Cardiorespiratory fitness predicts effective connectivity between the hippocampus and default mode network nodes in young adults

Rodent and human studies examining the relationship between aerobic exercise, brain structure, and brain function indicate that the hippocampus (HC), a brain region critical for episodic memory, demonstrates striking plasticity in response to exercise. Beyond the hippocampal memory system, human studies also indicate that aerobic exercise and cardiorespiratory fitness (CRF) are associated with individual differences in large‐scale brain networks responsible for broad cognitive domains. Examining network activity in large‐scale resting‐state brain networks may provide a link connecting the observed relationships between aerobic exercise, hippocampal plasticity, and cognitive enhancement within broad cognitive domains. Previously, CRF has been associated with increased functional connectivity of the default mode network (DMN), specifically in older adults. However, how CRF relates to the magnitude and directionality of connectivity, or effective connectivity, between the HC and other DMN nodes remains unknown. We used resting‐state fMRI and conditional Granger causality analysis (CGCA) to test the hypothesis that CRF positively predicts effective connectivity between the HC and other DMN nodes in healthy young adults. Twenty‐six participants (ages 18–35 years) underwent a treadmill test to determine CRF by estimating its primary determinant, maximal oxygen uptake (V^.O_2max), and a 10‐min resting‐state fMRI scan to examine DMN effective connectivity. We identified the DMN using group independent component analysis and examined effective connectivity between nodes using CGCA. Linear regression analyses demonstrated that CRF significantly predicts causal influence from the HC to the ventromedial prefrontal cortex, posterior cingulate cortex, and lateral temporal cortex and to the HC from the dorsomedial prefrontal cortex. The observed relationship between CRF and hippocampal effective connectivity provides a link between the rodent literature, which demonstrates a relationship between aerobic exercise and hippocampal plasticity, and the human literature, which demonstrates a relationship between aerobic exercise and CRF and the enhancement of broad cognitive domains including, but not limited to, memory.     

The retrosplenial cortex: A memory gateway between the cortical default mode network and the medial temporal lobe

The default mode network (DMN) involves interacting cortical areas, including the posterior cingulate cortex (PCC) and the retrosplenial cortex (RSC), and subcortical areas, including the medial temporal lobe (MTL). The degree of functional connectivity (FC) within the DMN, particularly between MTL and medial‐parietal subsystems, relates to episodic memory (EM) processes. However, past resting‐state studies investigating the link between posterior DMN‐MTL FC and EM performance yielded inconsistent results, possibly reflecting heterogeneity in the degree of connectivity between MTL and specific cortical DMN regions. Animal work suggests that RSC has structural connections to both cortical DMN regions and MTL, and may thus serve as an intermediate layer that facilitates information transfer between cortical and subcortical DMNs. We studied 180 healthy old adults (aged 64–68 years), who underwent comprehensive assessment of EM, along with resting‐state fMRI. We found greater FC between MTL and RSC than between MTL and the other cortical DMN regions (e.g., PCC), with the only significant association with EM observed for MTL‐RSC FC. Mediational analysis showed that MTL‐cortical DMN connectivity increased with RSC as a mediator. Further analysis using a graph‐theoretical approach on DMN nodes revealed the highest betweenness centrality for RSC, confirming that a high proportion of short paths among DMN regions pass through RSC. Importantly, the degree of RSC mediation was associated with EM performance, suggesting that individuals with greater mediation have an EM advantage. These findings suggest that RSC forms a critical gateway between MTL and cortical DMN to support EM in older adults.     

抑郁症静息态默认状态网络内功能连接的初步探讨

目的 通过分析静息态下抑郁症患者默认状态网络内脑区间功能连接效能,探讨默认状态网络在抑郁症病理机制中的作用.方法 15例符合中国精神障碍分类及诊断标准第3版(CCMD-3)抑郁发作和美国精神障碍诊断与统计手册第4版(DSM-Ⅳ)重性抑郁症诊断标准的首发抑郁症患者与14名正常对照完成功能磁共振成像扫描.分析受试者默认状态网络内脑区的功能连接强度并比较其组问差异.结果 与正常对照比较,抑郁症患者双侧前额中部与楔前叶、双侧后扣带回与前额中部、右后扣带回与楔前叶、双侧前扣带回腹侧与前额中部的功能连接减低(P＜0.05).结论 静息态下抑郁症患者默认状态网络内脑区间的连接效能存在异常,这可能在抑郁症的病理机制中发挥了重要作用.     

