Shifting brain asymmetry: the link between meditation and structural lateralization

Previous studies have revealed an increased fractional anisotropy and greater thickness in the anterior parts of the corpus callosum in meditation practitioners compared with control subjects. Altered callosal features may be associated with an altered inter-hemispheric integration and the degree of brain asymmetry may also be shifted in meditation practitioners. Therefore, we investigated differences in gray matter asymmetry as well as correlations between gray matter asymmetry and years of meditation practice in 50 long-term meditators and 50 controls. We detected a decreased rightward asymmetry in the precuneus in meditators compared with controls. In addition, we observed that a stronger leftward asymmetry near the posterior intraparietal sulcus was positively associated with the number of meditation practice years. In a further exploratory analysis, we observed that a stronger rightward asymmetry in the pregenual cingulate cortex was negatively associated with the number of practice years. The group difference within the precuneus, as well as the positive correlations with meditation years in the pregenual cingulate cortex, suggests an adaptation of the default mode network in meditators. The positive correlation between meditation practice years and asymmetry near the posterior intraparietal sulcus may suggest that meditation is accompanied by changes in attention processing.     

Default mode network deactivation during odor–visual association

Default mode network (DMN) deactivation has been shown to be functionally relevant for goal‐directed cognition. In this study, the DMN's role during olfactory processing was investigated using two complementary functional magnetic resonance imaging (fMRI) paradigms with identical timing, visual‐cue stimulation, and response monitoring protocols. Twenty‐nine healthy, non‐smoking, right‐handed adults (mean age = 26 ± 4 years, 16 females) completed an odor–visual association fMRI paradigm that had two alternating odor + visual and visual‐only trial conditions. During odor + visual trials, a visual cue was presented simultaneously with an odor, while during visual‐only trial conditions the same visual cue was presented alone. Eighteen of the twenty‐nine participants (mean age = 27.0 ± 6.0 years, 11 females) also took part in a control no‐odor fMRI paradigm that consisted of a visual‐only trial condition which was identical to the visual‐only trials in the odor–visual association paradigm. Independent Component Analysis (ICA), extended unified structural equation modeling (euSEM), and psychophysiological interaction (PPI) were used to investigate the interplay between the DMN and olfactory network. In the odor–visual association paradigm, DMN deactivation was evoked by both the odor + visual and visual‐only trial conditions. In contrast, the visual‐only trials in the no‐odor paradigm did not evoke consistent DMN deactivation. In the odor–visual association paradigm, the euSEM and PPI analyses identified a directed connectivity between the DMN and olfactory network which was significantly different between odor + visual and visual‐only trial conditions. The results support a strong interaction between the DMN and olfactory network and highlights the DMN's role in task‐evoked brain activity and behavioral responses during olfactory processing. Hum Brain Mapp 38:1125–1139, 2017. © 2016 Wiley Periodicals, Inc.     

Studying the default mode and its mindfulness-induced changes using EEG functional connectivity

The default mode network (DMN) has been largely studied by imaging, but not yet by neurodynamics, using electroencephalography (EEG) functional connectivity (FC). mindfulness meditation (MM), a receptive, non-elaborative training is theorized to lower DMN activity. We explored: (i) the usefulness of EEG-FC for investigating the DMN and (ii) the MM-induced EEG-FC effects. To this end, three MM groups were compared with controls, employing EEG-FC (–MPC, mean phase coherence). Our results show that: (i) DMN activity was identified as reduced overall inter-hemispheric gamma MPC during the transition from resting state to a time production task and (ii) MM-induced a state increase in alpha MPC as well as a trait decrease in EEG-FC. The MM-induced EEG-FC decrease was irrespective of expertise or band. Specifically, there was a relative reduction in right theta MPC, and left alpha and gamma MPC. The left gamma MPC was negatively correlated with MM expertise, possibly related to lower internal verbalization. The trait lower gamma MPC supports the notion of MM-induced reduction in DMN activity, related with self-reference and mind-wandering. This report emphasizes the possibility of studying the DMN using EEG-FC as well as the importance of studying meditation in relation to it.     

