Higher Structural Connectivity Research Articles

A spatially constrained independent component analysis jointly informed by structural and functional network connectivity

Abstract There are a growing number of neuroimaging studies motivating joint structural and functional brain connectivity. The brain connectivity of different modalities provides an insight into brain functional organization by leveraging complementary information, especially for brain disorders such as schizophrenia. In this paper, we propose a multimodal independent component analysis (ICA) model that utilizes information from both structural and functional brain connectivity guided by spatial maps to estimate intrinsic connectivity networks (ICNs). Structural connectivity is estimated through whole-brain tractography on diffusion-weighted MRI (dMRI), while functional connectivity is derived from resting-state functional MRI (rs-fMRI). The proposed structural-functional connectivity and spatially constrained ICA (sfCICA) model estimates ICNs at the subject level using a multiobjective optimization framework. We evaluated our model using synthetic and real datasets (including dMRI and rs-fMRI from 149 schizophrenia patients and 162 controls). Multimodal ICNs revealed enhanced functional coupling between ICNs with higher structural connectivity, improved modularity, and network distinction, particularly in schizophrenia. Statistical analysis of group differences showed more significant differences in the proposed model compared with the unimodal model. In summary, the sfCICA model showed benefits from being jointly informed by structural and functional connectivity. These findings suggest advantages in simultaneously learning effectively and enhancing connectivity estimates using structural connectivity.

Cerebral blood flow and structural connectivity after working memory or physical training in paediatric cancer survivors – Exploratory findings

ABSTRACT Paediatric cancer survivors often suffer from cognitive long-term difficulties. Consequently, strengthening cognition is of major clinical relevance. This study investigated cerebral changes in relation to cognition in non-brain tumour paediatric cancer survivors after working memory or physical training compared to a control group. Thirty-four children (≥one-year post-treatment) either underwent eight weeks of working memory training (n = 10), physical training (n = 11), or a waiting period (n = 13). Cognition and MRI, including arterial spin labelling and diffusion tensor imaging, were assessed at three time points (baseline, post-training, and three-month follow-up). Results show lower cerebral blood flow immediately after working memory training (z = −2.073, p = .038) and higher structural connectivity at the three-month follow-up (z = −2.240, p = .025). No cerebral changes occurred after physical training. Short-term changes in cerebral blood flow correlated with short-term changes in cognitive flexibility (r = −.667, p = .049), while long-term changes in structural connectivity correlated with long-term changes in working memory (r = .786, p = .021). Despite the caution given when interpreting data from small samples, this study suggests a link between working memory training and neurophysiological changes. Further research is needed to validate these findings.

A spatially constrained independent component analysis jointly informed by structural and functional network connectivity.

There are a growing number of neuroimaging studies motivating joint structural and functional brain connectivity. Brain connectivity of different modalities provides insight into brain functional organization by leveraging complementary information, especially for brain disorders such as schizophrenia. In this paper, we propose a multi-modal independent component analysis (ICA) model that utilizes information from both structural and functional brain connectivity guided by spatial maps to estimate intrinsic connectivity networks (ICNs). Structural connectivity is estimated through whole-brain tractography on diffusion-weighted MRI (dMRI), while functional connectivity is derived from resting-state functional MRI (rs-fMRI). The proposed structural-functional connectivity and spatially constrained ICA (sfCICA) model estimates ICNs at the subject level using a multi-objective optimization framework. We evaluated our model using synthetic and real datasets (including dMRI and rs-fMRI from 149 schizophrenia patients and 162 controls). Multi-modal ICNs revealed enhanced functional coupling between ICNs with higher structural connectivity, improved modularity, and network distinction, particularly in schizophrenia. Statistical analysis of group differences showed more significant differences in the proposed model compared to the unimodal model. In summary, the sfCICA model showed benefits from being jointly informed by structural and functional connectivity. These findings suggest advantages in simultaneously learning effectively and enhancing connectivity estimates using structural connectivity.

