Altered excitation-inhibition balance in the somatomotor and default mode network in multiple sclerosis

IntroductionThe balance between excitatory and inhibitory (E/I) neural processes is a fundamental principle of brain function, and its disruption has been implicated in the pathophysiology of multiple sclerosis (MS). In vivo assessment of E/I balance has traditionally relied on electrophysiological measures, and despite the abundance of fMRI data on MS, no fMRI-based technique has so far been presented to measure E/I balance in MS. MethodsRecently, a novel MRI-based method has been introduced to estimate E/I balance by integrating functional MRI and diffusion weighted imaging data. We use this approach to study E/I balance in MS at a global (over the whole head) and at the local level of specific resting state networks affected by MS: the somatomotor and Default Mode network (DMN). Furthermore, we perform the analysis using three different atlases: the Schaefer atlas, which is functionally defined, and the Automatic Anatomical Labeling (AAL) and Desikan Killany (DK) atlas, which are defined based on structural features. ResultsOur findings reveal a significant alteration in E/I balance within the somatomotor and default mode networks when using the functionally defined Schaefer atlas, suggesting a network-specific dysfunction in MS. We also find that the E/I balance inferred within the somatomotor network correlates with motor fatigue. ConclusionsThis study demonstrates a promising framework for investigating E/I balance alterations in neurological disorders and paves the way for validation in larger cohorts.