Topologically Reorganized Connectivity Architecture of Default-Mode, Executive-Control, and Salience Networks across Working Memory Task Loads

Abstract

The human brain is topologically organized into a set of spatially distributed, functionally specific networks. Of these networks, the default-mode network (DMN), executive-control network (ECN), and salience network (SN) have received the most attention recently for their vital roles in cognitive functions. However, very little is known about whether and how the interactions within and between these 3 networks would be modulated by cognitive demands. Here, we employed graph-based modularity analysis to identify the DMN, ECN, and SN during an N-back working memory (WM) task and further investigated the modulation of intra- and inter-network interactions at different cognitive loads. As the task load elevated, functional connectivity decreased within the DMN while increased within the ECN, and the SN connected more with both the DMN and ECN. Within-network connectivity of the ventral and dorsal posterior cingulate cortex was differentially modulated by cognitive load. Further, the superior parietal regions in the ECN showed increased internetwork connections at higher WM loads, and these increases correlated positively with WM task performance. Together, these findings advance our understanding of dynamic integrations of specialized brain systems in response to cognitive demands and may serve as a baseline for assessing potential disruptions of these interactions in pathological conditions.

The Segregation and Integration of Distinct Brain Networks and Their Relationship to Cognition

“…Although most studies examining connectivity during motorrelated tasks focus on within-network organization (Biswal et al, 1995;Jiang et al, 2004;Rissman et al, 2004;Sun et al, 2004Sun et al, , 2007Zhuang et al, 2005;Bardouille and Boe, 2012), many studies probing working memory focus on internetwork integration. Our findings are consistent with previous studies demonstrating increased integration during tasks presumed to tap working memory with increasing load or compared to rest (Kitzbichler et al, 2011;Gordon et al, 2012;Cohen et al, 2014;Liang et al, 2016) and that increased integration is related to increased behavioral performance (Bassett et al, 2009;Cohen et al, 2014;Stanley et al, 2014;Braun et al, 2015). We extend this literature by using several measures of segregation and integration to provide convergent evidence for increased integration during working memory.…”

Large‐scale brain networks are distinctly affected in right and left mesial temporal lobe epilepsy

“…The relationship between DMN, salience and ECNs is under investigation, but recent studies defined that DMN and salience work oppositely, meaning that the increase of the first is followed by a decrease in the second, and vice‐versa [Balthazar, et al, 2014]. Some authors suggest that this mechanism involves a mediation of activity executed by the salience network guiding the focus on internal (DMN) or external (ECN) process and stimulus [Liang et al, 2016]. …”

Intrinsic Functional Connectivity Patterns Predict Consciousness Level and Recovery Outcome in Acquired Brain Injury

“…The rotational displacements were converted from radians to millimeters by calculating the displacement on the surface of a sphere of radius 50 mm Liang et al, 2013). To moderate the effects of head motion on estimates of functional connectivity, we censored volumes within each participant's restingstate fMRI time series that were associated with sudden head motion (i.e., the volumes with FD i Ͼ0.5 mm).…”

“…Resting-state fMRI studies have demonstrated that hubs in the brain, which have high functional connectivity strength (FCS) and high rates of cerebral blood flow and glucose metabolism (Liang et al, 2013;Tomasi et al, 2013), serve to integrate diverse information sources (Achard et al, 2006;Buckner et al, 2009;Bullmore and Sporns, 2009;He and Evans, 2010;van den Heuvel and Sporns, 2013). These brain hubs are predominantly located in regions of the default mode network (DMN), including the posterior cingulate cortex (PCC)/precuneus (PCU), the medial prefrontal cortex, and the lateral temporal and parietal cortices (Raichle et al, 2001).…”

“…Several small-sample, resting-state fMRI studies using seedbased functional connectivity and independent component analysis have consistently shown that patients with acquired brain injury experience disrupted functional connectivity in the DMN, mainly in the PCC/PCU (Boly et al, 2009;Norton et al, 2012), a major hub node of the brain. Recently, another small-sample, resting-state fMRI study based on graph theory showed functional reorganization of hub regions in coma patients; cortical regions (e.g., PCU) that were major hubs of healthy brain networks had typically become non-hubs in comatose brain networks (Achard et al, 2012).…”