Diffusion tensor imaging study of white matter fiber tracts in pediatric bipolar disorder and attention-deficit/hyperactivity disorder

White matter alterations in Attention-Deficit/Hyperactivity Disorder (ADHD): a systematic review of 129 diffusion imaging studies with meta-analysis

Aberrant anatomical brain connections in attention-deficit/hyperactivity disorder (ADHD) are reported inconsistently across diffusion weighted imaging (DWI) studies. Based on a pre-registered protocol (Prospero: CRD42021259192), we searched PubMed, Ovid, and Web of Knowledge until 26/03/2022 to conduct a systematic review of DWI studies. We performed a quality assessment based on imaging acquisition, preprocessing, and analysis. Using signed differential mapping, we meta-analyzed a subset of the retrieved studies amenable to quantitative evidence synthesis, i.e., tract-based spatial statistics (TBSS) studies, in individuals of any age and, separately, in children, adults, and high-quality datasets. Finally, we conducted meta-regressions to test the effect of age, sex, and medication-naïvety. We included 129 studies (6739 ADHD participants and 6476 controls), of which 25 TBSS studies provided peak coordinates for case-control differences in fractional anisotropy (FA)(32 datasets) and 18 in mean diffusivity (MD)(23 datasets). The systematic review highlighted white matter alterations (especially reduced FA) in projection, commissural and association pathways of individuals with ADHD, which were associated with symptom severity and cognitive deficits. The meta-analysis showed a consistent reduced FA in the splenium and body of the corpus callosum, extending to the cingulum. Lower FA was related to older age, and case-control differences did not survive in the pediatric meta-analysis. About 68% of studies were of low quality, mainly due to acquisitions with non-isotropic voxels or lack of motion correction; and the sensitivity analysis in high-quality datasets yielded no significant results. Findings suggest prominent alterations in posterior interhemispheric connections subserving cognitive and motor functions affected in ADHD, although these might be influenced by non-optimal acquisition parameters/preprocessing. Absence of findings in children may be related to the late development of callosal fibers, which may enhance case-control differences in adulthood. Clinicodemographic and methodological differences were major barriers to consistency and comparability among studies, and should be addressed in future investigations.

Regional microstructural differences in ADHD youth with and without a family history of bipolar I disorder

BACKGROUND

Having a first-degree relative with bipolar I disorder (BD) in conjunction with prodromal attention deficit/hyperactivity disorder (ADHD) may represent a unique phenotype that confers greater risk for developing BD than ADHD alone. However, underlying neuropathoetiological mechanisms remain poorly understood. This cross-sectional study compared regional microstructure in psychostimulant-free ADHD youth with ('high-risk', HR) and without ('low-risk', LR) a first-degree relative with BD, and healthy controls (HC).

METHODS

A total of 140 (high-risk, n = 44; low-risk, n = 49; and HC, n = 47) youth (mean age: 14.1 ± 2.5 years, 65 % male) were included in the analysis. Diffusion tensor images were collected and fractional anisotropy (FA) and mean diffusivity (MD) maps were calculated. Both tract-based and voxel-based analyses were performed. Correlations between clinical ratings and microstructural metrics that differed among groups were examined.

RESULTS

No significant group differences in major long-distance fiber tracts were observed. The high-risk ADHD group exhibited predominantly higher FA and lower MD in frontal, limbic, and striatal subregions compared with the low-risk ADHD group. Both low-risk and high-risk ADHD groups exhibited higher FA in unique and overlapping regions compared with HC subjects. Significant correlations between regional microstructural metrics and clinical ratings were observed in ADHD groups.

LIMITATIONS

Prospective longitudinal studies will be required to determine the relevance of these findings to BD risk progression.

CONCLUSIONS

Psychostimulant-free ADHD youth with a BD family history exhibit different microstructure alterations in frontal, limbic, and striatal regions compared with ADHD youth without a BD family history, and may therefore represent a unique phenotype relevant to BD risk progression.

Shared and distinct white matter abnormalities in adolescent-onset schizophrenia and adolescent-onset psychotic bipolar disorder

BACKGROUND

While adolescent-onset schizophrenia (ADO-SCZ) and adolescent-onset bipolar disorder with psychosis (psychotic ADO-BPD) present a more severe clinical course than their adult forms, their pathophysiology is poorly understood. Here, we study potentially state- and trait-related white matter diffusion-weighted magnetic resonance imaging (dMRI) abnormalities along the adolescent-onset psychosis continuum to address this need.

METHODS

Forty-eight individuals with ADO-SCZ (20 female/28 male), 15 individuals with psychotic ADO-BPD (7 female/8 male), and 35 healthy controls (HCs, 18 female/17 male) underwent dMRI and clinical assessments. Maps of extracellular free-water (FW) and fractional anisotropy of cellular tissue (FAT) were compared between individuals with psychosis and HCs using tract-based spatial statistics and FSL's Randomise. FAT and FW values were extracted, averaged across all voxels that demonstrated group differences, and then utilized to test for the influence of age, medication, age of onset, duration of illness, symptom severity, and intelligence.

RESULTS

Individuals with adolescent-onset psychosis exhibited pronounced FW and FAT abnormalities compared to HCs. FAT reductions were spatially more widespread in ADO-SCZ. FW increases, however, were only present in psychotic ADO-BPD. In HCs, but not in individuals with adolescent-onset psychosis, FAT was positively related to age.

CONCLUSIONS

We observe evidence for cellular (FAT) and extracellular (FW) white matter abnormalities in adolescent-onset psychosis. Although cellular white matter abnormalities were more prominent in ADO-SCZ, such alterations may reflect a shared trait, i.e. neurodevelopmental pathology, present across the psychosis spectrum. Extracellular abnormalities were evident in psychotic ADO-BPD, potentially indicating a more dynamic, state-dependent brain reaction to psychosis.

The anatomical networks based on probabilistic structurally connectivity in bipolar disorder across mania, depression, and euthymic states

BACKGROUNDS

There have pieces of evidence of the distinct aberrant functional network topology profile in bipolar disorder (BD) across mania, depression, and euthymic episodes. However, the underlying anatomical network topology pattern in BD across different episodes is unclear.

METHODS

We calculated the whole-brain probabilistic structurally connectivity across 143 subjects (72 with BD [34 depression; 13 mania; 25 euthymic] and 53 healthy controls), and used graph theory to examine the trait- and state-related topology alterations of the structural connectome in BD. The correlation analysis was further conducted to explore the relationship between detected network measures and clinical symptoms.

RESULTS

There no omnibus alteration of any global network metrics were observed across all diagnostic groups. In the regional network metrics level, bipolar depression showed increased clustering coefficient in the right lingual gyrus compared with all other groups, and the increased clustering coefficient in the right lingual gyrus positively correlated with depression, anxiety, and illness burden symptoms but negatively correlated with mania symptoms; manic and euthymic patients showed decreased clustering coefficient in the left inferior occipital gyrus compared with HCs.

LIMITATIONS

The moderate sample size of all patient groups (especially for subjects with mania) might have contributed to the negative findings of the trait feature in this study.

CONCLUSIONS

We demonstrated the altered regional connectivity pattern in the occipital lobe of the bipolar depression and mania episode, especially the lingual gyrus. The association of the clustering coefficient in the lingual gyrus with clinical symptoms helps monitor the state of BD.

Is structural connectivity different in child and adolescent relatives of patients with bipolar disorder? A narrative review according to studies with DTI

INTRODUCTION

Bipolar disorder (BD) has been associated with a decrease in white matter integrity. Diffusion tensor imaging (DTI) studies have enabled these changes to be elucidated with higher quality. Due to BD's high heritability, some studies have been conducted in relatives of BD patients looking at white matter integrity, and have found that structural connectivity may also be affected. This alteration has been proposed as a potential BD biomarker of vulnerability. However, there are few studies in children and adolescents.

OBJECTIVE

To conduct a review of the literature on changes in white matter integrity determined by DTI in high-risk children and adolescents.

RESULTS

Brain structural connectivity in the paediatric population is described in studies using DTI. Changes in the myelination process from its evolution within normal neurodevelopment to the findings in fractional anisotropy (FA) in BD patients and their high-risk relatives are also described.

