Hemisphere and Gender Differences in the Rich-Club Organization of Structural Networks.

Structural and functional differences in brain hemispheric asymmetry have been well documented between female and male adults. However, potential differences in the connectivity patterns of the rich-club organization of hemispheric structural networks in females and males remain to be determined. In this study, diffusion tensor imaging was used to construct hemispheric structural networks in healthy subjects, and graph theoretical analysis approaches were applied to quantify hemisphere and gender differences in rich-club organization. The results showed that rich-club organization was consistently observed in both hemispheres of female and male adults. Moreover, a reduced level of connectivity was found in the left hemisphere. Notably, rightward asymmetries were mainly observed in feeder and local connections among one hub region and peripheral regions, many of which are implicated in visual processing and spatial attention functions. Additionally, significant gender differences were revealed in the rich-club, feeder, and local connections in rich-club organization. These gender-related hub and peripheral regions are involved in emotional, sensory, and cognitive control functions. The topological changes in rich-club organization provide novel insight into the hemisphere and gender effects on white matter connections and underlie a potential network mechanism of hemisphere- and gender-based differences in visual processing, spatial attention and cognitive control.

Dynamic reconfiguration of functional brain networks supporting response inhibition in a stop-signal task.

Response inhibition is the ability to suppress automatic actions or behaviors that are not appropriate or are no longer adaptive to the situation. Although many studies have suggested regional brain activation, the nature of the reconfiguration of functional brain networks involved in response inhibition remains unknown. Here, we assessed brain changes associated with response inhibition using graph theoretical analysis applied to functional connectivity data acquired while subjects performed a simple stop-signal task. We identified several ways in which global network organization shifted to meet the demand for response inhibition. Increased demand for response inhibition was associated with a global network configuration with more efficient communication across the network (functional integration) and more specialized processing (functional segregation). Regions distributed in the frontoparietal network and attention networks were found to be highly efficient in the stop condition. Nodal efficiency was significantly associated with reaction time and showed a different pattern between the go and stop conditions. In addition, the conditional differences (stop vs. go) in nodal efficiency and regional task activation were common in the postcentral gyrus (PoCG) and superior temporal lobe gyrus (STG), and a negative correlation between these differences was found in the frontal and parietal lobes. These results provide compelling evidence that response inhibition is associated with truly global changes in brain functional connectivity and additional insights into how defects in response inhibition are associated with neurological or psychiatric difficulties.