THE ASSOCIATIONS OF SOCIOECONOMIC POSITION WITH STRUCTURAL BRAIN DAMAGE AND CONNECTIVITY AND COGNITION

Abstract Socioeconomic inequalities in the risk for cognitive impairment have been reported, which might partly act through structural brain damage and connectivity. This study investigated the extent to which the association of early-life socioeconomic position (SEP) with later-life cognitive performance is mediated by later-life SEP, and whether the association of SEP with later-life cognitive performance can be explained by structural brain damage and connectivity. We used cross-sectional data from the population-based Maastricht study (n=4,839; mean age 59.2±8.7 years, 49.8% women). Early-life SEP was assessed retrospectively by self-reported poverty and parental education. Later-life SEP included education, occupation, and household income. Participants underwent cognitive testing and 3 T magnetic resonance imaging to measure volumes of white matter hyperintensities, gray matter, white matter, cerebrospinal fluid, and structural connectivity. Multiple linear regression analyses tested the associations between SEP, MRI brain markers and cognition. Structural equation modeling tested mediation. Results indicated that higher SEP was associated with higher grey matter volume, lower white matter volume, and higher structural connectivity. Structural brain damage and lower structural connectivity were associated with lower cognition. Both higher early-life and later-life SEP were associated with higher cognition. The association of early-life SEP with later-life cognition was partly mediated by later-life SES (73.8%). However, the extent to which the association of SEP with cognition could be explained by structural brain damage or connectivity was marginal (up to 5.9%). More research is needed to investigate alternative pathways that can explain the associations between SEP with later-life cognition.

The associations of socioeconomic status with structural brain damage and connectivity and cognition: The Maastricht Study

AbstractBackgroundSocioeconomic inequalities in the risk for cognitive impairment have been reported, which might partly act through structural brain damage or differential numbers of brain connections (structural connectivity). This study investigated the extent to which the association of early‐life socioeconomic status (SES) with later‐life cognitive performance is mediated by later‐life SES, and whether the association of SES with later‐life cognitive performance can be explained by structural brain damage and connectivity.MethodWe used cross‐sectional data from the population‐based Maastricht study (n = 4,839; mean age 59.2±8.7 years, 49.8% women). Early‐life SES was assessed retrospectively by self‐reported poverty and parental education. Later‐life SES included education, occupation, and household income. Participants underwent cognitive testing and 3 T magnetic resonance imaging to measure volumes of white matter hyperintensities, gray matter, white matter, cerebrospinal fluid, and structural connectivity. Multiple linear regression analyses tested the associations between SES, brain markers and cognition. Analyses were adjusted for age, sex, and type 2 diabetes (because of oversampling). Structural equation modeling tested mediation.ResultHigher SES was associated with higher grey matter volume, lower white matter volume, and higher structural connectivity. Structural brain damage and lower structural connectivity were associated with lower overall cognitive performance. Both higher early‐life and later‐life SES were associated with overall higher cognitive performance (B [95% CI] medium versus low early‐life SES = 0.17[0.12;0.23]; B high versus low early‐life SES = 0.26[0.20;0.32]; B medium versus low later‐life SES = 0.46[0.41;0.52]; B high versus low later‐life SES = 0.72[0.67;0.78]). The association of early‐life SES with later‐life cognitive performance was partly mediated by later‐life SES (73.8%). The extent to which the association of SES with cognitive performance could be explained by structural brain damage or connectivity was marginal (up to 5.9%).ConclusionThough there was an association between early‐life SES and later‐life cognitive performance independent of later‐life SES, a large part of this association could be explained by later‐life SES. Structural brain damage and connectivity marginally explained socioeconomic inequalities in cognitive performance. More research is needed to investigate alternative pathways that explain associations of life‐course SES with later‐life cognition.

Recovery of Supraspinal Microstructural Integrity and Connectivity in Patients Undergoing Surgery for Degenerative Cervical Myelopathy.

It remains unknown if the progressive loss of axonal conduction along sensorimotor tracts can be recovered after surgery in patients with degenerative cervical myelopathy (DCM) and if subsequent adaptive microstructural changes are associated with the neurological improvement. To investigate the upstream recovery of microstructural integrity and reorganization of microstructural connectivity that occurs in patients with DCM after surgical decompression. Preoperative and postoperative cerebral diffusion tensor imaging and diffusion spectrum imaging data were collected for 22 patients with DCM (age = 56.9 ± 9.1 years). Paired t-tests were used to identify significant microstructural changes within cohorts, and correlation analysis was used to identify whether those changes are associated with neurological improvement. Before surgery, higher structural connectivity (SC) was observed in the prefrontal/frontal lobes, anterior cingulate, the internal and external capsules, and the anterior, posterior, and superior regions of the corona radiata fibers. Following surgery, an increased modified Japanese Orthopaedic Association score was associated with increased SC from the primary sensorimotor regions to the posterior cingulate and precuneus; increased SC between the cerebellum and the bilateral lingual gyri; and decreased SC from areas of the limbic system to the basal ganglia and the frontal lobe. In addition, increased fractional anisotropy and normalized quantitative anisotropy values along white matter fibers responsible for conveying sensory information and motor coordination and planning were associated with neurological improvement of patients with DCM after surgery. Recovery of microstructural integrity along the corticospinal tract and other sensorimotor pathways, together with supraspinal reorganization of microstructural connectivity within sensory and motor-related regions, was associated with neurological improvement after surgical decompression.

