Hemispheric Complementarity is Associated with Distinct Functional and Structural Brain Profiles

The concept of hemispheric complementarity - the idea that brain functions are specialized to different sides of the brain - has long been a topic of study. However, its consistency across individuals and its impact on cognition have been subjects of debate. Researchers have now used multimodal neuroimaging and twin-family data from 987 participants of the Human Connectome Project to shed light on this matter.

The study identified three distinct attentional lateralization phenotypes - right, left, and bilateral - that were independent of handedness. These phenotypes differed by sex and tracked significant shifts in brain organization. Bilateral individuals showed stronger intrahemispheric and homotopic connectivity, while right and left individuals exhibited stronger lateralized connectivity.

Further analysis revealed three multidomain profiles related to attention and language: crowded, mixed, and split. These profiles indicated whether functions were localized within one hemisphere or distributed across both. The mixed organization was linked to higher myelination in the planum polare, a region associated with early language processing.

On the other hand, crowded organization showed higher fiber density connectivity across the dorsal attention-default network, a network involved in orienting attention and monitoring the environment.

Both phenotypes were found to be heritable, meaning they can be passed down through generations. However, neither phenotype predicted cognitive performance. This suggests that while brain organization is influenced by genetic factors, it does not necessarily determine cognitive abilities.

In conclusion, the study reveals a brain organization where specialization emerges from flexible, heritable patterns. These patterns link function, structural connectivity, and myeloarchitecture - the organization of white matter fibers in the brain. This finding challenges the traditional view of strict hemispheric specialization and instead proposes a more nuanced model of brain organization.