CONCLUSIONS

Studies show that both BD patients and their at-risk relatives present a decrease in FA in specific brain regions. Studies in children and adolescents with a high risk of BD, indicate a reduced FA in axonal tracts involved in emotional and cognitive functions. Decreased FA can be considered as a vulnerability biomarker for BD.

A fatal alliance: Glial connexins, myelin pathology and mental disorders

Mature oligodendrocytes are myelin forming glial cells which are responsible for myelination of neuronal axons in the white matter of the central nervous system. Myelin pathology is a major feature of severe neurological disorders. Oligodendrocyte-specific gene mutations and/or white matter alterations have also been addressed in a variety of mental disorders. Breakdown of myelin integrity and demyelination is associated with severe symptoms, including impairments in motor coordination, breathing, dysarthria, perception (vision and hearing), and cognition. Furthermore, there is evidence indicating that myelin sheath defects and white matter pathology contributes to the affective and cognitive symptoms of patients with mental disorders. Oligodendrocytes express the connexins GJC2; mCx47 [human (GJC2) and mouse (mCx47) connexin gene nomenclature according to Söhl and Willecke (2003)], GJB1; mCx32, and GJD1; mCx29 in both white and gray matter. Preclinical findings indicate that alterations in connexin expression in oligodendrocytes and astrocytes can induce myelin defects. GJC2; mCx47 is expressed at early embryonic stages in oligodendrocyte precursors cells which precedes central nervous system myelination. In adult humans and animals GJC2, respectively mCx47 expression is essential for oligodendrocyte function and ensures adequate myelination as well as myelin maintenance in the central nervous system. In the past decade, evidence has accumulated suggesting that mental disorders can be accompanied by changes in connexin expression, myelin sheath defects and corresponding white matter alterations. This dual pathology could compromise inter-neuronal information transfer, processing and communication and eventually contribute to behavioral, sensory-motor, affective and cognitive symptoms in patients with mental disorders. The induction of myelin repair and remyelination in the central nervous system of patients with mental disorders could help to restore normal neuronal information propagation and ameliorate behavioral and cognitive symptoms in individuals with mental disorders.

Disrupted white matter microstructure correlates with impulsivity in children and adolescents with bipolar disorder

Altered white matter (WM) microstructure likely occurs in children with bipolar disorder (BD) with impulsivity representing one of the core features. However, altered WM microstructures and their age-related trendlines in children with BD and those at high-risk of developing BD, as well as correlations of WM microstructures with impulsivity, have been poorly investigated. In this study, diffusion MRI, cognitive, and impulsivity assessments were obtained from children/adolescents diagnosed with BD, offspring of individuals with BD (high-risk BD) and age-matched healthy controls. A novel atlas-based WM skeleton measurement approach was used to quantify WM microstructural integrity with all diffusion-tensor-imaging (DTI) metrics including fractional anisotropy, axial, mean and radial diffusivity to survey entire WM tracts and ameliorate partial volume effects. Among all DTI-derived metric measures, radial diffusivity quantifying WM myelination was found significantly higher primarily in corpus callosum and in the corona radiata in children with BD compared to controls. Distinguished from age-related progressively decreasing diffusivities and increasing fractional anisotropy in healthy controls, flattened age-related trendlines were found in BD group, and intermediate developmental rates were observed in high-risk group. Larger radial diffusivity in the corpus callosum and corona radiata significantly correlated with shorter response times to affective words that indicate higher impulsivity in the BD group, whereas no such correlation was found in the healthy control group. This work corroborates the progressive nature of pediatric BD and suggests that WM microstructural disruption involved in affective regulation and sensitive to impulsivity may serve as a biomarker of pediatric BD progression.

Does the Brain Matter? Cortical Alterations in Pediatric Bipolar Disorder: A Critical Review of Structural and Functional Magnetic Resonance Studies

Pediatric bipolar disorder (PBD) is associated with significant psychosocial impairment, high use of mental health services and a high number of relapses and hospitalization. Neuroimaging techniques provide the opportunity to study the neurodevelopmental processes underlying PBD, helping to identify the endophenotypic markers of illness and early biological markers of PBD. The aim of the study is to review available studies assessing structural and functional brain correlates associated with PBD. PubMed, ISI Web of Knowledge and PsychINFO databases have been searched. Studies were included if they enrolled patients aged 0-18 years with a main diagnosis of PBD according to ICD or DSM made by a mental health professional, adopted structural and/or functional magnetic resonance as the main neuroimaging method, were written in English and included a comparison with healthy subjects. Of the 400 identified articles, 46 papers were included. Patients with PBD present functional and anatomic alterations in structures normally affecting regulations and cognition. Structural neuroimaging revealed a significant reduction in gray matter, with cortical thinning in bilateral frontal, parietal and occipital cortices. Functional neuroimaging studies reported a reduced engagement of the frontolimbic and hyperactivation of the frontostriatal circuitry. Available studies on brain connectivity in PBD patients potentially indicate less efficient connections between regions involved in cognitive and emotional functions. A greater functional definition of alteration in brain functioning of PBD patients will be useful to set up a developmentally sensitive targeted pharmacological and nonpharmacological intervention.

Association between attention-deficit/hyperactivity disorder symptom severity and white matter integrity moderated by in-scanner head motion

Attention-deficit/hyperactivity disorder (ADHD) is a common and debilitating neurodevelopmental disorder associated with various negative life impacts. The manifestation of ADHD is very heterogeneous, and previous investigations on neuroanatomical alterations in ADHD have yielded inconsistent results. We investigated the mediating effect of in-scanner head motion and ADHD hyperactivity severity on motion-corrected fractional anisotropy (FA) using diffusion tensor imaging in the currently largest sample (n = 739) of medication-naïve children and adolescents (age range 5-22 years). We used automated tractography to examine whole-brain and mean FA of the tracts most frequently reported in ADHD; corpus callosum forceps major and forceps minor, left and right superior-longitudinal fasciculus, and left and right corticospinal tract (CST). Associations between FA and hyperactivity severity appeared when in-scanner head motion was not accounted for as mediator. However, causal mediation analysis revealed that these effects are fully mediated through in-scanner head motion for whole-brain FA, the corpus callosum forceps minor, and left superior-longitudinal fasciculus. Direct effect of hyperactivity severity on FA was only found for the left CST. This study illustrates the crucial role of in-scanner head motion in the identification of white matter integrity alterations in ADHD and shows how neglecting irremediable motion artifacts causes spurious findings. When the mediating effect of in-scanner head motion on FA is accounted for, an association between hyperactivity severity and FA is only present for the left CST; this may play a crucial role in the manifestation of hyperactivity and impulsivity symptoms in ADHD.

Neuroprotection in late life attention-deficit/hyperactivity disorder: A review of pharmacotherapy and phenotype across the lifespan

For decades, psychostimulants have been the gold standard pharmaceutical treatment for attention-deficit/hyperactivity disorder (ADHD). In the United States, an astounding 9% of all boys and 4% of girls will be prescribed stimulant drugs at some point during their childhood. Recent meta-analyses have revealed that individuals with ADHD have reduced brain volume loss later in life (>60 y.o.) compared to the normal aging brain, which suggests that either ADHD or its treatment may be neuroprotective. Crucially, these neuroprotective effects were significant in brain regions (e.g., hippocampus, amygdala) where severe volume loss is linked to cognitive impairment and Alzheimer's disease. Historically, the ADHD diagnosis and its pharmacotherapy came about nearly simultaneously, making it difficult to evaluate their effects in isolation. Certain evidence suggests that psychostimulants may normalize structural brain changes typically observed in the ADHD brain. If ADHD itself is neuroprotective, perhaps exercising the brain, then psychostimulants may not be recommended across the lifespan. Alternatively, if stimulant drugs are neuroprotective, then this class of medications may warrant further investigation for their therapeutic effects. Here, we take a bottom-up holistic approach to review the psychopharmacology of ADHD in the context of recent models of attention. We suggest that future studies are greatly needed to better appreciate the interactions amongst an ADHD diagnosis, stimulant treatment across the lifespan, and structure-function alterations in the aging brain.

