Abstract
The control of gesture is one of the most left-lateralized functions, and the insular cortex is one of the most left-biased structures in the human brain. Therefore, we investigated whether structural asymmetries of the insula are linked to the organization of functional activity during gesture planning. We reconstructed and parcellated the insular cortex of 27 participants. First, we tested 15 strongly left-handed individuals because of a higher incidence of atypical organization of functions such as gesture and language in such a population. The inter-hemispheric structural asymmetries were compared with the lateralization of activity for gesture in the supramarginal gyrus (the hotspot of signal increase regardless of the gesturing hand) and Broca’s area (the hotspot of signal increase for language production). The more pronounced leftward structural asymmetries were accompanied by greater left-hemisphere dominance for both of the studied functions. Conversely, an atypical, bilateral or rightward functional shift of gesture and language was accompanied by an attenuated leftward asymmetry of the insula. These significant relationships were driven primarily by differences in surface area. Subsequently, by adding 12 right-handed individuals to these analyses we demonstrated that the observed significant associations are generalizable to the population. These results provide the first demonstration of the relationships between structural inter-hemispheric differences of the insula and the cerebral specialization for gesture. They also corroborate the link between insular asymmetries and language lateralization. As such, these outcomes are relevant to the common cerebral specialization for gesture and language.
Highlights
One of the most intriguing characteristics of the human brain is lateralization of its functions
We found no evidence of any asymmetries for cortical thickness in any region of interest (ROI) considered
Consistently with the ROI analyses, at a group level analysis we did find clusters of significant leftward surface asymmetries located within the insular cortex, but not in the planum temporale
Summary
One of the most intriguing characteristics of the human brain is lateralization of its functions. Despite great strides that have been made, our understanding of the causes behind these functional asymmetries remains limited (Toga & Thompson, 2003). It has been suggested, for example, that anatomical differences between the two cerebral hemispheres could reflect or even determine functional lateralization (Geschwind & Galaburda, 1985). No clear-cut evidence for associations between the structural hemispheric differences of these regions and language lateralization were shown (Keller et al, 2009; cf Josse et al, 2009). The absence [The copyright line was updated on 23 July 2015, after original online publication.]
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