Default and control network connectivity dynamics track the stream of affect at multiple timescales

In everyday life, the stream of affect results from the interaction between past experiences, expectations and the unfolding of events. How the brain represents the relationship between time and affect has been hardly explored, as it requires modeling the complexity of everyday life in the laboratory setting. Movies condense into hours a multitude of emotional responses, synchronized across subjects and characterized by temporal dynamics alike real-world experiences. Here, we use time-varying intersubject brain synchronization and real-time behavioral reports to test whether connectivity dynamics track changes in affect during movie watching. The results show that polarity and intensity of experiences relate to the connectivity of the default mode and control networks and converge in the right temporoparietal cortex. We validate these results in two experiments including four independent samples, two movies and alternative analysis workflows. Finally, we reveal chronotopic connectivity maps within the temporoparietal and prefrontal cortex, where adjacent areas preferentially encode affect at specific timescales.     

Stepwise functional connectivity reveals altered sensory‐multimodal integration in medication‐naïve adults with attention deficit hyperactivity disorder

Neuroimaging studies indicate that children with attention‐deficit/hyperactivity disorder (ADHD) present alterations in several functional networks of the sensation‐to‐cognition spectrum. These alterations include functional overconnectivity within sensory regions and underconnectivity between sensory regions and neural hubs supporting higher order cognitive functions. Today, it is unknown whether this same pattern of alterations persists in adult patients with ADHD who had never been medicated for their condition. The aim of the present study was to assess whether medication‐naïve adults with ADHD presented alterations in functional networks of the sensation‐to‐cognition spectrum. Thirty‐one medication‐naïve adults with ADHD and twenty‐two healthy adults underwent resting‐state functional magnetic resonance imaging (rs‐fMRI). Stepwise functional connectivity (SFC) was used to characterize the pattern of functional connectivity between sensory seed regions and the rest of the brain at direct, short, intermediate, and long functional connectivity distances, thus covering the continuum from the sensory input to the neural hubs supporting higher order cognitive functions. As compared to controls, adults with ADHD presented increased SFC degree within primary sensory regions and decreased SFC degree between sensory seeds and higher order integration nodes. In addition, they exhibited decreased connectivity degree between sensory seeds and regions of the default‐mode network. Consistently, the higher the score in clinical severity scales the lower connectivity degree between seed regions and the default mode network.     

Basal ganglia atrophy–associated causal structural network degeneration in Parkinson's disease

Parkinson''s disease (PD) is a progressive neurodegenerative disease characterized by both motor and non‐motor symptoms. A convergent pathophysiological hallmark of PD is an early selective vulnerability within the basal ganglia circuit. However, the causal interactions between basal ganglia atrophy and progressive structural network alterations in PD remain unaddressed. Here, we adopted voxel‐based morphometry method to measure gray matter (GM) volume for each participant (n = 84 PD patients and n = 70 matched healthy controls). Patients were first divided into three stages according to the Hoehn and Yahr (H&Y) and the Part III of Unified Parkinson''s Disease Rating Scale scores respectively to analyze the stage‐specific GM atrophy patterns. Then, the modulation of early caudate atrophy over other brain structures was evaluated using the whole‐brain voxel‐wise and region‐of‐interest‐wise causal structural covariance network approaches. We found that GM atrophy progressively expands from the basal ganglia to the angular gyrus, temporal areas, and eventually spreads through the subcortical–cortical networks as PD progresses. Notably, we identified a shared caudate‐associated degeneration network including the basal ganglia, thalamus, cerebellum, sensorimotor cortex, and cortical association areas with the PD progressive factors. These findings suggest that the early structural vulnerability of basal ganglia in PD may play a pivotal role in the modulation of motor and non‐motor circuits at the structural level. Our work provides evidence for a novel mechanism of network degeneration that underlies the pathology of PD and may have potential clinical applications in the development of early predictors of PD onset and progress.     

