Background: In multiple sclerosis (MS), relationships between disease-related MRI changes, cognitive function and brain responses are complex and still unclear. This study addresses the relative effects of cognitive impairment and brain atrophy on the cortical reorganization associated with a visuo-motor task.
Methods: Multivariate analysis was applied to compare functional MRI brain responses of 28 relapsing-remitting (RR) MS patients (16 cognitively preserved and 12 cognitively impaired) to that of 35 matched healthy controls during the execution of visuo-motor integration task. Regression analysis was performed to test for linear effects of structural variables (grey matter (GM) and white matter (WM) volumes) and cognitive profiles--and their combined effect--on the same response.
Results: Compared to preserved MS patients or normal controls, cognitively impaired MS patients showed significant decreases of brain parenchymal and GM volumes, but only a trend for lower WM volume. Multivariate analysis showed that cognitive profile, GM and WM atrophy independently contributed to the activation of parieto-premotor cortices. Baseline cognition predicted the greatest response of the entire network, whereas WM and GM losses predicted selective responses of parietal and premotor regions.
Conclusions: Visuo-motor function in MS is associated with altered patterns of brain activation that vary as a function of cognitive decline. This is confirmed by a larger effect size of the individual cognitive profile compared to the structural damage. Both effects contribute in an additive way to cortical reorganization, which is primarily driven by such a cognitive gradient in RR-MS patients.