Structural white matter characteristics for working memory and switching/inhibition in children with reading difficulties: The role of the left superior longitudinal fasciculus

Reading difficulties (RDs) are characterized by slow and inaccurate reading as well as additional challenges in cognitive control (i.e., executive functions, especially in working memory, inhibition, and visual attention). Despite evidence demonstrating differences in these readers' language and visual processing abilities, white matter differences associated with executive functions (EFs) difficulties in children with RDs are scarce. Structural correlates for reading and EFs in 8- to 12-year-old children with RDs versus typical readers (TRs) were examined using diffusion tensor imaging (DTI) data. Results suggest that children with RDs showed significantly lower reading and EF abilities versus TRs. Lower fractional anisotropy (FA) in left temporo-parietal tracts was found in children with RDs, who also showed positive correlations between reading and working memory and switching/inhibition scores and FA in the left superior longitudinal fasciculus (SLF). FA in the left SLF predicted working memory performance mediated by reading ability in children with RDs but not TRs. Our findings support alterations in white matter tracts related to working memory, switching/inhibition, and overall EF challenges in children with RDs and the linkage between working memory difficulties and FA alterations in the left SLF in children with RDs via reading.

White matter microstructure in children and adolescents with ADHD

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A systematic review of diffusion MRI studies in children and adolescents with ADHD.

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46 studies included, encompassing multiple diffusion MRI techniques.

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Reduced white matter microstructure was reported in several studies.

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Mixed evidence linking white matter differences with specific cognitive processes.

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Common limitations included sample size, head motion and medication status.

Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder. Advances in diffusion magnetic resonance imaging (MRI) acquisition sequences and analytic techniques have led to growing body of evidence that abnormal white matter microstructure is a core pathophysiological feature of ADHD. This systematic review provides a qualitative assessment of research investigating microstructural organisation of white matter amongst children and adolescents with ADHD. This review included 46 studies in total, encompassing multiple diffusion MRI imaging techniques and analytic approaches, including whole-brain, region of interest and connectomic analyses. Whole-brain and region of interest analyses described atypical organisation of white matter microstructure in several white matter tracts: most notably in frontostriatal tracts, corpus callosum, superior longitudinal fasciculus, cingulum bundle, thalamic radiations, internal capsule and corona radiata. Connectomic analyses, including graph theory approaches, demonstrated global underconnectivity in connections between functionally specialised networks. Although some studies reported significant correlations between atypical white matter microstructure and ADHD symptoms or other behavioural measures there was no clear pattern of results. Interestingly however, many of the findings of disrupted white matter microstructure were in neural networks associated with key neuropsychological functions that are atypical in ADHD. Limitations to the extant research are outlined in this review and future studies in this area should carefully consider factors such as sample size, sex balance, head motion and medication status.

Segmental abnormalities of superior longitudinal fasciculus microstructure in patients with schizophrenia, bipolar disorder, and attention-deficit/hyperactivity disorder: An automated fiber quantification tractography study

INTRODUCTION

Superior longitudinal fasciculus (SLF) is a white matter (WM) tract that connects the frontal, parietal and temporal lobes. SLF integrity has been widely assessed in neuroimaging studies of psychiatric disorders, such as schizophrenia (SZ), bipolar disorder (BD), and attention-deficit/hyperactivity disorder (ADHD). However, prior studies have revealed inconsistent findings and comparisons across disorders have not been fully examined.

METHODS

Here, we obtained data for 113 patients (38 patients with SZ, 40 with BD, 35 with ADHD) and 94 healthy controls from the UCLA Consortium for Neuropsychiatric Phenomic LA5c dataset. We assessed the integrity of 20 major WM tracts with a novel segmentation method by automating fiber tract quantification (AFQ). The AFQ divides each tract into 100 equal parts along the direction of travel, with fractional anisotropy (FA) of each part taken as a characteristic. Differences in FA among the four groups were examined.

RESULTS

Compared to healthy controls, patients with SZ showed significantly lower FA in the second half (51-100 parts) of the SLF. No differences were found between BD and healthy controls, nor between ADHD and healthy controls. Results also demonstrated that patients with SZ showed FA reduction in the second half of the SLF relative to patients with BP. Moreover, greater FA in patients in SLF was positively correlated with the manic-hostility score of the Brief Psychiatry Rating scale.

DISCUSSION

These findings indicated that differences in focal changes in SLF might be a key neurobiological abnormality contributing to characterization of these psychiatric disorders.

Regional Topological Aberrances of White Matter- and Gray Matter-Based Functional Networks for Attention Processing May Foster Traumatic Brain Injury-Related Attention Deficits in Adults

Traumatic brain injury (TBI) is highly prevalent in adults. TBI-related functional brain alterations have been linked with common post-TBI neurobehavioral sequelae, with unknown neural substrates. This study examined the systems-level functional brain alterations in white matter (WM) and gray matter (GM) for visual sustained-attention processing, and their interactions and contributions to post-TBI attention deficits. Task-based functional MRI data were collected from 42 adults with TBI and 43 group-matched normal controls (NCs), and analyzed using the graph theoretic technique. Global and nodal topological properties were calculated and compared between the two groups. Correlation analyses were conducted between the neuroimaging measures that showed significant between-group differences and the behavioral symptom measures in attention domain in the groups of TBI and NCs, respectively. Significantly altered nodal efficiencies and/or degrees in several WM and GM nodes were reported in the TBI group, including the posterior corona radiata (PCR), posterior thalamic radiation (PTR), postcentral gyrus (PoG), and superior temporal sulcus (STS). Subjects with TBI also demonstrated abnormal systems-level functional synchronization between the PTR and STS in the right hemisphere, hypo-interaction between the PCR and PoG in the left hemisphere, as well as the involvement of systems-level functional aberrances in the PCR in TBI-related behavioral impairments in the attention domain. The findings of the current study suggest that TBI-related systems-level functional alterations associated with these two major-association WM tracts, and their anatomically connected GM regions may play critical role in TBI-related behavioral deficits in attention domains.

Imaging modalities in differential diagnosis of Parkinson’s disease: opportunities and challenges

Background

Parkinson’s disease (PD) diagnosis is yet largely based on the related clinical aspects. However, genetics, biomarkers, and neuroimaging studies have demonstrated a confirming role in the diagnosis, and future developments might be used in a pre-symptomatic phase of the disease.

Main text

This review provides an update on the current applications of neuroimaging modalities for PD diagnosis. A literature search was performed to find published studies that were involved on the application of different imaging modalities for PD diagnosis. An organized search of PubMed/MEDLINE, Embase, ProQuest, Scopus, Cochrane, and Google Scholar was performed based on MeSH keywords and suitable synonyms. Two researchers (TM and JPI) independently and separately performed the literature search. Our search strategy in each database was done by the following terms: ((Parkinson [Title/Abstract]) AND ((“Parkinsonian syndromes ”[Mesh]) OR Parkinsonism [Title/Abstract])) AND ((PET [Title/Abstract]) OR “SPECT”[Mesh]) OR ((Functional imaging, Transcranial sonography [Title/Abstract]) OR “Magnetic resonance spectroscopy ”[Mesh]). Database search had no limitation in time, and our last update of search was in February 2021. To have a comprehensive search and to find possible relevant articles, a manual search was conducted on the reference list of the articles and limited to those published in English.

Conclusion

Early diagnosis of PD could be vital for early management and adequate neuroprotection. Recent neuroimaging modalities such as SPECT and PET imaging using radiolabeled tracers, MRI, and CT are used to discover the disease. By the modalities, it is possible to early diagnose dopaminergic degeneration and also to differentiate PD from others parkinsonian syndromes, to monitor the natural progression of the disease and the effect of neuroprotective treatments on the progression. In this regard, functional imaging techniques have provided critical insights and roles on PD.

Functional constipation is associated with alterations in thalamo-limbic/parietal structural connectivity

BACKGROUND

Functional constipation (FCon) is a common functional gastrointestinal disorder (FGID) with a high prevalence in clinical practice. Previous studies have identified that FCon is associated with functional and structural alterations in the primary brain regions involved in emotional arousal processing, sensory processing, somatic/motor-control, and self-referential processing. However, whether FCon is associated with abnormal structural connectivity (SC) among these brain regions remains unclear.