An examination of the default mode network in individuals with autonomous sensory meridian response (ASMR)

Autonomous Sensory Meridian Response (ASMR) is a perceptual condition in which specific visual and auditory stimuli consistently trigger tingling sensations on the scalp and neck, sometimes spreading to the back and limbs. These triggering stimuli are often social, almost intimate, in nature (e.g., hearing whispering, or watching someone brush her hair), and often elicit a calm and positive emotional state. Surprisingly, despite its prevalence in the general population, no published study has examined the neural underpinnings of ASMR. In the current study, the default mode network (DMN) of 11 individuals with ASMR was contrasted to that of 11 matched controls. The results indicated that the DMN of individuals with ASMR showed significantly less functional connectivity than that of controls. The DMN of individuals with ASMR also demonstrated increased connectivity between regions in the occipital, frontal, and temporal cortices, suggesting that ASMR was associated with a blending of multiple resting-state networks. This atypical functional connectivity likely influences the unique sensory-emotional experiences associated with ASMR.     

Neurochemical correlates of scene processing in the precuneus/posterior cingulate cortex: A multimodal fMRI and 1H‐MRS study

Precuneus/posterior cingulate cortex (PCu/PCC) are key components of a midline network, activated during rest but also in tasks that involve construction of scene or situation models. Despite growing interest in PCu/PCC functional alterations in disease and disease risk, the underlying neurochemical modulators of PCu/PCC's task‐evoked activity are largely unstudied. Here, a multimodal imaging approach was applied to investigate whether interindividual differences in PCu/PCC fMRI activity, elicited during perceptual discrimination of scene stimuli, were correlated with local brain metabolite levels, measured during resting‐state ¹H‐MRS. Forty healthy young adult participants completed an fMRI perceptual odd‐one‐out task for scenes, objects and faces. ¹H‐MRS metabolites N‐acetyl‐aspartate (tNAA), glutamate (Glx) and γ‐amino‐butyric acid (GABA+) were quantified via PRESS and MEGA‐PRESS scans in a PCu/PCC voxel and an occipital (OCC) control voxel. Whole brain fMRI revealed a cluster in right dorsal PCu/PCC that showed a greater BOLD response to scenes versus faces and objects. When extracted from an independently defined PCu/PCC region of interest, scene activity (vs. faces and objects and also vs. baseline) was positively correlated with PCu/PCC, but not OCC, tNAA. A voxel‐wise regression analysis restricted to the PCu/PCC ¹H‐MRS voxel area identified a significant PCu/PCC cluster, confirming the positive correlation between scene‐related BOLD activity and PCu/PCC tNAA. There were no correlations between PCu/PCC activity and Glx or GABA+ levels. These results demonstrate, for the first time, that scene activity in PCu/PCC is linked to local tNAA levels, identifying a neurochemical influence on interindividual differences in the task‐driven activity of a key brain hub.     

Dynamic changes of ICA‐derived EEG functional connectivity in the resting state

An emerging issue in neuroscience is how to identify baseline state(s) and accompanying networks termed “resting state networks” (RSNs). Although independent component analysis (ICA) in fMRI studies has elucidated synchronous spatiotemporal patterns during cognitive tasks, less is known about the changes in EEG functional connectivity between eyes closed (EC) and eyes open (EO) states, two traditionally used baseline indices. Here we investigated healthy subjects (n = 27) in EC and EO employing a four‐step analytic approach to the EEG: (1) group ICA to extract independent components (ICs), (2) standardized low‐resolution tomography analysis (sLORETA) for cortical source localization of IC network nodes, followed by (3) graph theory for functional connectivity estimation of epochwise IC band‐power, and (4) circumscribing IC similarity measures via hierarchical cluster analysis and multidimensional scaling (MDS). Our proof‐of‐concept results on alpha‐band power demonstrate five statistically clustered groups with frontal, central, parietal, occipitotemporal, and occipital sources. Importantly, during EO compared with EC, graph analyses revealed two salient functional networks with frontoparietal connectivity: a more medial network with nodes in the mPFC/precuneus which overlaps with the “default‐mode network” (DMN), and a more lateralized network comprising the middle frontal gyrus and inferior parietal lobule, coinciding with the “dorsal attention network” (DAN). Furthermore, a separate MDS analysis of ICs supported the emergence of a pattern of increased proximity (shared information) between frontal and parietal clusters specifically for the EO state. We propose that the disclosed component groups and their source‐derived EEG functional connectivity maps may be a valuable method for elucidating direct neuronal (electrophysiological) RSNs in healthy people and those suffering from brain disorders. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.     

