PD23-01\u2003SMALL-WORLD BRAIN NETWORK TOPOLOGY IN WOMEN WITH AND WITHOUT OVERACTIVE BLADDER

Abstract

INTRODUCTION AND OBJECTIVES: The recently emerging field of network neuroscience provides new opportunities to investigate network topology of the whole brain organization; however, the brain network topology in micturition states has not been measured. Accumulating evidence suggests that the human brain can be characterized as a small-world network which is optimally organized for efficient information integration. Previous neuroimaging studies have shown that overactive bladder (OAB) is associated with functional abnormalities in specific brain regions; however, the extent to which brain network topology is altered by OAB remains unknown. The aim of this study is to use functional magnetic resonance imaging (fMRI) to explore brain small-world network changes during bladder filling in women with OAB as well as in healthy controls. To our knowledge, this is the first study to apply the concepts of small-world brain network topology to micturition. METHODS: Eleven women with OAB and 11 healthy controls were scanned in a Siemens 3T scanner in a low urgency state (empty bladder) after voiding and a high urgency state after drinking oral fluids. Urinary urgency ratings (scale 0-10) were obtained before and after each scan. Using GRETNA toolbox, graph theoretical analysis was conducted on fMRI data to calculate brain small-world network metrics, including the ratio for the clustering coefficients between the real and random network (Gamma), and the ratio for the characteristic path length between the real and random network (Lambda), and the network small-worldness (Sigma), and examine the relationships between these network properties and urgency scores. RESULTS: The brain networks of OAB patients and healthy controls all clearly demonstrate the features of small-world network by having a clustering coefficient higher than a random network (Gamma > 1), and a characteristic path-length similar to a random graph (Lambda ≈ 1). Comparisons between small-world network metrics between low and high urgency conditions did not show significant differences in OAB patients or controls. However, OAB patients showed significantly reduced Lambda than controls during the low urgency state (P<0.05) but not the high urgency state (P>0.5). Moreover, increase in urgency scores in the OAB group was negatively correlated with a change in the Lambda (r=-0.706, P=0.015) and positively correlated with a change in the Gamma (r=0.680, P=0.021) and a change in network small-worldness (Sigma, r=0.825, P=0.002). No such correlations were found between urinary urgency scores and brain small-world properties in the control group. CONCLUSIONS: Bladder filling is associated with changes in the brain small-world network organization metrics in women with OAB but not in controls. OAB patients also showed reduced characteristic path-length than controls. These findings suggest that urinary urgency in OAB may represent a disruption of whole-brain functional network topology in addition to regional brain activity changes. Future development of OAB treatments may need to target not only specific regions of the brain but also how information is integrated across the full brain network. Source of Funding: None