Connectivity Of DMN Research Articles

Effects of Cortisol Administration on Resting-State Functional Connectivity in Women with Depression

Previous resting-state functional connectivity (rsFC) research has identified several brain networks impacted by depression and cortisol, including default mode (DMN), frontoparietal (FPN), and salience networks (SN). In the present study, we examined the effects of cortisol administration on rsFC of these networks in individuals varying in depression history and severity. We collected resting-state fMRI scans and self-reported depression symptom severity for 74 women with and without a history of depression after cortisol and placebo administration using a double-blind, crossover design. We conducted seed-based rsFC analyses for DMN, FPN, and SN seeds to examine rsFC changes after cortisol vs. placebo administration in relation to depression history group and severity. Results revealed a main effect of depression group, with lower left amygdala (SN)-middle temporal gyrus connectivity in women with a history of depression. Cortisol administration increased insula (SN)-inferior frontal gyrus and superior temporal gyrus connectivity. We also found that greater depression severity was associated with increased PCC (DMN)-cerebellum connectivity after cortisol. These results did not survive Bonferroni correction for seed ROIs and should be interpreted with caution. Our findings indicate that acute cortisol elevation may normalize aberrant connectivity of DMN and SN regions, which could help inform clinical treatments for depression.

Resting‐State Connectivity Changes in Older Adults with Sleep Disturbance

AbstractBackgroundSleep and related disorders could lead to changes in various brain network connectivities, but little is known about the role of Aβ burden—a key Alzheimer’s disease (AD) biomarker—in the relationship between sleep disturbance and altered functional connectivity in older adults. This study examined the association between sleep disturbance, Aβ positivity, and with‐in and between resting‐state functional connectivity networks using a large‐scale dataset from the Alzheimer’s Disease Neuroimaging Initiative (ADNI).MethodSample was consisted of 413 individuals (mean age 76.56±7.20; 57.5% cognitively normal, 30.3% mild cognitive impairment, and 12.1% AD) who had completed sleep measures (Neuropsychiatric Inventory), CSF‐Aβ42 data, and resting‐state fMRI scans at baseline. Functional connectivity within Salience (SN), Default Mode (DMN) and Frontal Parietal networks (FPN) were compared between participants with sleep disturbance versus without sleep disturbance. The interaction between Aβ positivity and sleep disturbance were evaluated controlling for age, diagnosis status, gender, sedatives and hypnotics use, and hypertension.ResultSleep disturbance was associated with reduced connectivity in the SN (β = 0.04, P = 0.006) but not with DMN or FPN. Additionally, sleep disturbance interacted significantly with Aβ positivity in altered with‐in connectivity of SN (β = 0.10, P = 0.003), DMN (β = 0.07, P = 0.0048), and FPN (β = 0.09, P = 0.03) networks.ConclusionSleep disturbance may lead to altered connectivity in the SN and further change various within and between functional networks in the presence of amyloid burden.

Altered dynamic functional network connectivity within default mode network of epileptic children with generalized tonic-clonic seizures

ObjectiveGeneralized tonic-clonic seizures (GTCS) is a group of epileptic disorders characterized by widespread generalized spike-and-waves discharges along with unresponsiveness and convulsions. Abnormal connectivity in the DMN is the common findings in children with generalized epilepsy. However, the neural mechanisms underlying the altered brain connectivity of DMN in children with GTCS remain unclear. The aim of the current study was to explore the temporal properties of functional connectivity states by dynamic functional connectivity (dFC) within the DMN of GTCS children. MethodsWe collected resting-state functional MRI data from 22 GTCS children and 29 age-matched healthy controls. Sliding window approach and k-mean clustering analysis were applied to analyze the dFC and identify transient states of the DMN. Furthermore, the relationship between the dynamic properties and clinical features was assessed. ResultsThe dFC analyses identified two reoccurring states: a more frequent and weak connected state (State 1) and a less frequent and strong connected state (State 2). Relative to the normal control, GTCS children spent more time in State 1 showing weak connections and spent less time in State 2 showing strong connections. Dynamic functional network connectivity strength within the DMN showed both increase and decrease in patient group. In addition, the changes of dynamic metric were found to be correlated with epilepsy duration. SignificantOur findings imply abnormal interactions and the state dynamics in DMN of the children with GTCS. These disruptions of temporal dynamic in DMN may provide significance for understanding the neural mechanism underlying the GTCS in children and suggest that dFC method can be considered as a valuable tool in children with epilepsy.