METHODS

We selected the brain regions with functional and structural abnormalities as seed regions and employed diffusion tensor imaging (DTI) with probabilistic tractography to investigate SC changes in 29 patients with FCon and 31 healthy controls (HC).

KEY RESULTS

Results showed lower fractional anisotropy (FA) in the fibers connecting the thalamus, a region involved in sensory processing, with the amygdala (AMY), hippocampal gyrus (HIPP), precentral (PreCen) and postcentral gyrus (PostCen), supplementary motor area (SMA) and precuneus in patients with FCon compared with HC. FCon had higher mean diffusivity (MD) and radial diffusivity (RD) in the thalamus connected to the AMY and HIPP. In addition, FCon had significantly increased RD of the thalamus-SMA tract. Sensation of incomplete evacuation was negatively correlated with FA of the thalamus-PostCen and thalamus-HIPP tracts, and there was a negative correlation between difficulty of defecation and FA of the thalamus-SMA tract.

CONCLUSIONS AND INFERENCES

These findings reflected that FCon is associated with alterations in SC between the thalamus and limbic/parietal cortex, highlighting the integrative role of the thalamus in brain structural network.

rsHRF: A toolbox for resting-state HRF estimation and deconvolution

The hemodynamic response function (HRF) greatly influences the intra- and inter-subject variability of brain activation and connectivity, and might confound the estimation of temporal precedence in connectivity analyses, making its estimation necessary for a correct interpretation of neuroimaging studies. Additionally, the HRF shape itself is a useful local measure. However, most algorithms for HRF estimation are specific for task-related fMRI data, and only a few can be directly applied to resting-state protocols. Here we introduce rsHRF, a Matlab and Python toolbox that implements HRF estimation and deconvolution from the resting-state BOLD signal. We first provide an overview of the main algorithm, practical implementations, and then demonstrate the feasibility and usefulness of rsHRF by validation experiments with a publicly available resting-state fMRI dataset. We also provide tools for statistical analyses and visualization. We believe that this toolbox may significantly contribute to a better analysis and understanding of the components and variability of BOLD signals.

Neurosteroid-based intervention using Ganaxolone and Emapunil for improving stress-induced myelination deficits and neurobehavioural disorders

BACKGROUND

Prenatal stress is associated with long-term disturbances in white matter development and behaviour in children, such as attention deficit hyperactivity disorder (ADHD) and anxiety. Oligodendrocyte maturation and myelin formation is a tightly orchestrated process beginning during gestation, and therefore is very vulnerable to the effects of maternal prenatal stresses in mid-late pregnancy. The current study aimed to examine the effects of prenatal stress on components of the oligodendrocyte lineage to identify the key processes that are disrupted and to determine if postnatal therapies directed at ameliorating white matter deficits also improve behavioural outcomes.

METHODS

Pregnant guinea pig dams were exposed to control-handling or prenatal stress with strobe light exposure for 2hrs/day on gestational age (GA) 50, 55, 60 and 65, and allowed to spontaneously deliver ~GA70. Pups were administered oral ganaxolone (5 mg/kg/day in 45% cyclodextrin) or the TSPO agonist, emapunil (XBD173; 0.3 mg/kg/day in 1% tragacanth gum) or vehicle, on postnatal days (PND) 1-7. Behavioural outcomes were assessed using open field and elevated plus maze testing on PND7 and PND27. Hippocampal samples were collected at PND30 to assess markers of oligodendrocyte development through assessment of total oligodendrocytes (OLIG2) and mature cells (myelin basic protein; MBP), and total neurons (NeuN) by immunostaining. Real-time PCR was conducted on hippocampal regions to assess markers of the oligodendrocyte lineage, markers of neurogenesis and components of the neurosteroidogenesis pathway. Plasma samples were collected for steroid quantification of cortisol, allopregnanolone, progesterone and testosterone by ELISA.

RESULTS

Prenatal stress resulted in hyperactivity in male offspring, and anxiety-like behaviour in female offspring in the guinea pig at an age equivalent to late childhood. Postnatal ganaxolone and emapunil treatment after prenatal stress restored the behavioural phenotype to that of control in females only. The oligodendrocyte maturation lineage, translation of MBP mRNA-to-protein, and neurogenesis were disrupted in prenatally-stressed offspring, resulting in a decreased amount of mature myelin. Emapunil treatment restored mature myelin levels in both sexes, and reversed disruptions to the oligodendrocyte lineage in female offspring, an effect not seen with ganaxolone treatment.

CONCLUSION

The marked and persisting behavioural and white matter perturbations observed in a clinically relevant guinea pig model of prenatal stress highlights the need for postnatal interventions that increase myelin repair and improve long-term outcomes. The effectiveness of emapunil treatment in restoring female offspring behaviour, and promoting maturation of myelin indicates that early therapeutic interventions can reverse the damaging effects of major stressful events in pregnancy. Further studies optimising target mechanisms and dosing are warranted.

Sex-specific patterns of white matter microstructure are associated with emerging depression during adolescence

Prior research has demonstrated associations between adolescent depression and alterations in the white matter microstructure of fiber tracts implicated in emotion regulation. Using diffusion tensor imaging, this study explored premorbid, sex-specific white matter microstructural features that related to future emergence of major depressive disorder (MDD) during adolescence and young adulthood. Adolescents from the National Consortium on Alcohol and Neurodevelopment in Adolescence study, who were 12-21 years old at study entry and had not experienced major depression as of the baseline assessment, were selected for inclusion (N = 462, n = 223 female adolescents). Over five years of annual follow-up, 63 participants developed a diagnosis of MDD, as determined by the Computerized Semi-Structured Assessment for the Genetics of Alcoholism (n = 39 female adolescents). A whole-brain multivariate modeling approach was used to examine the relationship between fractional anisotropy (FA) at baseline and emergence into MDD, as a function of sex, controlling for age at baseline. Among female adolescents, those who developed MDD had significantly lower baseline FA in a portion of left precentral gyrus white matter, while male adolescents exhibited the opposite pattern. These results may serve as indirect microstructural markers of risk and targets for the prevention of depression during adolescence.

Is Structural Connectivity Different in Child and Adolescent Relatives of Patients with Bipolar Disorder? A Narrative Review According to Studies with DTI

INTRODUCTION

Bipolar disorder (BD) has been associated with a decrease in white matter integrity. Diffusion tensor imaging (DTI) studies have enabled these changes to be elucidated with higher quality. Due to BD's high heritability, some studies have been conducted in relatives of BD patients looking at white matter integrity, and have found that structural connectivity may also be affected. This alteration has been proposed as a potential BD biomarker of vulnerability. However, there are few studies in children and adolescents.

OBJECTIVE

To conduct a review of the literature on changes in white matter integrity determined by DTI in high-risk children and adolescents.

RESULTS

Brain structural connectivity in the paediatric population is described in studies using DTI. Changes in the myelination process from its evolution within normal neurodevelopment to the findings in fractional anisotropy (FA) in BD patients and their high-risk relatives are also described.

CONCLUSIONS

Studies show that both BD patients and their at-risk relatives present a decrease in FA in specific brain regions. Studies in children and adolescents with a high risk of BD, indicate a reduced FA in axonal tracts involved in emotional and cognitive functions. Decreased FA can be considered as a vulnerability biomarker for BD.

Integrity of the uncinate fasciculus is associated with the onset of bipolar disorder: a 6-year followed-up study

Patients with Bipolar Disorder (BD) are associated with aberrant uncinate fasciculus (UF) that connects amygdala-ventral prefrontal cortex (vPFC) system, but the casual relationship is still uncertain. The research aimed to investigate the integrity of UF among offspring of patients with BD and investigate its potential causal association with subsequent declaration of BD. The fractional anisotropy (FA) and mean diffusivity (MD) of UF were compared in asymptomatic offspring (AO, n = 46) and symptomatic offspring (SO, n = 45) with a parent with BD, and age-matched healthy controls (HCs, n = 35). Logistic regressions were performed to assess the predictive effect of UF integrity on the onset of BD. The three groups did not differ at baseline in terms of FA and MD of the UF. Nine out of 45 SO developed BD over a follow-up period of 6 years, and the right UF FA predicted the onset of BD (p = 0.038, OR = 0.212, 95% CI = 0.049-0.917). The ROC curve revealed that the right UF FA predicted BD onset (area-under-curve = 0.859) with sensitivity of 88.9% and specificity of 77.3%. The complementary whole-brain tract-based spatial statistics (TBSS) showed that widespread increases of FA were found in the SO group compared with HCs, but were not associated with the onset of BD. Our data provide evidence supporting the causal relationship between the white matter structural integrity of the amygdala-vPFC system and the onset of BD in genetically at-risk offspring of BD patients.

