CONICET | Buscador de Institutos y Recursos Humanos

Structural asymmetries of brain regions associated with lateralised functions havebeen extensively studied. However, there are fewer morphometric analyses of asymmetriesof the gyri and sulci of the entire cortex. The current study assessed corticalasymmetries in a sample of healthy adults (N = 175) from an admixed population fromSouth America. Grey matter volume and surface area of 66 gyri and sulci were quantifiedon T1 magnetic resonance images. The departure from zero of the differencesbetween left and right hemispheres (L-R),a measure of directional asymmetry (DA),the variance of L-R,and an index of fluctuating asymmetry (FA) were evaluated foreach region. Significant departures from perfect symmetry were found for most corticalgyri and sulci. Regions showed leftward asymmetry at the population level in thefrontal lobe and superior lateral parts of the parietal lobe. Rightward asymmetry wasfound in the inferior parietal, occipital, frontopolar, and orbital regions, and the cingulate(anterior, middle, and posteriorventral). Despite this general pattern, several sulcishowed the opposite DA compared to the neighbouring gyri, which remarks the needto consider the neurobiological differences in gyral and sulcal development in thestudy of structural asymmetries. The results also confirm the absence of DA in mostparts of the inferior frontal gyrus and the precentral region. This study contributeswith data on populations underrepresented in the databases used in neurosciences.Among its findings, there is agreement with previous results obtained in populationsof different ancestry and some discrepancies in the middle frontal and medial parietalregions. A significant DA not reported previously was found for the volume of longand short insular gyri and the central sulcus of the insula, frontomarginal, transversefrontopolar, paracentral, and middle and posterior parts of the cingulate gyrus andsulcus, gyrus rectus, occipital pole, and olfactory sulcus, as well as for the volume andarea of the transverse collateral sulcus and suborbital sulcus. Also, several parcelsdisplayed significant variability in the leftright differences, which can be partially attributableto developmental instability, a source of FA. Moreover, a few gyri and sulcidisplayed ideal FA with non-significant departures from perfect symmetry, such assubcentral and posterior cingulate gyri and sulci, inferior frontal and fusiform gyri, and the calcarine, transverse collateral, precentral, and orbital sulci. Overall, these resultsshow that asymmetries are ubiquitous in the cerebral cortex.

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