Perceptual coupling and decoupling are associated with individual differences in working memory encoding and maintenance.

Working memory (WM) allows goal-relevant information to be encoded and maintained in mind, even when the contents of WM are incongruent with the immediate environment. While regions of heteromodal cortex are important for WM, the neural mechanisms that relate to individual differences in the encoding and maintenance of goal-relevant information remain unclear. Here, we used behavioral correlates of two large-scale heteromodal networks at rest, the default mode (DMN) and frontoparietal (FPN) networks, to understand their contributions to distinct features of WM. We assessed each individual’s ability to resist distracting information during the encoding and maintenance phases of a visuospatial WM task. Individuals with stronger connectivity of DMN with medial visual and retrosplenial cortex were less affected by encoding distraction. Conversely, weaker connectivity of both DMN and FPN with visual regions was associated with better WM performance when target information was no longer in the environment and distractors were presented in the maintenance phase. Our study suggests that stronger coupling between heteromodal cortex and visual–spatial regions supports WM encoding by reducing the influence of concurrently presented distractors, while weaker visual coupling is associated with better maintenance of goal-relevant information because it relates to the capacity to ignore task-irrelevant changes in the environment.

Effects of intermittent theta burst stimulation (iTBS) on executive function and neuropsychiatric symptoms in older adults with mild to moderate dementia due to Alzheimer's disease: Preliminary findings of a randomized double‐blind clinical trial

AbstractBackgroundStudies on brain networks indicate that the functional integration between brain networks decreases progressively with Alzheimer`s disease (AD). The intermittent Theta Burst Stimulation (ITBS) has been shown to modulate the connectivity of DMN administered to parietal (PPC) and dorsolateral prefrontal (DLPFC) cortex.MethodWe selected 9 patients with AD, and a randomized double‐blind clinical trial was performed comparing the active iTBS (n=5) with sham group (n=4)of older adults with mild to moderate AD. Active iTBS condition were submitted to 21 iTBS sessions on the right and left DLPFC and the right and left PPC. All participants were assessed at baseline, week 3,week 6, 3 and 6 months. Executive functions were assessed by validated and standardized tests for this population. Behavioral symptoms were evaluated by Neuropsychiatric Inventory (NPI). The changes in performance between assessments were compared using the reliable change index (RCI).ResultOn phonemic verbal fluency two participants from intervention group show decline of this ability. One of them in the 3rd week (RCI = ‐2.16) and in the 6th week (RCI = ‐3.24). And another only in the 6th week (RCI = ‐3.24). After this period, the performance was similar to that of the baseline for both. Despite this, there were three patients who showed change in phonemic verbal fluency in the third week. One participant from sham group also showed improvement in the sixth week (RCI = 2.16).Regarding working memory, a sham participant showed decline in this ability after the sixth week assessment (RCI = ‐7.38) and this performance remained below that presented in the baseline until the sixth month. And another from intervention group showed improvement in the third week (RCI = 2.46), but from the sixth week on, the performance returned to the same level as the baseline.ConclusionThe improvement and impairment of cognitive variables in comparison to baseline was associated with temporal proximity of neurostimulation procedures for both groups. It is still necessary to expand the sample size to clarify which factors impact on this outcomes.

Does resting state functional connectivity differ between mild cognitive impairment and early Alzheimer's dementia?

