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      Neural correlates of visual stimulus encoding and verbal working memory differ between cochlear implant users and normal‐hearing controls


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          A common concern for individuals with severe‐to‐profound hearing loss fitted with cochlear implants (CIs) is difficulty following conversations in noisy environments. Recent work has suggested that these difficulties are related to individual differences in brain function, including verbal working memory and the degree of cross‐modal reorganization of auditory areas for visual processing. However, the neural basis for these relationships is not fully understood. Here, we investigated neural correlates of visual verbal working memory and sensory plasticity in 14 CI users and age‐matched normal‐hearing (NH) controls. While we recorded the high‐density electroencephalogram (EEG), participants completed a modified Sternberg visual working memory task where sets of letters and numbers were presented visually and then recalled at a later time. Results suggested that CI users had comparable behavioural working memory performance compared with NH. However, CI users had more pronounced neural activity during visual stimulus encoding, including stronger visual‐evoked activity in auditory and visual cortices, larger modulations of neural oscillations and increased frontotemporal connectivity. In contrast, during memory retention of the characters, CI users had descriptively weaker neural oscillations and significantly lower frontotemporal connectivity. We interpret the differences in neural correlates of visual stimulus processing in CI users through the lens of cross‐modal and intramodal plasticity.


          People with hearing loss who have a cochlear implant (CI) have altered neural processing when engaged in a visual working memory task. During the visual stimulus encoding, CI users had greater visual and auditory cortex activation compared with normal‐hearing controls. Greater connectivity between temporal and frontal areas was observed for CI users compared with normal‐hearing controls.

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          Controlling the False Discovery Rate: A Practical and Powerful Approach to Multiple Testing

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            An automated labeling system for subdividing the human cerebral cortex on MRI scans into gyral based regions of interest.

            In this study, we have assessed the validity and reliability of an automated labeling system that we have developed for subdividing the human cerebral cortex on magnetic resonance images into gyral based regions of interest (ROIs). Using a dataset of 40 MRI scans we manually identified 34 cortical ROIs in each of the individual hemispheres. This information was then encoded in the form of an atlas that was utilized to automatically label ROIs. To examine the validity, as well as the intra- and inter-rater reliability of the automated system, we used both intraclass correlation coefficients (ICC), and a new method known as mean distance maps, to assess the degree of mismatch between the manual and the automated sets of ROIs. When compared with the manual ROIs, the automated ROIs were highly accurate, with an average ICC of 0.835 across all of the ROIs, and a mean distance error of less than 1 mm. Intra- and inter-rater comparisons yielded little to no difference between the sets of ROIs. These findings suggest that the automated method we have developed for subdividing the human cerebral cortex into standard gyral-based neuroanatomical regions is both anatomically valid and reliable. This method may be useful for both morphometric and functional studies of the cerebral cortex as well as for clinical investigations aimed at tracking the evolution of disease-induced changes over time, including clinical trials in which MRI-based measures are used to examine response to treatment.
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              Dementia prevention, intervention, and care


                Author and article information

                Eur J Neurosci
                Eur J Neurosci
                The European Journal of Neuroscience
                John Wiley and Sons Inc. (Hoboken )
                09 July 2021
                August 2021
                : 54
                : 3 ( doiID: 10.1111/ejn.v54.3 )
                : 5016-5037
                [ 1 ] Evaluative Clinical Sciences Platform Sunnybrook Research Institute Toronto Ontario Canada
                [ 2 ] Department of Physiology University of Toronto Toronto Ontario Canada
                [ 3 ] Otolaryngology—Head and Neck Surgery Sunnybrook Health Sciences Centre Toronto Ontario Canada
                [ 4 ] Faculty of Medicine, Otolaryngology—Head and Neck Surgery University of Toronto Toronto Ontario Canada
                [ 5 ] Department of Psychology Ryerson University Toronto Ontario Canada
                Author notes
                [*] [* ] Correspondence

                Andrew Dimitrijevic, Evaluative Clinical Sciences Platform, Sunnybrook Research Institute, 2075 Bayview Ave, Toronto, ON M4N 3M5, Canada.

                Email: andrew.dimitrijevic@ 123456sunnybrook.ca

                Author information
                © 2021 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                : 10 June 2021
                : 09 November 2020
                : 14 June 2021
                Page count
                Figures: 8, Tables: 1, Pages: 22, Words: 16595
                Funded by: Mason Scientific Discovery Fund
                Research Report
                Cognitive Neuroscience
                Custom metadata
                August 2021
                Converter:WILEY_ML3GV2_TO_JATSPMC version:6.0.7 mode:remove_FC converted:22.09.2021

                cochlear implant,connectivity,hearing loss,neural oscillations,verbal working memory,visual processing


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