Independent Lateralization of Language, Attention, and Numerical Cognition Across Task and Rest

Hemispheric functional complementarity is a core organizational principle of the human brain, yet the extent to which lateralization in one domain constrains that of others remains unclear. Two main accounts have been proposed: the causal hypothesis, in which dominance for one function drives complementary dominance in another, and the statistical hypothesis, in which each function lateralizes independently. Using multimodal fMRI in 287 participants from the BIL&GIN cohort, we examined whether language lateralization phenotypes, defined as typical (left-dominant) or atypical (right-dominant), predict hemispheric asymmetries in visuospatial attention and numerical cognition. Task-based activation was measured during line bisection, mental calculation, and numerical interval comparison, and analyzed within domain-specific, functionally defined network atlases. Resting-state functional connectivity metrics were also assessed in the same networks. Across both attention and numerical domains, typical individuals for language showed stronger asymmetries, whereas atypical individuals exhibited weaker, more bilateral patterns. Critically, atypical participants did not show mirror-reversed asymmetries, and language phenotype did not influence intrinsic connectivity metrics in non-language networks. These findings challenge the notion that atypical lateralization represents an inversion of the canonical template and argue against a universal reciprocal link between language dominance and other cognitive domains. Instead, our results support a domain-specific model in which lateralization profiles are shaped by distinct developmental and functional constraints, highlighting the need for multimodal, multi-domain approaches to brain asymmetry.