White matter correlates of cognitive flexibility in youth with bipolar disorder and typically developing children and adolescents

Prior studies using behavioral tasks and neuroimaging have shown that children and adolescents with bipolar disorder (BD) have deficits in cognitive flexibility (CF)-defined as adaptation to changing rewards and punishments. However, no study, to our knowledge, has examined the white matter microstructural correlates of CF in youth with BD. To address this gap, we examined the relationship between CF assessed with the Cambridge Neuropsychological Testing Automated Battery (CANTAB)'s Intra-Extra Dimensional Set Shift task (ID/ED) and diffusion tensor imaging analyzed with FSL's preprocessing tools and Tract-Based Spatial Statistics (TBSS). We found a significantly different relationship between microstructural integrity of multiple white matter regions and CF performance in BD (n=28) and age-matched typically developing control (TDC) youths (n=26). Evaluation of the slopes of linear regressions in BD vs. TDC (ID/ED Simple Reversal error rate vs. fractional anisotropy) revealed significantly different slopes across the groups, indicating an aberrant relationship between CF and underlying white matter microstructure in youth with BD. These results underscore the importance of examining specific CF-neuroimaging relationships in BD youth. Future longitudinal studies could seek to define the white matter microstructural trajectories in BD vs. TDC, and relative to CF deficits and BD illness course.

Predictors of Concussion Outcomes in Individuals With ADHD

OBJECTIVES

To describe and delineate the epidemiological profile of concussion injuries in individuals with attention-deficit/hyperactivity disorder (ADHD) by identifying characteristics associated with poorer outcomes.

SETTING

One hundred forty-four multidisciplinary concussion-specialized clinics across Canada.

PARTICIPANTS

Two hundred twenty-two individuals with a diagnosis of ADHD aged 7 to 53 years who sustained a concussion within the last year.

DESIGN

Multicenter cohort study.

MAIN MEASURES

Candidate predictor variables (ie, age, sex, concussion history, loss of consciousness, and internalized and learning disorder comorbidities) were collected through oral interviews. Concussion outcomes (ie, symptom severity and total number of symptoms experienced) were assessed with the Sport Concussion Assessment Tool.

RESULTS

Older age, female sex, and the presence of an internalized disorder predicted poorer concussion outcomes in individuals with ADHD. Males with ADHD reported significantly worse concussion outcomes with increasing age, while outcomes remained fairly stable across age in females.

CONCLUSION

The current findings represent a promising step toward the optimization of concussion management in individuals with ADHD. With a more thorough understanding of the demographic and comorbidity variables, clinical care decisions and intervention strategies can be developed to help individuals with ADHD who might be at a higher risk of poorer outcomes following a concussion.

Multimodal dopamine transporter (DAT) imaging and magnetic resonance imaging (MRI) to characterise early Parkinson's disease

Idiopathic Parkinson's disease (PD), the second most common neurodegenerative disorder, is characterised by the progressive loss of dopaminergic nigrostriatal terminals. Currently, in early idiopathic PD, dopamine transporter (DAT)-specific imaging assesses the extent of striatal dopaminergic deficits, and conventional magnetic resonance imaging (MRI) of the brain excludes the presence of significant ischaemic load in the basal ganglia as well as signs indicative of other forms of Parkinsonism. In this article, we discuss the use of multimodal DAT-specific and MRI protocols for insight into the early pathological features of idiopathic PD, including: structural MRI, diffusion tensor imaging, nigrosomal iron imaging and neuromelanin-sensitive MRI sequences. These measures may be acquired serially or simultaneously in a hybrid scanner. From current evidence, it appears that both nigrosomal iron imaging and neuromelanin-sensitive MRI combined with DAT-specific imaging are useful to assist clinicians in diagnosing PD, while conventional structural MRI and diffusion tensor imaging protocols are better suited to a research context focused on characterising early PD pathology. We believe that in the future multimodal imaging will be able to characterise prodromal PD and stratify the clinical stages of PD progression.

Neuropsychology of Bipolar Disorder

Bipolar disorder is associated with significant dysfunction in a broad range of neuropsychological domains and processes. Deficits have been reported to occur in symptomatic states (depression, [hypo]mania) as well as in remission (euthymia), having consequences for psychological well-being and social and occupational functioning. The profile and magnitude of neuropsychological deficits in bipolar disorder have been explored in a number of systematic reviews and meta-analyses. After discussing these briefly, this chapter will focus on examining the clinical and demographic factors that influence and modify the pattern and magnitude of deficits, as well as reviewing methods of assessment and analysis approaches which may improve our understanding of these problems.

Myelination- and immune-mediated MR-based brain network correlates

Background

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS), characterized by inflammatory and neurodegenerative processes. Despite demyelination being a hallmark of the disease, how it relates to neurodegeneration has still not been completely unraveled, and research is still ongoing into how these processes can be tracked non-invasively. Magnetic resonance imaging (MRI) derived brain network characteristics, which closely mirror disease processes and relate to functional impairment, recently became important variables for characterizing immune-mediated neurodegeneration; however, their histopathological basis remains unclear.

Methods

In order to determine the MRI-derived correlates of myelin dynamics and to test if brain network characteristics derived from diffusion tensor imaging reflect microstructural tissue reorganization, we took advantage of the cuprizone model of general demyelination in mice and performed longitudinal histological and imaging analyses with behavioral tests. By introducing cuprizone into the diet, we induced targeted and consistent demyelination of oligodendrocytes, over a period of 5 weeks. Subsequent myelin synthesis was enabled by reintroduction of normal food.

Results

Using specific immune-histological markers, we demonstrated that 2 weeks of cuprizone diet induced a 52% reduction of myelin content in the corpus callosum (CC) and a 35% reduction in the neocortex. An extended cuprizone diet increased myelin loss in the CC, while remyelination commenced in the neocortex. These histologically determined dynamics were reflected by MRI measurements from diffusion tensor imaging. Demyelination was associated with decreased fractional anisotropy (FA) values and increased modularity and clustering at the network level. MRI-derived modularization of the brain network and FA reduction in key anatomical regions, including the hippocampus, thalamus, and analyzed cortical areas, were closely related to impaired memory function and anxiety-like behavior.

Conclusion

Network-specific remyelination, shown by histology and MRI metrics, determined amelioration of functional performance and neuropsychiatric symptoms. Taken together, we illustrate the histological basis for the MRI-driven network responses to demyelination, where increased modularity leads to evolving damage and abnormal behavior in MS. Quantitative information about in vivo myelination processes is mirrored by diffusion-based imaging of microstructural integrity and network characteristics.

The anterior limb of the internal capsule: Anatomy, function, and dysfunction

The last two decades have seen a re-emergence of neurosurgery for severe, refractory psychiatric diseases, largely due to the advent of more precise and safe operative techniques. Nevertheless, the optimal targets for these surgeries remain a matter of debate, and are often grandfathered from experiences in the late 20th century. To better explore the rationale for one target in particular - the anterior limb of the internal capsule (ALIC) - we comprehensively reviewed all available literature on its role in the pathophysiology and treatment of mental illness. We first provide an overview of its functional anatomy, followed by a discussion on its role in several prevalent psychiatric diseases. Given its structural integration into the limbic system and involvement in a number of cognitive and emotional processes, the ALIC is a robust target for surgical treatment of refractory psychiatric diseases. The advent of novel neuroimaging techniques, coupled with image-guided therapeutics and neuromodulatory treatments, will continue to enable study on the ALIC in mental illness.

