Default Mode Network Connectivity Changes Research Articles

Aberrant Default-Mode Functional Connectivity in Patients with End-Stage Renal Disease: A Resting-State Functional MR Imaging Study

To investigate the functional connectivity of the default-mode network (DMN) in patients with end-stage renal disease (ESRD) by using independent component analysis of resting-state functional magnetic resonance (MR) imaging and to correlate these DMN connectivity changes with neuropsychological test results and clinical biomarkers. Medical research ethics committee approval and written informed consent were obtained. Forty-six patients with ESRD, including 22 with minimal nephrotic encephalopathy (MNE) and 24 without nephrotic encephalopathy, and 23 healthy control subjects underwent resting-state functional MR imaging. All patients were asymptomatic and without history of neurologic or psychiatric disease. Independent component analysis was used to isolate the DMN. To display the voxels that contributed most strongly to an independent component, the intensity values in each spatial map were converted to z scores, which indirectly provided a measurement of functional connectivity in the DMN. Maps of the DMN were compared among the groups. Pearson correlation analysis was performed to correlate abnormal DMN functional connectivity with serum urea, creatinine, duration of dialysis, duration of disease, and neuropsychological test scores. Patients with ESRD showed significantly less functional connectivity in the posterior cingulate cortex, precuneus, and medial prefrontal cortex (MPFC) (P < .01) than did control subjects. Comparison of the two patient groups showed significantly reduced functional connectivity in the superior and MPFC in the MNE group (P < .01). The functional connectivity of the MPFC was positively correlated with digital symbol test score (R = 0.293, P = .048). Serum creatinine level was negatively correlated with functional connectivity of the posterior cingulate cortex and precuneus in patients with ESRD (R = -0.51, P = .002). Functional connectivity in the DMN was impaired in patients with ESRD, with further reduction in the MPFC with the development of MNE, which might explain the reduced performance of these patients on neurocognitive tests. Serum creatinine level might be associated with impairment of the DMN in patients with ESRD.

A preliminary study on the effects of acute ethanol ingestion on default mode network and temporal fractal properties of the brain

To study the effect of acute alcohol intoxication on the functional connectivity of the default mode network (DMN) and temporal fractal properties of the healthy adult brain. Eleven healthy male volunteers were asked to drink 0.59 g/kg of ethanol. Resting state blood oxygen level dependent (rsBOLD) MRI scans were obtained before consumption, 60 min post-consumption and 90 min post-consumption. Before each rsBOLD scan, pointed-resolved spectroscopy (PRESS) (1)H-MRS (magnetic resonance spectroscopy) scans were acquired to measure ethanol levels in the right basal ganglia. Significant changes in DMN connectivity were found following alcohol consumption (p < 0.01). Both increased and decreased regional connectivity were found after 60 min, whereas mostly decreased connectivity was found after 90 min. The fractal behaviour of the rsBOLD signal, which is believed to help reveal complexity of small-scale neuronal circuitry, became more ordered after both 60 and 90 min of alcohol consumption (p < 0.01). The DMN has been linked to personal identity and social behavior. As such, our preliminary findings may provide insight into the neuro-functional underpinnings of the cognitive and behavioral changes observed during acute alcohol intoxication. The reduced fractal dimension implies a change in function of small-scale neural networks towards less complex signaling.

Default-Mode Network Disruption in Mild Traumatic Brain Injury

To investigate the integrity of the default-mode network (DMN) by using independent component analysis (ICA) methods in patients shortly after mild traumatic brain injury (MTBI) and healthy control subjects, and to correlate DMN connectivity changes with neurocognitive tests and clinical symptoms. This study was approved by the institutional review board and complied with HIPAA regulations. Twenty-three patients with MTBI who had posttraumatic symptoms shortly after injury (<2 months) and 18 age-matched healthy control subjects were included in this study. Resting-state functional magnetic resonance imaging was performed at 3 T to characterize the DMN by using ICA methods, including a single-participant ICA on the basis of a comprehensive template from core seeds in the posterior cingulate cortex (PCC) and medial prefrontal cortex (MPFC) nodes. ICA z images of DMN components were compared between the two groups and correlated with neurocognitive tests and clinical performance in patients by using Pearson and Spearman rank correlation. When compared with the control subjects, there was significantly reduced connectivity in the PCC and parietal regions and increased frontal connectivity around the MPFC in patients with MTBI (P < .01). These frontoposterior opposing changes within the DMN were significantly correlated (r = -0.44, P = .03). The reduced posterior connectivity correlated positively with neurocognitive dysfunction (eg, cognitive flexibility), while the increased frontal connectivity correlated negatively with posttraumatic symptoms (ie, depression, anxiety, fatigue, and postconcussion syndrome). These results showed abnormal DMN connectivity patterns in patients with MTBI, which may provide insight into how neuronal communication and information integration are disrupted among DMN key structures after mild head injury.

Age effect on the default mode network, inner thoughts, and cognitive abilities

Age-related effects on the default mode network (DMN) connectivity as measured at rest using functional magnetic resonance imaging (fMRI) are now well described. Little is known however about the relationships between these changes and age-related effects on cognition or on the unconstrained thoughts which occur during the resting-state scan, called inner experience. Brain resting-state activity, inner experience, and cognitive ability measurements were obtained in 70 participants aged 19–80 years. The anterior-posterior disruption of DMN activity with age reported in previous studies was recovered here. A significant effect of age was also found on cognitive abilities but not on inner experience. Finally, age-related changes in DMN connectivity were found to correlate with cognitive abilities, and more specifically with autobiographical memory performance. These findings provide new information to fuel the debate on the role of the brain default mode and more specifically on the effect of age-related changes in resting-state activity as measured with fMRI.

Development of functional and structural connectivity within the default mode network in young children

Functional and structural maturation of networks comprised of discrete regions is an important aspect of brain development. The default-mode network (DMN) is a prominent network which includes the posterior cingulate cortex (PCC), medial prefrontal cortex (mPFC), medial temporal lobes (MTL), and angular gyrus (AG). Despite increasing interest in DMN function, little is known about its maturation from childhood to adulthood. Here we examine developmental changes in DMN connectivity using a multimodal imaging approach by combining resting-state fMRI, voxel-based morphometry and diffusion tensor imaging-based tractography. We found that the DMN undergoes significant developmental changes in functional and structural connectivity, but these changes are not uniform across all DMN nodes. Convergent structural and functional connectivity analyses suggest that PCC-mPFC connectivity along the cingulum bundle is the most immature link in the DMN of children. Both PCC and mPFC also showed gray matter volume differences, as well as prominent macrostructural and microstructural differences in the dorsal cingulum bundle linking these regions. Notably, structural connectivity between PCC and left MTL was either weak or non-existent in children, even though functional connectivity did not differ from that of adults. These results imply that functional connectivity in children can reach adult-like levels despite weak structural connectivity. We propose that maturation of PCC-mPFC structural connectivity plays an important role in the development of self-related and social-cognitive functions that emerge during adolescence. More generally, our study demonstrates how quantitative multimodal analysis of anatomy and connectivity allows us to better characterize the heterogeneous development and maturation of brain networks.