Functional connectivity in neuroinflammatory conditions

Neuroinflammatory conditions are diseases characterized by the direct inflammation of the central nervous system (CNS). Several neurological disorders have a neuroinflammatory substrate, including multiple sclerosis (MS), which is probably the most frequent, as well as neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD). Many systemic immune-mediated diseases, such as neuropsychiatric systemic lupus erythematosus (NP-SLE), can also involve the CNS. Functional connectivity (FC) is a useful technique that allows investigating how different brain regions interact for efficient brain function. This is achieved by analyzing sets of brain regions, voxelwise connections, or entire brain networks. In principle, FC analysis can be performed on task-based fMRI scans; however, the large majority of FC studies are carried out on resting state (RS) fMRI data because of their easier standardization and wide applicability. In this chapter, we give an overview of the main results obtained by resting-state functional connectivity (RS FC) studies in neuroinflammatory conditions. The largest portion of the chapter is dedicated to MS and reviews the most important findings in this condition (including reorganization of functional systems in relation to patients' clinical and cognitive features, complex network dysfunction, and longitudinal and time-varying connectivity). Then, the principal RS FC results in other neuroinflammatory conditions, including NMOSD, MOGAD, and NP-SLE, are illustrated.