PurposeThis study aimed to investigate differences in functional connectivity (FC) among different resting state networks (RSN) in clinically non-progressive mild cognitive impairment (MCI) and Alzheimer's disease (AD). MethodsUsing 3T MRI acquired resting-state functional MRI (rs-fMRI), we attempted identification of different RSN using independent component analysis (ICA) in amnestic-MCI, convertors to early AD and age-matched cognitively normal healthy controls. Regions of interest (ROI) that showed significant differences in connectivity on group ICA were selected as seeds for seed-voxel analysis. Group differences in FC for each network-connectivity map were entered into a general linear model with age, gender and total intra-cranial volume (TIV) as covariates. ResultsIn this cross-sectional design 31 HC, 30 MCI and 30 MCI-convertors to early AD were evaluated. Seed-based analysis between AD and controls revealed reduced posterior connectivity within the default mode (DMN), dorsal attention (DAN) and antero-posterior connectivity with sensori-motor (SMN) networks. Reduced cerebellar connectivity of DMN and posterior connectivity within the frontal parietal network (FPN) separated AD from MCI. MCI-control comparisons revealed differences only on ICA. Positive correlation was observed between FC in DMN network clusters with verbal list-learning (r = 0.50) and recall scores (r = 0.51) in AD, the latter additionally demonstrating correlation with SMN clusters (r = 0.50). ConclusionsWidespread network hypo-connectivity is apparent in AD as opposed to MCI non-convertors in comparison to controls, along with positive correlation with memory scores. Reduced connectivity involving DMN and FPN helps to differentiate between AD and MCI-nonconvertors to dementia. Longitudinal studies are required into utility of these measures.

Changes in brain connectivity during a sham-controlled, transcranial magnetic stimulation trial for depression

BackgroundThe subgenual anterior cingulate cortex (sgACC) has been implicated in major depressive disorder (MDD), and this study evaluated sgACC connectivity before and after repetitive transcranial magnetic stimulation (rTMS) treatment. MethodsThirty-two MDD patients entered a sham-controlled, double-blinded, randomized trial of rTMS to the left dorsolateral prefrontal cortex (dlFPC). Subjects underwent resting state functional magnetic resonance imaging before and after 20 sessions of high frequency rTMS. Seed voxels identified the affective network (AN; sgACC, amygdala), default mode network (DMN; posterior cingulate cortex [PCC]), and fronto-parietal network (FPN; dlPFC stimulation site). ResultsThere was no significant effect of active rTMS over sham on the primary outcome measure (Montgomery-Asberg Depression Scale rating), with both groups improving over time, and no specific effect of rTMS (sham vs active) on connectivity. However, among patients who showed significant improvement, sgACC connectivity decreased for sham (to AN, trend to DMN) and active rTMS responders (to AN, DMN, FPN), but not in non-responders, who tended to maintain connectivity. Including subjects who started with sham but then received open-label active treatment, baseline connectivity from the PCC to the anterior insula was greater in non-responders compared to responders (n = 27, excluding 5 sham responders). LimitationsThe sample size was small; the stimulation target was non-standard, and the lack of a significant clinical effect of rTMS limits conclusions about negative findings. ConclusionssgACC connectivity reduces along with depressive symptoms, not specific to rTMS therapy. Altered connectivity of DMN with anterior insula may reflect a type of patient less likely to respond to an intervention.

Aberrant functional networks connectivity and structural atrophy in silent lacunar infarcts: relationship with cognitive impairments.

Silent or asymptomatic lacunar infarcts (LACI) are common in elderly individuals, but it remains largely unclear how these often neglected silent brain infarcts lead to multiple domain cognitive deficits and even Alzheimer's disease (AD). In this study, we investigated the difference between patients with silent LACI in basal ganglia region and healthy controls for the structural and functional changes in the aspects of alterations of gray matter (GM) volume and intra-/inter-default mode network (DMN) and salience network (SN) connectivity. Thirty patients with silent LACI in the basal ganglia region and thirty healthy controls participated in the study. Voxel-based morphometry analysis was employed to measure the GM volume. We further investigated the intra/inter-network connectivity of DMN and SN using resting-state functional magnetic resonance imaging. Compared with healthy controls, patients performed worse in cognitive function in the aspects of general mental status, attention, and memory. The LACIs showed more severe GM atrophy in insula, anterior cingulate cortex, caudate, and superior temporal pole than controls. The connectivity within and between two networks was also reduced in patients. Importantly, the disrupted connectivity correlated with the patients' cognitive performance. Our findings support the hypothesis that silent lacunar infarcts result in cognitive decline, GM, and functional connectivity loss.