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Brain compensatory mechanisms and cognition in early multiple sclerosis
B. Audoin
Aix-Marseille Université, CNRS, CRMBM UMR 7339, APHM, Pôle de Neurosciences Cliniques, Marseille, France
Cognitive impairment is present from the very first stage of multiple sclerosis and is mainly characterized by deficits of speed of information processing, attention and executive functioning. At the early stage of the disease, cognitive impairment appears mainly underline by long distance connectivity disturbances secondary to early diffuse brain white matter damage. These structural damages may induce significant changes in the functional organization of the brain that may be related to adaptive or maladaptive reorganizations. Functional MRI studies have brought new insight into the better understanding of brain reorganization reactive to multiple sclerosis injury. First, task related fMRI studies demonstrated that patients at the early stage of the disease performing complex cognitive tasks showed higher activation in high level cortical regions included in the fronto-parietal network. In these regions, higher activation was associated with higher brain tissue damage but also with lower cognitive performances suggesting the existence of maladaptive or partially adaptive compensatory mechanisms. Recently, resting-state fMRI studies have provided new findings evidencing that connectivity strength was higher in the majority of brain cognitive networks in patients at the first stage of the disease. In addition, higher cognitive deficit were correlated with higher connectivity strength in the cognitive neuronal networks. Graph theoretical approach of resting state fMRI data evidenced that the modularity of the brain was increased at this stage of the disease especially in patients with cognitive impairment. These recent findings suggest that brain functional reorganization occurring in patients at the early stage of the disease is characterized by connectivity disturbances between brain specialized sub-networks increasing the modularity of the brain and a reactive enhancement of the connectivity strength into these sub-networks related to partially compensatory mechanisms. Reorganization into these sub-networks may be especially located in hub regions particularly involved in the connectivity between sub-networks.
Brain compensatory mechanisms and cognition in early multiple sclerosis
B. Audoin
Aix-Marseille Université, CNRS, CRMBM UMR 7339, APHM, Pôle de Neurosciences Cliniques, Marseille, France
Cognitive impairment is present from the very first stage of multiple sclerosis and is mainly characterized by deficits of speed of information processing, attention and executive functioning. At the early stage of the disease, cognitive impairment appears mainly underline by long distance connectivity disturbances secondary to early diffuse brain white matter damage. These structural damages may induce significant changes in the functional organization of the brain that may be related to adaptive or maladaptive reorganizations. Functional MRI studies have brought new insight into the better understanding of brain reorganization reactive to multiple sclerosis injury. First, task related fMRI studies demonstrated that patients at the early stage of the disease performing complex cognitive tasks showed higher activation in high level cortical regions included in the fronto-parietal network. In these regions, higher activation was associated with higher brain tissue damage but also with lower cognitive performances suggesting the existence of maladaptive or partially adaptive compensatory mechanisms. Recently, resting-state fMRI studies have provided new findings evidencing that connectivity strength was higher in the majority of brain cognitive networks in patients at the first stage of the disease. In addition, higher cognitive deficit were correlated with higher connectivity strength in the cognitive neuronal networks. Graph theoretical approach of resting state fMRI data evidenced that the modularity of the brain was increased at this stage of the disease especially in patients with cognitive impairment. These recent findings suggest that brain functional reorganization occurring in patients at the early stage of the disease is characterized by connectivity disturbances between brain specialized sub-networks increasing the modularity of the brain and a reactive enhancement of the connectivity strength into these sub-networks related to partially compensatory mechanisms. Reorganization into these sub-networks may be especially located in hub regions particularly involved in the connectivity between sub-networks.
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