Activities and Seminars

Bernard Mazoyer. Revisiting human hemispheric specialization with neuroimaging
Date: Mar 07, 2013

What: Revisiting human hemispheric specialization with neuroimaging

Where: BCBL auditorium

Who: Bernard Mazoyer, Groupe d’Imagerie Neurofonctionnelle, UMR5296 CNRS, CEA, Université de Bordeaux, France

When: 12 noon

Hemispheric Specialization (HS) is a hemisphere-dependent relationship between a cognitive function and a set of brain structures. It includes both the hosting by a given hemisphere of specialized networks that have unique functional properties and mechanisms that enable the inter-hemispheric coordination necessary for efficient cognitive processing. Long derived from neuropsychological and behavioral observations, our knowledge of HS is currently being profoundly modified by cutting-edge neuroimaging research both on the neural implementation of HS for language and spatial attention across development, and on the analysis of interactions between brain regions within and across hemispheres. HS is supported by anatomical asymmetries of GM and WM, some of which are in place at birth. These asymmetries are more heritable than handedness, which argues against a simple single gene model for HS transmission. Functional asymmetries that support HS emerge throughout development as the result of dynamic decrease in inter-hemispheric connectivity and increase of intra-hemispheric connectivity. Maturational increase in asymmetry, observed for both RH lateralization of visuo-spatial functions and LH lateralization for language, appears essential to the development of efficient cognitive networks; its defect is associated with developmental pathologies such as dysphasia and autism. Inter-hemispheric inhibition appears as a key component of the setting up of HS organization as revealed by DCM research on motor HS and the beneficial effect of suppressive rTMS over the minor (as opposed to dominant) hemisphere on recovery of lesions of motor, language and attention networks. Recent developments in network-based connectivity analysis show that HS of cognitive functions is supported by hard-wired networks of anatomical and intrinsic connectivity and by dynamic temporal changes in homotopic areas connectivity. These new findings enlighten the fundamental role of lateralization in the large-scale architecture of the human brain, whose ontogenesis has begun to be investigated with genetic-heritability brain mapping.