Quantitative tractography reveals changes in the corticospinal tract in drug-naïve children with attention-deficit/hyperactivity disorder

BACKGROUND

The specific role of the corticospinal tract with respect to inattention and impulsive symptoms in children with attention-deficit/hyperactivity disorder (ADHD) has been explored in the past. However, to our knowledge, no study has identified the exact regions of the corticospinal tract that are affected in ADHD. We aimed to determine comprehensive alterations in the white matter microstructure of the corticospinal tract and underlying neuropsychological substrates in ADHD.

METHODS

We recruited 38 drug-naïve children with ADHD and 34 typically developing controls. We employed a tract-based quantitative approach to measure diffusion parameters along the trajectory of the corticospinal tract, and we further correlated alterations with attention and response inhibition measures.

RESULTS

Compared with controls, children with ADHD demonstrated significantly lower fractional anisotropy and higher radial diffusivity at the level of cerebral peduncle, and higher fractional anisotropy at the level of the posterior limb of the internal capsule in the right corticospinal tract only. As well, increased fractional anisotropy in the posterior limb of the internal capsule was negatively correlated with continuous performance test attention quotients and positively correlated with reaction time on the Stroop Colour–Word Test; increased radial diffusivity in the right peduncle region was positively correlated with omissions in the Stroop test.

LIMITATIONS

The sample size was relatively small. Moreover, we did not consider the different subtypes of ADHD and lacked sufficient power to analyze subgroup differences. Higher-order diffusion modelling is needed in future white matter studies.

CONCLUSION

We demonstrated specific changes in the right corticospinal tract in children with ADHD. Correlations with measures of attention and response inhibition underscored the functional importance of corticospinal tract disturbance in ADHD.

Alterations in the fronto-limbic network and corpus callosum in borderline-personality disorder

Neuroimaging research provides evidence of grey matter changes in the prefrontal-limbic network in borderline personality disorder (BPD), yet research scarcely examines the white matter (WM) within this circuitry. The present study aimed to explore WM in prefrontal-limbic brain networks within BPD. Quantitative diffusion tensor imaging (DTI-MRI) measures of fractional anisotropy (FA) and mean diffusion (MD) were used to analyze the neural pathways in fifteen individuals with BPD (M = 25, SD = 6.76), in comparison to thirteen healthy individuals (M = 27.92, SD = 8.41). Quantitative DTI-MRI measures of FA and MD were evaluated for the cingulum, the fornix, the corpus callosum (CC), the inferior longitudinal fasciculus (ILF), the superior longitudinal fasciculus (SLF) and the uncinate fasciculus (UF). Lower FA values for both the left and the right cingulum, the genu, body, and splenium of the CC, left ILF and right SLF were found in BPD, compared to healthy individuals. MD values were higher for the genu and splenium of the CC in BPD. The findings indicate that a large-scale emotional brain network is affected in BPD with alterations in MD and FA of WM prefrontal-limbic pathways of the heteromodal association cortex involved in emotion processing and emotion regulation.

Maturation of Brain Microstructure and Metabolism Associates with Increased Capacity for Self-Regulation during the Transition from Childhood to Adolescence

Children ages 9-12 years face increasing social and academic expectations that require mastery of their thoughts, emotions, and behavior. Little is known about the development of neural pathways integral to these improving capacities during the transition from childhood to adolescence. Among 234 healthy, inner-city male and female youth (species Homo sapiens) 9-12 years of age followed by the Columbia Center for Children's Environmental Health, we acquired diffusion tensor imaging, multiplanar chemical shift imaging, and cognitive measures requiring self-regulation. We found that increasing age was associated with increased fractional anisotropy and decreased apparent diffusion coefficient, most prominently in the frontal and cingulate cortices, striatum, thalamus, deep white matter, and cerebellum. Additionally, we found increasing age was associated with increased N-acetyl-l-aspartate (NAA) in the anterior cingulate and insular cortices, and decreased NAA in posterior cingulate and parietal cortices. Age-associated changes in microstructure and neurometabolite concentrations partially mediated age-related improvements in performance on executive function tests. Together, these findings suggest that maturation of key regions within cortico-striatal-thalamo-cortical circuits subserve the emergence of improved self-regulatory capacities during the transition from childhood to adolescence.SIGNIFICANCE STATEMENT Few imaging studies of normal brain development have focused on a population of inner-city, racial/ethnic minority youth during the transition from childhood to adolescence, a period when self-regulatory capacities rapidly improve. We used DTI and MPCSI to provide unique windows into brain maturation during this developmental epoch, assessing its mediating influences on age-related improvement in performance on self-regulatory tasks. Our findings suggest that rapid maturation of cortico-striato-thalamo-cortical circuits, represented as progressive white-matter maturation (increasing FA and increasing NAA, Ch, Cr concentrations accompanying advancing age) in frontal regions and related subcortical projections and synaptic pruning (decreasing NAA, Ch, Cr, Glx) in posterior regions, support age-related improvements in executive functioning and self-regulatory capacities in youth 9-12 years of age.

Differential neuroimaging indices in prefrontal white matter in prenatal alcohol-associated ADHD versus idiopathic ADHD

BACKGROUND

Attention deficit-hyperactivity disorder (ADHD) is common in fetal alcohol spectrum disorders (FASD) but also in patients without prenatal alcohol exposure (PAE). Many patients diagnosed with idiopathic ADHD may actually have ADHD and covert PAE, a treatment-relevant distinction.

METHODS

We compared proton magnetic resonance spectroscopic imaging (MRSI; N = 44) and diffusion tensor imaging (DTI; N = 46) of the anterior corona radiata (ACR)-a key fiber tract in models of ADHD-at 1.5 T in children with ADHD with PAE (ADHD+PAE), children with ADHD without PAE (ADHD-PAE), children without ADHD with PAE (non-ADHD+PAE), and children with neither ADHD nor PAE (non-ADHD-PAE, i.e., typically developing controls). Levels of choline-compounds (Cho) were the main MRSI endpoint, given interest in dietary choline for FASD; the main DTI endpoint was fractional anisotropy (FA), as ACR FA may reflect ADHD-relevant executive control functions.

RESULTS

For ACR Cho, there was an ADHD-by-PAE interaction (p = 0.038) whereby ACR Cho was 26.7% lower in ADHD+PAE than in ADHD-PAE children (p < 0.0005), but there was no significant ACR Cho difference between non-ADHD+PAE and non-ADHD-PAE children. Voxelwise false-discovery rate (FDR)-corrected analysis of DTI revealed significantly (q ≤ 0.0101-0.05) lower FA in ACR for subjects with PAE (ADHD+PAE or non-ADHD+PAE) than for subjects without PAE (ADHD-PAE or non-ADHD-PAE). There was no significant effect of ADHD on FA. Thus, in overlapping samples, effects of PAE on Cho and FA were observed in the same white-matter tract.

CONCLUSIONS

These findings point to tract focal, white-matter pathology possibly specific for ADHD+PAE subjects. Low Cho may derive from abnormal choline metabolism; low FA suggests suboptimal white-matter integrity in PAE. More advanced MRSI and DTI-and neurocognitive assessments-may better distinguish ADHD+PAE from ADHD-PAE, helping identify covert cases of FASD.

Effects of illness duration on cognitive performances in bipolar depression are mediated by white matter microstructure

BACKGROUND

Cognitive deficits are a core feature of bipolar disorder (BD), and persist during the euthymic phase. White matter (WM) microstructural abnormalities are widely considered a structural marker of BD. Features of illness chronicity, such as illness duration and number of mood episodes, have been associated with worsening of both clinical profile and brain structural alterations. This study examined the role of WM integrity as a possible mediator between illness duration and cognitive performances in a sample of BD patients.

METHODS

We assessed 88 inpatients affected by a depressive episode in course of type I BD for verbal memory, visual memory, working memory, visuospatial constructional abilities, psychomotor coordination, executive functions, processing speed, and verbal fluency. White matter integrity was evaluated through FA measurements derived using the Enhancing Neuro Imaging Genetics Through Meta-Analysis (ENIGMA)-DTI protocol.