部分性发作癫痫患者静息状态功能磁共振默认模式网络的功能连接改变

目的 应用静息状态功能磁共振成像(fMRI)探讨部分性发作癫痫患者静息状态下的脑功能改变.方法 对60例部分性发作癫痫患者(患者组)和60名性别、年龄和教育程度匹配的健康对照者(对照组),使用3.0T磁共振采集两组的静息状态下fMRI数据,采用功能连接方法分析计算脑区的默认模式网络的功能连接,利用SPM5软件分析比较患者组和对照组脑功能的差异.结果 患者组的默认模式网络的功能连接主要包括左侧楔前叶/后扣带回和角回、扣带回;对照组的功能连接主要包括左侧楔前叶/后扣带回和右侧角回,双侧内侧额叶和颞叶;患者组的左侧顶下小叶[坐标值(x,y,z):-57,-39,48;t=4.90,P＜0.01]、左侧缘上回[坐标值(x,y,z):-63,- 48,33;t=4.25,P＜0.01]、左侧海马旁回[坐标值(x,y,z):-30,-6,-21;t =4.05,P＜0.01]、左侧颞上回[坐标值(x,y,z):-48,-39,6;t=3.72,P＜0.01],左侧钩回[坐标值(x,y,z):-24,6,- 36;=4.56,P＜0.01]及右侧钩回[坐标值(x,y,z):33,-15,- 36;t=4.00,P＜0.01]的默认模式网络功能连接较对照组降低;未发现功能连接升高的脑区.结论 部分性发作癫痫患者静息状态下脑区的功能连接改变,可能是部分性发作癫痫潜在的病理生理机制.静息状态fMRI能发现常规MRI正常的癫痫患者的广泛脑功能异常,是一种无创的研究癫痫患者脑功能的有效方法.     

Frontoparietal and default mode network connectivity varies with age and intelligence

BackgroundAnticorrelated resting state connectivity between task-positive and task-negative networks in adults supports flexible shifting between externally focused attention and internal thought. Findings suggest that children show positive correlations between task-positive (frontoparietal; FP) and task-negative (default mode; DMN) networks. FP-DMN connectivity also associates with intellectual functioning across the lifespan. We investigated whether FP-DMN connectivity in healthy children varied with age and intelligence quotient (IQ).MethodsWe utilized network-based statistics (NBS) to examine resting state functional connectivity between FP and DMN seeds in N = 133 7−25-year-olds (M_age = 15.80). Linear regression evaluated FP-DMN associations with IQ.ResultsWe detected NBS subnetworks containing both within- and between-network connections that were inversely associated with age. Four FP-DMN connections showed more negative connectivity between FP (inferior frontal gyrus and precentral gyrus) and DMN regions (frontal medial cortex, precuneus, and frontal pole) among older participants. Frontal pole-precentral gyrus connectivity inversely associated with IQ.ConclusionsFP-DMN connectivity was more anticorrelated at older ages, potentially indicating dynamic network segregation of these circuits from childhood to early adulthood. Youth with more mature (i.e., anticorrelated) FP-DMN connectivity demonstrated higher IQ. Our findings add to the growing body of literature examining neural network development and its association with IQ.     

The brain functional connectivity in the default mode network is associated with self-efficacy in young adults

Brain Imaging and Behavior - Self-efficacy is a subjective belief that depends on self-related past experience, and is a strong predictor for individual future performance. To the aim of promoting...     

Direct connections between the hippocampus and the retrosplenial cortex in the rat

The connections of the retrosplenial field of the limbic cortex and hippocampal formation in the rat were studied by the horseradish peroxidase method. After dry horseradish peroxidase application into dorsocaudal part of the retrosplenial cortex labelled cells were found in the rostral pole of the hippocampal field Ca3 and in the presubiculum. After ionophoretic injection of HRP into the rostral pole of the hippocamp labelled cells were found in the layers V and VI of the retrosplenial field of the limbic cortex and in the prosubiculum. The data obtained show reciprocal direct connections between the rostral pole of the hippocamp and retrosplenial field of the limbic cortex, as well as direct efferent projections of the dorsal subiculum to the rostral pole of the hippocamp.     