Functional redundancy of the premotor network in hemispherotomy patients.

ObjectiveUsing multimodal imaging, we tested the hypothesis that patients after hemispherotomy recruit non‐primary motor areas and non‐pyramidal descending motor fibers to restore motor function of the impaired limb.MethodsFunctional and structural MRI data were acquired in a group of 25 patients who had undergone hemispherotomy and in a matched group of healthy controls. Patients’ motor impairment was measured using the Fugl‐Meyer Motor Assessment. Cortical areas governing upper extremity motor‐control were identified by task‐based functional MRI. The resulting areas were used as nodes for functional and structural connectivity analyses.ResultsIn hemispherotomy patients, movement of the impaired upper extremity was associated to widespread activation of non‐primary premotor areas, whereas movement of the unimpaired one and of the control group related to activations prevalently located in the primary motor cortex (all p ≤ 0.05, FWE‐corrected). Non‐pyramidal tracts originating in premotor/supplementary motor areas and descending through the pontine tegmentum showed relatively higher structural connectivity in patients (p < 0.001, FWE‐corrected). Significant correlations between structural connectivity and motor impairment were found for non‐pyramidal (p = 0.023, FWE‐corrected), but not for pyramidal connections.InterpretationA premotor/supplementary motor network and non‐pyramidal fibers seem to mediate motor function in patients after hemispherotomy. In case of hemispheric lesion, the homologous regions in the contralesional hemisphere may not compensate the resulting motor deficit, but the functionally redundant premotor network.

Enhanced structural connectivity within the motor loop in professional boxers prior to a match

Professional boxers train to reduce their body mass before a match to refine their body movements. To test the hypothesis that the well-defined movements of boxers are represented within the motor loop (cortico-striatal circuit), we first elucidated the brain structure and functional connectivity specific to boxers and then investigated plasticity in relation to boxing matches. We recruited 21 male boxers 1 month before a match (Time1) and compared them to 22 age-, sex-, and body mass index (BMI)-matched controls. Boxers were longitudinally followed up within 1 week prior to the match (Time2) and 1 month after the match (Time3). The BMIs of boxers significantly decreased at Time2 compared with those at Time1 and Time3. Compared to controls, boxers presented significantly higher gray matter volume in the left putamen, a critical region representing motor skill training. Boxers presented significantly higher functional connectivity than controls between the left primary motor cortex (M1) and left putamen, which is an essential region for establishing well-defined movements. Boxers also showed significantly higher structural connectivity in the same region within the motor loop from Time1 to Time2 than during other periods, which may represent the refined movements of their body induced by training for the match.

The effect of sex and age on cortical grey and white matter volumes of frontal lobe

Grey matter (GM) of the frontal lobe carries out its complex function such as muscle control, speech, decision making, and self-control; while the white matter (WM) of frontal lobe is a major contributor to human brain enlargement and higher structural connectivity. This study was conducted to assess the effect of sex and age on grey and white matter volumes (GMV and WMV) of the frontal lobe and its gyri in healthy young adult Sudanese. The present study included 139 healthy Sudanese subjects (80 males and 59 females). Participant’s ages were ranging between 20-40 years. T1-weighted MR brain images with thickness 1mm were obtained. MR images of the subjects were analyzed using the automatic segmentation software (BrainSuite). GMV and WMV of frontal lobe and its gyri were estimated using the output data of the process of software. Males had greater GMV and WMV of the frontal lobes (251.18±31.80cm3 and 143.48±22.92cm3, respectively) and most of frontal lobe gyri (P&lt;0.05). Change with age in GMV has been reported in the frontal lobes, superior frontal gyrus, pars orbitalis, orbitofrontal, and cingulate gyrus (P&lt;0.05). Change with age in WM volumes has been found in the cingulate, precentral, and paracentral gyri (P&lt;0.05). Sex has prominent effect on GMV and WMV of the frontal lobes and most of frontal lobe gyri, thus sex is a major contributor to GMV and WMV differences between individuals. Age effect GMV and WMV of most frontal lobe gyri, these findings confirm the continuation of maturation of frontal lobe until fourth decade. Assessing effect of sex and age on GM and WM in healthy adult has major importance to distinguish the normal brain from diseased.