RESULTS

The effect of illness duration on processing speed, verbal memory, and visual memory was mediated by the FA values of bilateral anterior corona radiata, bilateral corona radiata, genu of corpus callosum, and fornix, adjusting for age, sex, education and lithium treatment (p < 0.05).

LIMITATIONS

Potential interaction factors were not examined in this study.

CONCLUSIONS

This is the first study to show the role of WM integrity as a mediator of the negative effect of illness duration on cognitive performances. Our data provide new insight into the neuroprogressive hypothesis of BD.

Stressful Life Events, ADHD Symptoms, and Brain Structure in Early Adolescence

Despite a growing understanding that early adversity in childhood broadly affects risk for psychopathology, the contribution of stressful life events to the development of symptoms of attention-deficit/hyperactivity disorder (ADHD) is not clear. In the present study, we examined the association between number of stressful life events experienced and ADHD symptoms, assessed using the Attention Problems subscale of the Child Behavior Checklist, in a sample of 214 children (43% male) ages 9.11-13.98 years (M = 11.38, SD = 1.05). In addition, we examined whether the timing of the events (i.e., onset through age 5 years or after age 6 years) was associated with ADHD symptoms. Finally, we examined variation in brain structure to determine whether stressful life events were associated with volume in brain regions that were found to vary as a function of symptoms of ADHD. We found a small to moderate association between number of stressful life events and ADHD symptoms. Although the strength of the associations between number of events and ADHD symptoms did not differ as a function of the age of occurrence of stressful experiences, different brain regions were implicated in the association between stressors and ADHD symptoms in the two age periods during which stressful life events occurred. These findings support the hypothesis that early adversity is associated with ADHD symptoms, and provide insight into possible brain-based mediators of this association.

White Matter Microstructure Associations of Cognitive and Visuomotor Control in Children: A Sensory Processing Perspective

Objective: Recent evidence suggests that co-occurring deficits in cognitive control and visuomotor control are common to many neurodevelopmental disorders. Specifically, children with sensory processing dysfunction (SPD), a condition characterized by sensory hyper/hypo-sensitivity, show varying degrees of overlapping attention and visuomotor challenges. In this study, we assess associations between cognitive and visuomotor control abilities among children with and without SPD. In this same context, we also examined the common and unique diffusion tensor imaging (DTI) tracts that may support the overlap of cognitive control and visuomotor control. Method: We collected cognitive control and visuomotor control behavioral measures as well as DTI data in 37 children with SPD and 25 typically developing controls (TDCs). We constructed regressions to assess for associations between behavioral performance and mean fractional anisotropy (FA) in selected regions of interest (ROIs). Results: We observed an association between behavioral performance on cognitive control and visuomotor control. Further, our findings indicated that FA in the anterior limb of the internal capsule (ALIC), the anterior thalamic radiation (ATR), and the superior longitudinal fasciculus (SLF) are associated with both cognitive control and visuomotor control, while FA in the superior corona radiata (SCR) uniquely correlate with cognitive control performance and FA in the posterior limb of the internal capsule (PLIC) and the cerebral peduncle (CP) tract uniquely correlate with visuomotor control performance. Conclusions: These findings suggest that children who demonstrate lower cognitive control are also more likely to demonstrate lower visuomotor control, and vice-versa, regardless of clinical cohort assignment. The overlapping neural tracts, which correlate with both cognitive and visuomotor control suggest a possible common neural mechanism supporting both control-based processes.

Patients with chronic bipolar disorder exhibit widespread increases in extracellular free water

OBJECTIVES

Bipolar disorder (BP) is a debilitating psychiatric disease that is not well understood. Previous diffusion magnetic resonance imaging (dMRI) studies of BP patients found prominent microstructural white matter (WM) abnormalities of reduced fractional anisotropy (FA). Because FA is a nonspecific measure, relating these abnormalities to a specific pathology is difficult. Here, dMRI specificity was increased by free water (FW) imaging, which allows identification of changes in extracellular space (FW) from neuronal tissue (fractional anisotropy of tissue [FA-t]). Previous studies identified increased FW in early schizophrenia (SZ) stages which was replaced by widespread decreased FA-t in chronic stages. This is the first analysis utilizing this method to compare BP patients and controls.

METHODS

3 Tesla diffusion weighted imaging (3T DWI) data were acquired for 17 chronic BP and 28 healthy control (HC) participants at Oxford University. Tract-based spatial statistics was utilized to generate a WM skeleton. FW imaging deconstructed the diffusion signal into extracellular FW and tissue FA-t maps. These maps were projected onto the skeleton and FA, FA-t, and FW were compared between groups.

RESULTS

We found significantly lower FA in BP patients when compared to HC in areas that overlapped with extensive FW increases. There were no FA-t differences.

CONCLUSIONS

Our study suggests that chronic BP shows similar WM changes to early SZ, suggesting that extracellular FW increases could be a transient indication of recent psychotic episodes. Since FW increase in SZ has been suggested to be related to neuroinflammation, we theorize that neuroinflammation might be a shared pathology between chronic BP and early SZ.

The cingulum bundle: Anatomy, function, and dysfunction

The cingulum bundle is a prominent white matter tract that interconnects frontal, parietal, and medial temporal sites, while also linking subcortical nuclei to the cingulate gyrus. Despite its apparent continuity, the cingulum's composition continually changes as fibres join and leave the bundle. To help understand its complex structure, this review begins with detailed, comparative descriptions of the multiple connections comprising the cingulum bundle. Next, the impact of cingulum bundle damage in rats, monkeys, and humans is analysed. Despite causing extensive anatomical disconnections, cingulum bundle lesions typically produce only mild deficits, highlighting the importance of parallel pathways and the distributed nature of its various functions. Meanwhile, non-invasive imaging implicates the cingulum bundle in executive control, emotion, pain (dorsal cingulum), and episodic memory (parahippocampal cingulum), while clinical studies reveal cingulum abnormalities in numerous conditions, including schizophrenia, depression, post-traumatic stress disorder, obsessive compulsive disorder, autism spectrum disorder, Mild Cognitive Impairment, and Alzheimer's disease. Understanding the seemingly diverse contributions of the cingulum will require better ways of isolating pathways within this highly complex tract.

Preliminary mapping of the structural effects of age in pediatric bipolar disorder with multimodal MR imaging

This study investigates multimodal structural MR imaging biomarkers of development trajectories in pediatric bipolar disorder. T1-weighted and diffusion-weighted MR imaging was conducted to investigate cross-sectional group differences with age between typically developing controls (N = 26) and youths diagnosed with bipolar disorder (N = 26). Region-based analysis was used to examine cortical thickness of gray matter and diffusion tensor parameters in superficial white matter, and tractography-based analysis was used to examine deep white matter fiber bundles. Patients and controls showed significantly different maturation trajectories across brain areas; however, the magnitude of differences varied by region. The rate of cortical thinning with age was greater in patients than controls in the left frontal pole. While controls showed increasing fractional anisotropy (FA) and axial diffusivity (AD) with age, patients showed an opposite trend of decreasing FA and AD with age in fronto-temporal-striatal regions located in both superficial and deep white matter. The findings support fronto-temporal-striatal alterations in the developmental trajectories of youths diagnosed with bipolar disorder, and further, show the value of multimodal computational techniques in the assessment of neuropsychiatric disorders. These preliminary results warrant further investigation into longitudinal changes and the effects of treatment in the brain areas identified in this study.

Longitudinal Diffusion Tensor Imaging Study of Adolescents and Young Adults With Bipolar Disorder

OBJECTIVE

Longitudinal neuroimaging during adolescence/young adulthood, when bipolar disorder (BD) commonly emerges, can help elucidate the neurodevelopmental pathophysiology of BD. Adults with BD have shown reduced structural integrity in the uncinate fasciculus (UF), a white matter (WM) tract providing major connections between the amygdala and ventral prefrontal cortex (vPFC), important in emotion regulation. In this longitudinal diffusion tensor imaging (DTI) study of adolescents/young adults, we hypothesized differences in age- and time-related changes in UF integrity in BD compared to healthy controls (HC).