Altered resting state connectivity of the default mode network in alexithymia

Alexithymia is a trait characterized by a diminished capacity to describe and distinguish emotions and to fantasize; it is associated with reduced introspection and problems in emotion processing. The default mode network (DMN) is a network of brain areas that is normally active during rest and involved in emotion processing and self-referential mental activity, including introspection. We hypothesized that connectivity of the DMN might be altered in alexithymia. Twenty alexithymic and 18 non-alexithymic healthy volunteers underwent a resting state fMRI scan. Independent component analysis was used to identify the DMN. Differences in connectivity strength were compared between groups. Within the DMN, alexithymic participants showed lower connectivity within areas of the DMN (medial frontal and temporal areas) as compared to non-alexithymic participants. In contrast, connectivity in the high-alexithymic participants was higher for the sensorimotor cortex, occipital areas and right lateral frontal cortex than in the low-alexithymic participants. These results suggest a diminished connectivity within the DMN of alexithymic participants, in brain areas that may also be involved in emotional awareness and self-referential processing. On the other hand, alexithymia was associated with stronger functional connections of the DMN with brain areas involved in sensory input and control of emotion.     

High-resolution functional connectivity of the default mode network in young adults with down syndrome

Studies of resting-state functional connectivity MRI in Alzheimer’s disease suggest that disease stage plays a role in functional changes of the default mode network. Individuals with the genetic disorder Down syndrome show an increased incidence of early-onset Alzheimer’s-type dementia, along with early and nearly universal neuropathologic changes of Alzheimer’s disease. The present study examined high-resolution functional connectivity of the default mode network in 11 young adults with Down syndrome that showed no measurable symptoms of dementia and 11 age- and sex-matched neurotypical controls. We focused on within-network connectivity of the default mode network, measured from both anterior and posterior aspects of the cingulate cortex. Sixty-eight percent of connections to the posterior cingulate and 26% to the anterior cingulate showed reduced strength in the group with Down syndrome (p < 0.01). The Down syndrome group showed increased connectivity strength from the anterior cingulate to the bilateral inferior frontal gyri and right putamen (p < 0.005). In an exploratory analysis, connectivity in the group with Down syndrome showed regional relationships to plasma measures of inflammatory markers and t-tau. In non-demented adults with Down syndrome, functional connectivity within the default mode network may be analogous to changes reported in preclinical Alzheimer’s disease, and warrants further investigation as a measure of dementia risk.

     

Changes in the default mode network in the prefrontal lobe, posterior cingulated cortex and hippocampus of heroin users

The default mode network is associated with senior cognitive functions in humans. In this study, we performed independent component analysis of blood oxygenation signals from 14 heroin users and 13 matched normal controls in the resting state through functional MRI scans. Results showed that the default mode network was significantly activated in the prefrontal lobe, posterior cingulated cortex and hippocampus of heroin users, and an enhanced activation signal was observed in the right inferior parietal lobule (P < 0.05, corrected for false discovery rate). Experimental findings indicate that the default mode network is altered in heroin users.     

Metabolic syndrome components moderate the association between executive function and functional connectivity in the default mode network

Middle aged individuals with Metabolic Syndrome are at high risk for cognitive decline. Dyssynchrony in the resting state Default Mode Network is one early indicator of brain vulnerability. We set out to explore the relationship between default mode resting state functional connectivity and cognitive performance in both memory and executive domains at midlife in the presence of Metabolic Syndrome components. Seed-based Correlation Analyses were performed between the seed voxel in the posterior cingulate cortex and the medial prefrontal cortex on 200 participants (ages 40–61). Executive domain scores were significantly predicted by the interaction between number of Metabolic Syndrome components and resting state connectivity in the Default Mode Network (p = .004) such that connectivity was negatively related to executive function at higher numbers of Metabolic Syndrome components. Results were not significant for memory. Our findings indicate that clusters of cardiovascular disease risk factors alter functional relationships in the brain and highlights the need to continue exploring how compensatory techniques might operate to support cognitive performance at midlife.

