasticity. When considering plasticity levels in visual and auditory cortex together (Bimodal), CI users with a solid green line and a dashed brown line or with a solid brown line and a dashed green line would both be considered good performers since in both cases cross-modal activation in visual cortex is higher than in auditory cortex. However, if one considers each sensory modality separately (Unimodal), the prediction would vary depending on the sensory modality considered. Specifically, when considering visual cortex only, one would expect the CI user with a solid green line and a dashed brown line to perform significantly better than the CI user with a solid brown line and a dashed green line. However when considering auditory cortex alone, one would expect the opposite. This ambiguity is resolved with the currently proposed Bimodal model.