Brain default-mode network abnormalities in hepatic encephalopathy: a resting-state functional MRI study

Many neuroimaging investigations focus on hepatic encephalopathy (HE); however, few investigate default-mode network (DMN) in the patients with HE and its underlying physiological relevance using resting-state fMRI. In this study, independent component analysis was used to retrieve components representing the DMN of patients with HE (n = 14) and healthy volunteers (n = 14). Four patients were excluded because of head motion (n = 3) and the artifact from the artificial tooth (n = 1). Comparison results between the two groups revealed significantly reduced functional connectivity in the right middle frontal gyrus and left posterior cingulate cortex in the HE patients. A statistical t-map from the comparison of venous blood ammonia levels and the z-scores of the DMN obtained from independent component analysis was computed in the HE group, which showed negative correlation with the changes in left angular gyrus. In conclusions, resting-state fMRI can be used to examine DMN changes in HE patients. Reduced functional connectivity in the right middle frontal gyrus and left posterior cingulate cortex consisting of the DMN and negative correlation between the functional connectivity changes in left AG and the venous blood ammonia levels support the notion of damages in functional organization of the central nervous system in HE patients.     

Partial‐volume modeling reveals reduced gray matter in specific thalamic nuclei early in the time course of psychosis and chronic schizophrenia

The structural complexity of the thalamus, due to its mixed composition of gray and white matter, make it challenging to disjoint and quantify each tissue contribution to the thalamic anatomy. This work promotes the use of partial‐volume‐based over probabilistic‐based tissue segmentation approaches to better capture thalamic gray matter differences between patients at different stages of psychosis (early and chronic) and healthy controls. The study was performed on a cohort of 23 patients with schizophrenia, 41 with early psychosis and 69 age and sex‐matched healthy subjects. Six tissue segmentation approaches were employed to obtain the gray matter concentration/probability images. The statistical tests were applied at three different anatomical scales: whole thalamus, thalamic subregions and voxel‐wise. The results suggest that the partial volume model estimation of gray matter is more sensitive to detect atrophies within the thalamus of patients with psychosis. However all the methods detected gray matter deficit in the pulvinar, particularly in early stages of psychosis. This study demonstrates also that the gray matter decrease varies nonlinearly with age and between nuclei. While a gray matter loss was found in the pulvinar of patients in both stages of psychosis, reduced gray matter in the mediodorsal was only observed in early psychosis subjects. Finally, our analyses point to alterations in a sub‐region comprising the lateral posterior and ventral posterior nuclei. The obtained results reinforce the hypothesis that thalamic gray matter assessment is more reliable when the tissues segmentation method takes into account the partial volume effect.     

Effective connectivity in the default mode network is distinctively disrupted in Alzheimer's disease—A simultaneous resting‐state FDG‐PET/fMRI study

A prominent finding of postmortem and molecular imaging studies on Alzheimer''s disease (AD) is the accumulation of neuropathological proteins in brain regions of the default mode network (DMN). Molecular models suggest that the progression of disease proteins depends on the directionality of signaling pathways. At network level, effective connectivity (EC) reflects directionality of signaling pathways. We hypothesized a specific pattern of EC in the DMN of patients with AD, related to cognitive impairment. Metabolic connectivity mapping is a novel measure of EC identifying regions of signaling input based on neuroenergetics. We simultaneously acquired resting‐state functional MRI and FDG‐PET data from patients with early AD (n = 35) and healthy subjects (n = 18) on an integrated PET/MR scanner. We identified two distinct subnetworks of EC in the DMN of healthy subjects: an anterior part with bidirectional EC between hippocampus and medial prefrontal cortex and a posterior part with predominant input into medial parietal cortex. Patients had reduced input into the medial parietal system and absent input from hippocampus into medial prefrontal cortex (p < 0.05, corrected). In a multiple linear regression with unimodal imaging and EC measures (F _4,25 = 5.63, p = 0.002, r ² = 0.47), we found that EC (β = 0.45, p = 0.012) was stronger associated with cognitive deficits in patients than any of the PET and fMRI measures alone. Our approach indicates specific disruptions of EC in the DMN of patients with AD and might be suitable to test molecular theories about downstream and upstream spreading of neuropathology in AD.     

