Associations between fMRI signal amplitude, hemispheric asymmetry, and task performance.

Interhemispheric asymmetry is a core feature of human brain organization, yet its functional relevance across cognitive tasks remains incompletely understood. Using data from 989 healthy adults, we examined patterns of functional asymmetry and their relationship to bilateral fMRI signal amplitude and task performance across seven tasks: motor, language, social cognition, relational processing, working memory, gambling, and emotion. An fMRI-derived asymmetry index was computed across 17 task epochs and mapped onto the cortical surface. Here we show that both fMRI signal amplitude and asymmetry were positively associated with task accuracy across multiple networks and tasks epochs. These associations were strongest in language, frontoparietal, and dorsal attention networks during high-demand tasks, such as story comprehension, relational processing, and working memory. Partial least squares regression revealed that amplitude was a more robust predictor of task accuracy than asymmetry. These findings suggest that greater neural activation drives stronger hemispheric differentiation and supports cognitive performance.