Brain interhemispheric connectivity: functional and structural analysis

The aim of this thesis is to investigate whether bilateral activations occur in a callosotomised patient, and to identify possible pathways through which the exchange of information between the hemispheres takes place. The architecture of the brain is characterised by two hemispheres, left and right, which are constantly in communication with each other to allow the integration of information, necessary to perform several neural functions. This transfer of information takes place thanks to the corpus callosum (CC), a C-shaped structure of white matter and nerve pathways. The CC can be surgically severed through a procedure known as corpus callosotomy, introduced as a treatment option for epilepsy. Despite the various consequences and functional effects of callosal sectioning, patients underwent callosotomy provide a useful opportunity of research, as they constitute a good neuroanatomical model for understanding human neuroplasticity and the relationship between structural and functional connectivity. Structural connectivity represents the physical anatomical connections between different groups of neurons, while functional connectivity is defined as the temporal dependency of neuronal activation patterns of anatomically separated brain regions. This study is based on the analysis of data obtained from a healthy subject and a pathological one, underwent callosotomy about 20 years before. To perform structural and functional analysis of data, Brain Voyager, a powerful neuroimaging software package for data management and data analysis, was employed. In the analysis process, the evaluation of interhemispheric functional connectivity and the recognition of the resting state networks (RSNs) were performed by using the independent component analysis technique. Afterwards, the tractography was performed and the resulted white matter tracts, connecting the region of interests defined on the individuated RSNs, were reconstructed. White matter tracts constitute the structural highways of the brain, enabling information to travel quickly from one brain region to another. The tractography was performed taking into consideration three RSNs for the healthy subject and three RSNs for the patient. Tractography results have demonstrated, for the subject, the presence of anatomical callosal fibres connecting the functionally linked activated cortical areas. For the patient, the persistence in some cases of bilateral activation would suggest the presence of subcortical pathways alternative to the CC.