Concurrent Alterations in Brain Hemispheric Asymmetry of Structural and Functional Networks in Single-Sided Deafness

Brain asymmetry of structure and function, which is critical for high-level cognitive abilities, is influenced by the information received and processed in the two hemispheres. Single-sided deafness (SSD) is a prevalent clinical condition, representing an extreme case of partial sensory deprivation. However, how unilateral hearing loss affects brain hemispheric asymmetry remains poorly understood. To address this issue, we recruited 35 postlingual-onset long-term SSD patients (19/16 left/right SSD) and 18 normal hearing controls, collected their structural (diffusion tensor imaging) and resting-state functional magnetic resonance imaging data, performed deterministic fiber tractography and functional connectivity analysis to construct white matter structural and resting-state functional networks, and examined plastic alterations in their topological asymmetry across multiscale hierarchical networks (i.e., global, modular, and nodal networks). Our results revealed a rightward shift in hemispheric asymmetry for both structural and functional networks after unilateral hearing deprivation, particularly in patients with right SSD, which was related to an increase in topological properties of the right hemisphere (RH), suggesting improved connection efficiency of the RH. Moreover, in-depth modular and nodal analyses revealed that reorganized global asymmetry was driven mainly by altered asymmetry in sensory and multisensory integration areas (i.e., the temporal lobe, the occipital lobe, and subcortical nuclei). Together, these findings indicate that SSD induces concurrent reorganization in brain asymmetry of both structural and functional networks. Furthermore, these findings suggest that more efficient utilization of the nondominant RH may be an important compensatory pattern after partial sensory deprivation.