It has long been proposed that structural cortical asymmetries may underlie functional lateralization of the human brain. Given that interhemispheric differences in language processing are one of the most pronounced, most studies investigated whether this functional asymmetry has a structural correlate. Recently, it has been demonstrated that it is the insular cortex asymmetry (not the Broca’s area or planum temporale) that is linked to the lateralization of verbal fluency in right-handers. Whether or not this effect can be seen in left-handers is unknown. Moreover, language and gesture representations are co-lateralized. Therefore, if common cortical asymmetries underlie both of these functions then the structure of the insular cortex could also determine them both. Finally, given that gestures are supported by a distributed praxis representation network involving parieto-frontal pathways, other asymmetries may also contribute to the lateralization of this function. Here, we demonstrate that despite the existence of significant asymmetries observed in the superior parietal lobes, only the inter-hemispheric differences in the insular cortex are related to gesture lateralization. Moreover, this study shows that even in left-handed individuals language representation is reflected in insular asymmetry. In sum, the structure of the insula may be paramount to cerebral specialization for both gestures and language.
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