Reduced functional coupling in the default‐mode network during self‐referential processing

Activity within the default‐mode network (DMN) is thought to be related to self‐referential processing, such as thinking about one's preferences or personality traits. Although the DMN is generally considered to function as a network, evidence is starting to accumulate that suggests that areas of the DMN are each specialized for different subfunctions of self‐referential processing. Here, we address the issue of functional specialization by investigating changes in coupling between areas of the DMN during self‐referential processing. To this aim, brain activity was assessed during a task in which subjects had to indicate whether a trait adjective described their own personality (self‐referential, Self condition), that of another person (other‐referential, Other condition), or whether the trait was socially desirable (nonreferential, Control condition). To exclude confounding effects of cardiorespiratory processes on activity and functional coupling, we corrected the fMRI signal for these effects. Activity within areas of the DMN was found to be modulated by self‐referential processing. More specifically, during the Self condition compared to the Other and Control condition, activity within the dorsal medial prefrontal cortex, ventral medial prefrontal cortex, and posterior cingulate cortex was increased. Moreover, coupling between areas of the DMN was reduced during the Self condition compared to the Other and Control condition, while coupling between regions of the DMN and regions outside the network was increased. As such, these results provide an indication for functional specialization within the DMN and support the notion that each area of the DMN is involved in different subfunctions of self‐referential processing. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

Differential neural activity in the recognition of old versus new events: An Activation Likelihood Estimation Meta‐Analysis

This study presents a meta‐analysis comparing hit and correct rejection (CR) conditions across 48 fMRI studies. Old/new (hit > CR) effects associated most consistently with (1) components of the default‐mode network, including the left angular gyrus, bilateral precuneus, and bilateral posterior cingulate regions, which may support the mental re‐experiencing of an old event, or ecphory; (2) components of the cognitive‐control network, involving the left dorsolateral and dorsomedial prefrontal cortex and bilateral intraparietal sulcus regions, which may mediate memory and non‐memory control functions; and (3) the caudate nucleus, a key part of the brain's reward system that may support the satisfaction tied to target‐detection. Direct comparisons of old/new effects between item versus source retrieval and “remember” versus “know” retrieval yielded three main sets of findings. First, default‐mode network regions showed greater old/new effects in conditions associated with richer ecphoric processing. Second, cognitive‐control network regions showed greater old/new effects in conditions associated with a greater demand for strategic‐retrieval processing. Third, the caudate nucleus showed greater old/new effects in conditions tied to greater confidence in target‐detection. New/old (CR > hit) effects most strongly associated with the bilateral medial temporal lobe, possibly reflecting greater encoding‐related activity for new than for old items, and the right posterior middle temporal regions, possibly reflecting repetition‐related neural priming for old items. In conclusion, neural activity distinguishing old from new events comprises an ensemble of multiple memory‐specific activities, including encoding, retrieval, and priming, as well as multiple types of more general cognitive activities, including default‐mode, cognitive‐control, and reward processing. Hum Brain Mapp, 2013. © 2011 Wiley Periodicals, Inc.     

Association of the ZNF804A gene polymorphism rs1344706 with white matter density changes in Chinese schizophrenia

Background

ZNF804A gene polymorphism rs1344706, the first genetic risk variant to achieve genome wide significance for schizophrenia, has been linked to neural functional connectivity. Dysconnectivity of WM may be the primary pathological mechanism of schizophrenia. Association of this variant with regional WM density has not been investigated in schizophrenic patients.

