Increased functional brain network modularity predicts working memory deficits in early-stage multiple sclerosis

Multiple sclerosis is a neurological disorder where, due to inflammatory processes, there is focal demyelination and axonal damage that step-by-step severs the anatomical connections of the brain. Recent neuroimaging studies and theoretical work are both pointing out the importance of inter-area connectivity and interactions in giving rise to perceptual and cognitive functions. Therefore, one of the crucial questions regarding multiple sclerosis is in which ways the breaking down of brain connectivity alters the way that the functional networks are reorganized and how this impacts cognition.

In their recent study, Gamboa et al. (2013) recorded resting state functional magnetic resonance imaging in early-stage multiple sclerosis patients and healthy controls. As a measure of cognition, subjects of both groups separately performed the Paced auditory serial addition task in a dual task manner to assess working memory, attention, and speed of information processing. Using graph theoretical analysis of brain functional connectivity, the authors observed increased modularity in the early-stage multiple sclerosis patients as compared with the healthy controls. Furthermore, the increased modularity of brain functional connectivity negatively correlated with performance in the neuropsychological test of working memory, attention, and speed of information processing.

These highly interesting findings demonstrate how the subtle changes in connectivity due to focal damage caused to axonal fibers in the earliest stages of multiple sclerosis alter the functional network properties of the brain, and how such changes in brain network activity adversely reflects upon cognitive ability. It is easy to see how these findings pave way for further studies examining how accumulating focal damage to the links of the functional networks affect perceptual and cognitive functions in multiple sclerosis patients. Given that relatively robust effects were seen in these early-stage patients, these findings could also be interesting from the point of view of clinical research aiming at development of measures that enable follow-up of disease progression.

Reference: Gamboa OL, Tagliazucchi E, vonWegner F, Jurcoane A, Wahl M, Laufs H, Ziemann U. Working memory performance of early MS patients correlates inversely with modularity increases in resting state functional connectivity networks. NeuroImage (2013) e-publication ahead of print. http://dx.doi.org/10.1016/j.neuroimage.2013.12.008