Surface-based characterization of healthy human adult cortex: An investigation of its morphological variability, late maturation and asymmetriesseptembre 2016 Directeur(s) de thèse : Fabrice Crivello Résumé de thèse
Recent in vivo neuroimaging techniques allow to investigate the complexity of the human brain anatomy by the quantification of multimodal and multiscale microstructural features. In the present thesis, we applied such up to date automated surface-based brain image analysis software to extract structural phenotypes of the healthy human cerebral cortex, namely the cortical thickness, the surface area, the sulcal depth, the curvature and the intracortical myelin content. The principal aim of this work was to characterize those multimodal structural variables in a large database of 450 healthy adults aged from 18 to 57 years (BIL&GIN database) in order to describe comprehensively the inter-individual variability of brain structural organization and notably to search for anatomical markers of brain maturation and lateralization.
We first applied this methodology to Heschl’s gyrus, hosting the primary auditory cortex, and having high macroscopical variability due to variation in its gyrification pattern. We showed that the partial or complete duplication of the Heschl’s gyrus was associated to loco-regional modifications in terms of cortical thickness, surface area and intra-cortical myelination located posteriorly to this gyrus and in the planum temporale, two regions being implied in language processing.
In a second study, we investigated the cortical structural modifications associated to late maturation (between 18 and 30 years-old) and cortical atrophy associated with aging (after 30 years-old). We defined a maturation index based on an integration of cortical thickness and intracortical myelin that allowed the discrimination of two different patterns of anatomical changes of the cerebral cortex during these different stages of life.
Finally, we characterized cortical asymmetries using a specific hemispheric surface-matching which removes differences in sulcal morphology and position between hemispheres. This approach allowed us to highlight regions where asymmetries of thickness and surface area were concordant (leftward or rightward asymmetry for both variables) and regions of opposite asymmetries (leftward for one and rightward for the other). 20% of regions that showed overlap of cortical thickness and surface area significant asymmetries presented negative correlation between these variables. On the opposite, the two cortical areas with the strongest anatomical asymmetries in Humans – leftward for the planum temporale and rightward for the superior temporal sulcus – exhibited positive correlations between CT and CSA asymmetries. These areas are key sites for the understanding of anatomical asymmetries in Humans calling for further investigations of their relevance as markers of functional brain lateralization within the frame of the search for the origins of hemispheric specialization.
Keywords: neuroimaging, human brain anatomy, interindividual variability, Heschl’s gyrus, maturation, asymmetry, surface-based morphometry.