Methods

69 healthy controls and 80 patients with schizophrenia underwent genotyping of rs1344706 SNPs, and were examined for WM density (T1-weighted MRI). The association of rs1344706 with WM changes in schizophrenia patients and healthy controls was analyzed using a full-factorial 2 × 2 analysis of variance.

Results

1. There was an interaction on WM density in the left prefrontal lobe between the rs1344706 genotype and schizophrenic diagnosis, where the risk T allele carriers presented higher WM density in the schizophrenia patients and lower WM density in healthy controls in comparison with the non-risk allele carriers.2. The risk allele was associated with an increased WM density of the bilateral hippocampus in both the patients and the healthy group.

Limitation

The influence of antipsychotics to the white matter in schizophrenic patients was not fully eliminated.

Conclusions

The ZNF804A variant may confer risk for schizophrenia by exerting its effects on the WM in the left prefrontal lobe together with other risk factors for schizophrenia.     

Watching the fetal brain at ‘rest’

Functional magnetic resonance imaging (fMRI) has allowed insights into the spatiotemporal distribution of human brain networks. According to the neurophysiological property of the fetal brain to generate spontaneous activity, we aimed to determine the feasibility of investigating the maturation of intrinsic networks, beginning at gestational week 20 in healthy human fetuses by combining resting-state fMRI and an analytical approach, independent component analysis (ICA).In this study, functional images of 16 fetuses with morphologically normal brain development, from 20 to 36 gestational weeks of age, were acquired on a 1.5 T unit (Philips Medical Systems, Best, The Netherlands) using single-shot, gradient-recalled echo-planar imaging. After preprocessing (motion correction, brain extraction), images were analyzed using single-subject ICA.We visualized a bilateral occipital network and medial and lateral prefrontal activity pattern that involved the future Brodmann areas 9-11. Furthermore, there was one either predominantly right (3/7 cases) or left (4/7 cases) hemispheric lateralized network that involved the superior temporal cortical regions (Brodmann areas 22 and 39). Frequency oscillations were in the range of 0.01-0.06 Hz for all networks.This study shows that resting-state networks (RSNs) are shaped and are detectable in utero. Further investigations of resting-state measurements in the fetus may therefore allow developmental brain activity monitoring and may provide insights into early brain function.     

3.0T常规磁共振阴性药物难治性颞叶癫痫脑灰质及结构网络研究

目的探讨3.0T常规磁共振阴性的药物难治性颞叶癫痫(rTLE-N)与药物控制性颞叶癫痫(cTLE-N)脑灰质体积及脑白质结构网络拓扑属性差异。方法选取2017年3月至2019年8月在广西医科大学第一附属医院就诊的20例rTLE-N、15例cTLE-N完成头颅3DT1及DTI扫描,20例健康对照(HC)也完成此项检查。基于体素的形态学分析(VBM)方法比较3组脑灰质体积差异,基于图论的方法比较3组脑白质结构网络拓扑属性差异。结果①VBM结果:与HC组相比,rTLE-N组在双侧海马、丘脑、颞中回、内侧和旁扣带回,左侧直回、眶内额上回,右侧海马旁回灰质体积减少(P<0.001);cTLE-N组右侧颞中回、眶内额上回灰质体积减少(P<0.001)。与cTLE-N组相比,rTLE-N组在双侧岛叶、中央沟盖,左侧海马旁回、眶内额上回、梭状回、小脑6区,右侧丘脑、枕下回灰质体积减少(P<0.001);②脑白质结构网络拓扑属性结果:3组脑白质结构网络均表现出小世界属性。与HC组比较,rTLE-N组最短路径长度(Lp)增加、局部效率(Eloc)及全局效率(Eg)下降(P<0.05),cTLE-N组Lp增加、Eg下降(P<0.05);与cTLE-N组比较,rTLE-N组Lp增加、Eloc及Eg下降(P<0.05)。结论TLE-N是一种脑网络疾病,但rTLE-N与cTLE-N致痫网络不同,cTLE-N脑灰质萎缩较局限但已出现脑结构网络拓扑属性受损,而rTLE-N涉及多个脑区灰质萎缩且脑结构网络拓扑属性损害更严重。