Higher structural connectivity and resistance against invasions of soil bioengineering over hard-engineering for riverbank stabilisation

Riparian corridors play an important role for the maintenance of regional biodiversity and ecosystem functions. Riparian forests are even the only semi-natural vegetation strips remaining in many agricultural or urbanised landscapes. In such landscapes, the spatial continuity of riparian vegetation is frequently broken by the construction of stabilisation structures engineered for erosion control. Here, we examined the effects of different riverbank stabilisation structures—fascines (soil bioengineering), ripraps (hard engineering), and mixed-technique (lower-bank ripraps with upper-bank plantings)—on the structural connectivity of their respective riverbanks. We first revisited previously studied stabilisation structures to extend their vegetation sampling to their adjacent riverbanks. Then, for each type of stabilisation structure, we compared community composition, richness and abundance of native and invasive alien species (IAS), and cover of vegetation strata (herbaceous, shrub and tree) between stabilised embankments and their upstream and downstream banks. Results indicated that, although the composition of fascine banks differed from that of their adjacent riverbanks, they fitted nicely in the structural continuity of their riparian surroundings. Differences were likely explained by the proportion of fast-growing woody species (e.g. willows) planted in fascines, which also induced strong reductions in IAS richness and abundances; i.e. propagule “sinks”. Conversely, ripraps broke the structural continuity of riverbanks and were heavily dominated by IAS while mixed-technique banks displayed intermediate characteristics. Consequently, we argued that fascines may be the riverbank stabilisation structures displaying highest ecological benefits in terms of habitat quality and connectivity and should be preferred over the other investigated engineering techniques.

Higher Adherence to the Mediterranean Diet Is Associated With Preserved White Matter Integrity and Altered Structural Connectivity.

The Mediterranean diet (MedDiet) has been associated with cognitive performance. Yet, controlled trials have yielded contradictory results. To tackle this controversy, a comprehensive multimodal analysis of the association of the MedDiet with cognitive performance and brain structure in normative aging is still necessary. Here, community dwellers ≥50 years from a cohort study on normative aging (n = 76) underwent a (i) magnetic resonance imaging session with two acquisitions: structural and diffusion-weighted imaging (DWI); (ii) neuropsychological battery of tests focusing on memory and executive functioning; and (iii) dietary assessment through the Mediterranean Diet Assessment Screener (MEDAS, score range: 0–14, scores ≥10 indicate high adherence to the Mediterranean diet) 18 months prior to the brain imaging and neuropsychological assessment. We found that high adherence to the MedDiet (MEDAS ≥10) was associated with higher values of fractional anisotropy and lower diffusivity values in the brain white matter. Similarly, high adherence to the MedDiet was associated with higher structural connectivity between left hemisphere brain regions. Specifically, the amygdala, lingual, olfactory, middle occipital gyrus, and calcarine areas. No association was found between high adherence to the MedDiet and total brain volumes or hypointensities. Higher adherence to the MedDiet was positively associated with executive functioning scores. These results suggest that high adherence to the MedDiet positively associates with brain health, specifically with executive function scores and white matter integrity of bundles related to the processing and integration of taste, reward, and decision making. These findings seem to support the view that the MedDiet should be part of recommendations to promote a healthy brain.

Awareness of Emotional Stimuli Determines the Behavioral Consequences of Amygdala Activation and Amygdala-Prefrontal Connectivity.

Conscious awareness of negative cues is thought to enhance emotion-regulatory capacity, but the neural mechanisms underlying this effect are unknown. Using continuous flash suppression (CFS) in the MRI scanner, we manipulated visual awareness of fearful faces during an affect misattribution paradigm, in which preferences for neutral objects can be biased by the valence of a previously presented stimulus. The amygdala responded to fearful faces independently of awareness. However, when awareness of fearful faces was prevented, individuals with greater amygdala responses displayed a negative bias toward unrelated novel neutral faces. In contrast, during the aware condition, inverse coupling between the amygdala and prefrontal cortex reduced this bias, particularly among individuals with higher structural connectivity in the major white matter pathway connecting the prefrontal cortex and amygdala. Collectively, these results indicate that awareness promotes the function of a critical emotion-regulatory network targeting the amygdala, providing a mechanistic account for the role of awareness in emotion regulation.

