Hemispheric co-lateralization of language and spatial attention reduces performance in dual-task.

Hemispheric specialization of different functions is proposed to confer evolutionary benefits, yet the behavioral impacts of lateralization and its cognitive and neural mechanisms remain unclear. This study investigated the effect of lateralization pattern between language and spatial attention on dual-task performance and its association with callosal connectivity. Functional lateralization was assessed using fMRI verbal fluency and landmark tasks, and interhemispheric connections were evaluated through diffusion-weighted imaging. The typical lateralization pattern enhanced overall performance and reduced interference in dual-task compared to the co-lateralized pattern (both functions lateralized to one hemisphere). However, no differences were observed between the mirrored pattern (right language dominance and left attention dominance) and the co-lateralized pattern. While callosal connectivity did not significantly differ among groups, a negative correlation was observed between the lateralization degree and callosal connectivity. Our findings partially support the functional crowding hypothesis and offer insights into neurocognitive mechanisms underlying functional reorganization after brain lesions.