     

Structural and functional connectivity of the precuneus and thalamus to the default mode network

Neuroimaging studies have identified functional interactions between the thalamus, precuneus, and default mode network (DMN) in studies of consciousness. However, less is known about the structural connectivity of the precuneus and thalamus to regions within the DMN. We used diffusion tensor imaging (DTI) to parcellate the precuneus and thalamus based on their probabilistic white matter connectivity to each other and DMN regions of interest (ROIs) in 37 healthy subjects from the Human Connectome Database. We further assessed resting‐state functional connectivity (RSFC) among the precuneus, thalamus, and DMN ROIs. The precuneus was found to have the greatest structural connectivity with the thalamus, where connection fractional anisotropy (FA) increased with age. The precuneus also showed significant structural connectivity to the hippocampus and middle pre‐frontal cortex, but minimal connectivity to the angular gyrus and midcingulate cortex. In contrast, the precuneus exhibited significant RSFC with the thalamus and the strongest RSFC with the AG. Significant symmetrical structural connectivity was found between the thalamus and hippocampus, mPFC, sFG, and precuneus that followed known thalamocortical pathways, while thalamic RSFC was strongest with the precuneus and hippocampus. Overall, these findings reveal high levels of structural and functional connectivity linking the thalamus, precuneus, and DMN. Differences between structural and functional connectivity (such as between the precuneus and AG) may be interpreted to reflect dynamic shifts in RSFC for cortical hub‐regions involved with consciousness, but could also reflect the limitations of DTI to detect superficial white matter tracts that connect cortico‐cortical regions. Hum Brain Mapp 38:938–956, 2017. © 2016 Wiley Periodicals, Inc.     

Subthreshold depression is associated with impaired resting-state functional connectivity of the cognitive control network

Subthreshold depression (StD) is a prevalent condition associated with social morbidity and increased service utilization, as well as a high risk of developing into a major depressive disorder (MDD). The lack of well-defined diagnostic criteria for StD has limited research on this disorder, with very few brain-imaging studies examining the neurobiology of StD. Yet, identifying the neural pathology of StD has the potential to elucidate risk factors and prognostic markers for major depression and is crucial for developing tailored treatments for patients at mild stages of depression. We investigated resting-state functional connectivity (rs-FC) of the cognitive control network (CCN), known to be dysregulated in MDD, using the bilateral dorsolateral prefrontal cortex (DLPFC) as a seed, focusing on two cohorts of StD subjects (young and middle aged) as well as matched controls. Irrespective of age, we found a significant rs-FC decrease in the CCN of the StD subjects, compared with matched controls, particularly between the DLPFC and the brain regions associated with the representation of self and other mental states (temporo-parietal junction (TPJ) and precuneus), as well as salience detection and orienting (insula). The functional connectivity between the DLPFC and the left TPJ was also associated with depressive symptom scores measured by the Center for Epidemiologic Studies Depression Scale. This finding may shed light on the neural pathology of StD, leading to better understanding of mild stages of depression, its diagnosis and the development of new treatments.     

Limbic links to paranoia: increased resting-state functional connectivity between amygdala,hippocampus and orbitofrontal cortex in schizophrenia patients with paranoia

European Archives of Psychiatry and Clinical Neuroscience - Paranoia is a frequent and highly distressing experience in psychosis. Models of paranoia suggest limbic circuit pathology. Here, we...     

Effect of chemotherapy on default mode network connectivity in older women with breast cancer

Brain Imaging and Behavior - Chemotherapy may impair cognition and contribute to accelerated aging. The purpose of this study was to assess the effects of chemotherapy on the connectivity of the...     

Hemispheric asymmetries of functional connectivity and grey matter volume in the default mode network

Resting state networks such as the default mode network have been widely reported. Although a plethora of information on its functional relevance has been generated, little is known about lateralization or hemisphere asymmetry within the DMN. We used high-resolution resting state fMRI and T1 3D data to investigate such asymmetries in two groups of healthy subjects, one right-handed and one left-handed. Independent component analysis and the dual regression approach were carried out to identify functional asymmetries, while voxel-based morphometry was used to identify structural asymmetries in grey matter volume within the DMN. Greater leftward functional connectivity was observed in the posterior cingulate gyrus (PCG) for both groups. Leftward functional asymmetry was observed in the thalamus and rightward functional asymmetries were observed in the middle frontal and middle/superior temporal gyrus in the right-handed group. Rightward asymmetries in grey matter volume were observed in the posterior portion of the PCG for both groups. The right-handed group exhibited leftward structural asymmetries in the anterior portion of the PCG and in the middle frontal and posterior portion of the middle temporal gyrus, while rightward asymmetries were observed in the posterior portion of the PCG and anterior portions of temporal regions. These results suggest that functional connectivity and grey matter volume are not equally distributed between hemispheres within the DMN, and that functional asymmetries are not always reflected or determined by structural asymmetries.