Electroencephalography-derived functional connectivity in sensorimotor networks in Stroke and Multiple Sclerosis Fatigue

A common mechanism of altered sensory processing is the basis of chronic fatigue in neurological disorders. Here we test the hypothesis Altered connectivity in sensory networks underlies chronic fatigue in stroke and multiple sclerosis. In 46 non-depressed, minimally impaired stroke survivors (n=29) and multiple sclerosis patients (n=17), median disease duration of 5 years, resting state neuronal activity was measured using 64-channel electroencephalography. Graph theory-based network analysis measure of functional connectivity (small-world index) was calculated in right and left motor (Brodmann areas 4, 6, 8, 9, 24 and 32) and somatosensory (Brodmann areas 1, 2, 3, 5, 7, 40 and 43) networks, in 5 frequency bands: delta, theta, alpha, beta and gamma. Fatigue was measured using Fatigue Severity Scale (Stroke) and modified Fatigue Impact Scale (MS), with scores of >4 (FSS) and >38 (mFIS), defined as high fatigue. Both stroke survivors and multiple sclerosis patients with high fatigue showed significantly more small-worldness in the right sensory networks in the beta band frequency. Additionally, only in stroke survivors with high fatigue, there was decreased small-worldness in the left motor network in the delta and theta bands. Altered sensory network connectivity is common to both stroke and MS fatigue, indicating impaired sensory processing as a disease-independent mechanism of chronic fatigue in neurological conditions. Furthermore, such difference in functional connectivity emerges in beta band activity, further strengthening the idea of altered sensorimotor processing as the basis of chronic neurological fatigue.