Functional language lateralization during sentence completion in the healthy brain is not associated with the...

Familial sinistrality (left-handedness) has been suggested as a proxy for functional language lateralization in the healthy adult brain. Previous studies show that individuals with familial sinistrality tend to have less lateralized language-related brain activation, while individuals without familial sinistrality show greater left-hemispheric lateralization for language. However, familial sinistrality trait has always been treated as a binary categorical variable. In this study a more sensitive quantitative estimate of familial sinistrality (LH load) has been modelled in 39 participants with different direction and degree of handedness by applying a standard genetic multifactorial model. This LH load was tested for an association with functional language lateralization based on an fMRI sentence completion task. Using frequentist and Bayesian statistical frameworks, the association between LH load and language lateralization was not confirmed. The findings of the present research suggest that a quantitative measure of familial sinistrality is not related to individual language representation in the brain measured by a sentence completion fMRI paradigm. However, considering the context of our study and previous research we suggest that familial sinistrality being related to personal handedness could drive functional language lateralization through it.