Sensory experience modulates the reorganization of auditory regions for executive processing.

Crossmodal plasticity refers to the reorganization of sensory cortices in the absence of their typical main sensory input. Understanding this phenomenon provides insights into brain function and its potential for change and enhancement. Using functional MRI, we investigated how early deafness influences crossmodal plasticity and the organization of executive functions in the adult human brain. Deaf (n = 25; age: mean = 41.68, range = 19-66, SD = 14.38; 16 female, 9 male) and hearing (n = 20; age: mean = 37.50, range = 18-66, SD = 16.85; 15 female, 5 male) participants performed four visual tasks tapping into different components of executive processing: task switching, working memory, planning and inhibition. Our results show that deaf individuals specifically recruit 'auditory' regions during task switching. Neural activity in superior temporal regions, most significantly in the right hemisphere, are good predictors of behavioural performance during task switching in the group of deaf individuals, highlighting the functional relevance of the observed cortical reorganization. Our results show executive processing in typically sensory regions, suggesting that the development and ultimate role of brain regions are influenced by perceptual environmental experience.

Resting-state functional connectivity in deaf and hearing individuals and its link to executive processing.

Sensory experience shapes brain structure and function, and it is likely to influence the organisation of functional networks of the brain, including those involved in cognitive processing. Here we investigated the influence of early deafness on the organisation of resting-state networks of the brain and its relation to executive processing. We compared resting-state connectivity between deaf and hearing individuals across 18 functional networks and 400 ROIs. Our results showed significant group differences in connectivity between seeds of the auditory network and most large-scale networks of the brain, in particular the somatomotor and salience/ventral attention networks. When we investigated group differences in resting-state fMRI and their link to behavioural performance in executive function tasks (working memory, inhibition and switching), differences between groups were found in the connectivity of association networks of the brain, such as the salience/ventral attention and default-mode networks. These findings indicate that sensory experience influences not only the organisation of sensory networks, but that it also has a measurable impact on the organisation of association networks supporting cognitive processing. Overall, our findings suggest that different developmental pathways and functional organisation can support executive processing in the adult brain.

Exploring Networks of Lexical Variation in Russian Sign Language.

When describing variation at the lexical level in sign languages, researchers often distinguish between phonological and lexical variants, using the following principle: if two signs differ in only one of the major phonological components (handshape, orientation, movement, location), then they are considered phonological variants, otherwise they are considered separate lexemes. We demonstrate that this principle leads to contradictions in some simple and more complex cases of variation. We argue that it is useful to visualize the relations between variants as graphs, and we describe possible networks of variants that can arise using this visualization tool. We further demonstrate that these scenarios in fact arise in the case of variation in color terms and kinship terms in Russian Sign Language (RSL), using a newly created database of lexical variation in RSL. We show that it is possible to develop a set of formal rules that can help distinguish phonological and lexical variation also in the problematic scenarios. However, we argue that it might be a mistake to dismiss the actual patterns of variant relations in order to arrive at the binary lexical vs. phonological variant opposition.

Crossmodal reorganisation in deafness: Mechanisms for functional preservation and functional change.

The study of deafness and blindness has contributed unique knowledge to our understanding of the brain, showing that environmental experience critically shapes neural structure and function. Nevertheless, the most prevalent theories of crossmodal plasticity propose opposing views about the function of reorganised cortical regions. Some theories agree on functional preservation, where in the absence of early sensory stimulation, cortical regions respond to a different sensory modality, but perform the same function. Others propose that the absence of sensory stimulation from birth results in cortical regions changing their "typical" sensory processing function to higher-order cognition. Both deafness and blindness have provided vast evidence in support of each of these theories. Here we use examples from the study of deafness to explore organisational mechanisms that would allow functional preservation and functional change to co-exist either in the same or adjacent regions. We provide a set of predictions and testable hypotheses that support each of these accounts, and lay out some steps that could move us towards more specific theories of cortical reorganisation.