Psychopathic traits in adolescents are associated with higher structural connectivity

Altered structural connectivity has been reported in antisocial juveniles, but findings have been inconsistent. Given the phenotypical heterogeneity among individuals showing antisocial behavior, specification of the association between structural connectivity and the dimensions of psychopathic traits (i.e., callous-unemotional, grandiose-manipulative, and impulsive–irresponsible traits) may aid in more reliably elucidating the neural mechanisms underlying antisocial behavior during adolescence. In this study, a sample of 145 adolescents (mean age 17.6, SD 1.6) from a childhood arrestee cohort participated in a neuroimaging protocol including diffusion tensor imaging (DTI). Fractional anisotropy (FA), radial diffusivity (RD) and axial diffusivity (AD), as obtained by tract-based spatial statistics, were associated with juveniles' scores on the Youth Psychopathic Traits Inventory. Grandiose-manipulative traits were positively associated with FA and negatively with RD in a wide range of white matter tracts, suggesting abnormal myelination related to these traits. Callous-unemotional traits were positively associated with FA and AD in specific white matter tracts, including the corpus callosum and corticospinal tract. The differential associations between dimensions of psychopathic traits and measures of structural connectivity support the notion that multiple distinct neural mechanisms underlie antisocial and psychopathic development.

Long-term effects of marijuana use on the brain.

Questions surrounding the effects of chronic marijuana use on brain structure continue to increase. To date, however, findings remain inconclusive. In this comprehensive study that aimed to characterize brain alterations associated with chronic marijuana use, we measured gray matter (GM) volume via structural MRI across the whole brain by using voxel-based morphology, synchrony among abnormal GM regions during resting state via functional connectivity MRI, and white matter integrity (i.e., structural connectivity) between the abnormal GM regions via diffusion tensor imaging in 48 marijuana users and 62 age- and sex-matched nonusing controls. The results showed that compared with controls, marijuana users had significantly less bilateral orbitofrontal gyri volume, higher functional connectivity in the orbitofrontal cortex (OFC) network, and higher structural connectivity in tracts that innervate the OFC (forceps minor) as measured by fractional anisotropy (FA). Increased OFC functional connectivity in marijuana users was associated with earlier age of onset. Lastly, a quadratic trend was observed suggesting that the FA of the forceps minor tract initially increased following regular marijuana use but decreased with protracted regular use. This pattern may indicate differential effects of initial and chronic marijuana use that may reflect complex neuroadaptive processes in response to marijuana use. Despite the observed age of onset effects, longitudinal studies are needed to determine causality of these effects.

Response of an ecological indicator to landscape composition and structure: Implications for functional units of temperate rainforest ecosystems

We evaluated the northern flying squirrel (Glaucomys sabrinus griseifrons), a known associate of key habitat features and processes of old-growth forest, for its capacity as a broad-scale ecological indicator of temperate rainforest ecosystem condition in southeastern Alaska, USA. We utilized a spatially explicit, resource-selection function to evaluate its distribution relative to landscape composition and structure at local (within home-range) and broad (home-range selection) spatial scales, followed by a moving-window analysis to model patch occupancy across this landscape. We found strong support for the influence of type, size, and compositional elements: large, old-growth patches were selected at both spatial scales, and regenerating forest patches ≤40yrs old were selected against at the broader scale. More importantly, we found that occupancy was related to critical thresholds in composition: patches required ≥73% old-growth forest cover or a minimum total area of 73ha of old-growth forest to be occupied by flying squirrels. A non-uniform pattern of selection for patches with higher structural connectivity at the local scale, but not at the broader scale, was likely a result of the “empty forest” phenomenon, in which remnant patches were inaccessible in this fragmented landscape. These results are consistent with recent studies of this and related species and suggest that occurrence of northern flying squirrels in southeastern Alaska is influenced by a number of landscape structure and compositional variables that relate critically to late-seral forest conditions. These findings shed new light on the utility of this species as an ecological indicator and its functional relevance to the resilience of fragmented forest ecosystems.

Frontal white matter volume is associated with brain enlargement and higher structural connectivity in anthropoid primates.

Previous research has indicated the importance of the frontal lobe and its ‘executive’ connections to other brain structures as crucial in explaining primate neocortical adaptations. However, a representative sample of volumetric measurements of frontal connective tissue (white matter) has not been available. In this study, we present new volumetric measurements of white and grey matter in the frontal and non-frontal neocortical lobes from 18 anthropoid species. We analyze this data in the context of existing theories of neocortex, frontal lobe and white versus grey matter hyperscaling. Results indicate that the ‘universal scaling law’ of neocortical white to grey matter applies separately for frontal and non-frontal lobes; that hyperscaling of both neocortex and frontal lobe to rest of brain is mainly due to frontal white matter; and that changes in frontal (but not non-frontal) white matter volume are associated with changes in rest of brain and basal ganglia, a group of subcortical nuclei functionally linked to ‘executive control’. Results suggest a central role for frontal white matter in explaining neocortex and frontal lobe hyperscaling, brain size variation and higher neural structural connectivity in anthropoids.