Structural constraints of functional connectivity drive cognitive impairment in the early stages of multiple
Ismail Koubiyr1, Mathilde Deloire2, Bruno Brochet3
1University of Bordeaux, Bordeaux, France; Inserm U1215 - Neurocentre Magendie, Bordeaux, France.
Background:
The relationship between structural and functional deficits in multiple sclerosis (MS) is unclear.
Objective:
This study explored structure-function relationships during the 5 years following a clinically isolated syndrome and their role in cognitive performance.
Methods:
Thirty-two patients were enrolled after their first neurological episode suggestive of MS and followed for 5 years, along with 10 matched healthy controls. We assessed structural (using diffusion tensor imaging) and functional (using resting-state functional magnetic resonance imaging (fMRI)) brain network metrics, clinical and cognitive scores at each follow-up visit. Structural-functional coupling, calculated as the correlation coefficient between strengths of structural and functional networks, was used to assess structure-function relationships.
Results:
Structural clustering coefficient was significantly increased after 5 years, whereas characteristic path length decreased. Structural connections decreased after 1 year and increased after 5 years. Functional connections and related path lengths were decreased after 5 years. Structural-functional coupling had increased significantly after 5 years. This structural-functional coupling was associated with cognitive and clinical evolution, with stronger coupling associated with a decline in both domains.
Conclusion:
Our findings provide novel biological evidence that MS leads to a more constrained anatomical-dependant functional connectivity. The collapse of this network seems to lead to both cognitive worsening and clinical disability.
