Heschl’s gyrus anatomy and hemispheric specialization : a study in a database of 430 healthy volunteers

décembre 2013

Directeur(s) de thèse : Nathalie TZOURIO-MAZOYER

Résumé de thèse

This thesis concerned the macroscopical anatomy of Heschl’s gyri (HG) in relation with Manual Preference (MP) and the Hemispheric Specialization for Language (HSL) studied in a multimodal database dedicated to the investigation of HS and balanced for sex and MP (BIL&GIN). HG, located on the surface of the temporal lobe, hosts the primary auditory cortex. Previous studies have shown that HG volume is leftward asymmetrical and that the left HG (LHG) covaries with phonological performance and with the amount of cortex dedicated to the processing of the temporal aspects of sounds, suggesting a relationship between LHG and HSL. However HG anatomy is highly variable and little known. In this thesis we have: 1- Described HG inter-hemispheric gyrification pattern on the anatomical MRI images of 430 healthy participants belonging to the BIL&GIN. 2- Studied the variation of the first or anterior HG (aHG) surface area and its asymmetry and shown its reduction in the presence of duplication, plus that its leftward asymmetry was present only in the case of a single LHG. Left-handers exhibited a lower incidence of right duplication and a loss of aHG leftward asymmetry. 3-Tested whether the variance of HG anatomy explained the interindividual variability of asymmetries measured with fMRI during the listening of a list of words in 281 participants, and whether differences in HG anatomy with MP were related to decreased HSL in left-handers. HG inter-hemispheric gyrification pattern explained 11% of the variance of HG functional asymmetry, the patterns including a unique LHG being those with the strongest leftward asymmetry. There was no incidence of MP on HG functional lateralization.