METHOD

Two DTI scans were obtained in 27 adolescents/young adults with BD and 37 HC adolescents/young adults, on average approximately 2.5 years apart. Interactions between diagnosis with age and with time for UF fractional anisotropy (FA) were assessed. Exploratory analyses were performed including euthymic-only participants with BD, and for potential influences of demographic and clinical factors. Whole-brain analyses were performed to explore for interactions in other regions.

RESULTS

There were significant interactions between diagnosis with age and with time for UF FA (p < .05). Healthy control adolescents/young adults showed significant UF FA increases with age and over time (p < .05), whereas no significant changes with age or over time were observed in the adolescents/young adults with BD. Significant interactions with age and time were also observed in analyses including euthymic-only participants with BD (p < .05).

CONCLUSION

These findings provide neuroimaging evidence supporting differences in UF WM structural development during adolescence/young adulthood, suggesting that differences in the development of an amygdala-vPFC system subserving emotion regulation may be a trait feature of BD neurodevelopment.

Diffusion imaging study of the Corpus Callosum in bipolar disorder

Structural and diffusion imaging studies have provided some evidence of abnormal organization of Corpus Callosum (CC) in Bipolar Disorder (BD). Therefore, by using Diffusion Weighted Imaging (DWI), which allows to build subtle prediction models of fiber integrity for white matter (WM) tracts, this study aims to further explore the microstructure integrity of CC in BD patients compared to matched healthy controls. Twenty-four chronic patients with BD and 35 healthy controls were included in the study. Circular regions of interest were placed, on diffusion images, in the left and right side of callosal regions (i.e. rostrum/genu, anterior body, posterior body, splenium) and the Apparent Diffusion Coefficient (ADC) was then calculated. Significantly increased ADC values were found in right anterior body and in right splenium in BD patients compared to healthy controls (all p < 0.05, Bonferroni corrected). In this study, we found abnormally increased ADC callosal values in BD suggesting microstructural anomalies specifically in the right hemisphere. Interestingly, this finding further supports the presence of an altered inter-hemispheric communication between frontal and temporo-parietal association areas in patients with BD, which may ultimately result in clinical symptoms and cognitive deficits.

Suprathreshold fiber cluster statistics: Leveraging white matter geometry to enhance tractography statistical analysis

This work presents a suprathreshold fiber cluster (STFC) method that leverages the whole brain fiber geometry to enhance statistical group difference analyses. The proposed method consists of 1) a well-established study-specific data-driven tractography parcellation to obtain white matter tract parcels and 2) a newly proposed nonparametric, permutation-test-based STFC method to identify significant differences between study populations. The basic idea of our method is that a white matter parcel's neighborhood (nearby parcels with similar white matter anatomy) can support the parcel's statistical significance when correcting for multiple comparisons. We propose an adaptive parcel neighborhood strategy to allow suprathreshold fiber cluster formation that is robust to anatomically varying inter-parcel distances. The method is demonstrated by application to a multi-shell diffusion MRI dataset from 59 individuals, including 30 attention deficit hyperactivity disorder patients and 29 healthy controls. Evaluations are conducted using both synthetic and in-vivo data. The results indicate that the STFC method gives greater sensitivity in finding group differences in white matter tract parcels compared to several traditional multiple comparison correction methods.

White matter integrity alterations in post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is a debilitating condition which can develop after exposure to traumatic stressors. Seventy-five adults were recruited from the community, 25 diagnosed with PTSD along with 25 healthy and 25 trauma-exposed age- and gender-matched controls. Participants underwent clinical assessment and magnetic resonance imaging. A previous voxel based morphometry (VBM) study using the same subject cohort identified decreased grey matter (GM) volumes within frontal/subcortical brain regions including the hippocampus, amygdala, and anterior cingulate cortex (ACC). This study examines the microstructural integrity of white matter (WM) tracts connecting the aforementioned regions/structures. Using diffusion tensor imaging, we investigated the integrity of frontal/subcortical WM tracts between all three subject groups. Trauma exposed subjects with and without PTSD diagnosis were identified to have significant disruption in WM integrity as indexed by decreased fractional anisotropy (FA) in the uncinate fasciculus (UF), cingulum cingulate gyrus (CCG), and corpus callosum (CC), when compared with healthy non-trauma-exposed controls. Significant negative correlations were found between total Clinician Administered PTSD scale (CAPS) lifetime clinical subscores and FA values of PTSD subjects in the right UF, CCG, CC body, and right superior longitudinal fasciculus (SLF). An analysis between UF and SLF FA values and VBM determined rostral ACC GM values found a negative correlation in PTSD subjects. Findings suggest that compromised WM integrity in important tracts connecting limbic structures such as the amygdala to frontal regions including the ACC (i.e., the UF and CCG) may contribute to impairments in threat/fear processing associated with PTSD.

The International Society for Bipolar Disorders Task Force report on pediatric bipolar disorder: Knowledge to date and directions for future research

OBJECTIVES

Over the past two decades, there has been tremendous growth in research regarding bipolar disorder (BD) among children and adolescents (ie, pediatric BD [PBD]). The primary purpose of this article is to distill the extant literature, dispel myths or exaggerated assertions in the field, and disseminate clinically relevant findings.

METHODS

An international group of experts completed a selective review of the literature, emphasizing areas of consensus, identifying limitations and gaps in the literature, and highlighting future directions to mitigate these gaps.

RESULTS

Substantial, and increasingly international, research has accumulated regarding the phenomenology, differential diagnosis, course, treatment, and neurobiology of PBD. Prior division around the role of irritability and of screening tools in diagnosis has largely abated. Gold-standard pharmacologic trials inform treatment of manic/mixed episodes, whereas fewer data address bipolar depression and maintenance/continuation treatment. Adjunctive psychosocial treatment provides a forum for psychoeducation and targets primarily depressive symptoms. Numerous neurocognitive and neuroimaging studies, and increasing peripheral biomarker studies, largely converge with prior findings from adults with BD.

CONCLUSIONS

As data have accumulated and controversy has dissipated, the field has moved past existential questions about PBD toward defining and pursuing pressing clinical and scientific priorities that remain. The overall body of evidence supports the position that perceptions about marked international (US vs elsewhere) and developmental (pediatric vs adult) differences have been overstated, although additional research on these topics is warranted. Traction toward improved outcomes will be supported by continued emphasis on pathophysiology and novel therapeutics.

Structural and Functional Abnormalities in Children with Attention-Deficit/Hyperactivity Disorder: A Focus on Subgenual Anterior Cingulate Cortex

Attention-deficit/hyperactivity disorder (ADHD), characterized by developmentally inappropriate inattention, hyperactivity/impulsivity, or a combination of both, is a major public health problem. Neuroimaging studies have revealed associations of these cognitive impairments with structural and functional deficits all over the brain. Existing findings are not fully consistent because of the heterogeneity of study samples and diversity of research techniques. In this study, we propose to utilize a multimodal magnetic resonance imaging (MRI) approach to study the structural and functional brain networks in children with ADHD-combined type (ADHD-C) with a focus on the subgenual anterior cingulate cortex (sgACC). Diffusion tensor imaging (DTI) and resting-state functional MRI (rs-fMRI) data from 32 children with ADHD-C and 32 group-matched controls were involved. Network-based statistic analysis of the rs-fMRI data revealed a disconnected functional network between the sgACC and multiple regions in the occipital lobe and cerebellum, whereas the DTI data showed disrupted white matter integrity in the subgenual cingulum bundle (sgCB). Post hoc region of interest (ROI)-based analyses showed significantly increased fluctuation of the spontaneous brain activity in the sgACC and higher radial diffusivity in the sgCB in the ADHD group. Both the rs-fMRI and DTI ROI-based measures were significantly correlated with clinical measures that examine behavioral capacities of attention and inhibitory control. Findings of this study suggest that functional alterations in the sgACC and white matter under development in the sgCB may impact each other, and together contribute to impaired attention and inhibitory control function in children with ADHD.

Diffusion tensor imaging tractography study in bipolar disorder patients compared to first-degree relatives and healthy controls

AIM

We aimed to compare white matter structural changes in specific tracts by diffusion tensor imaging (DTI) tractography in patients with bipolar disorder (BD) I, non-ill first-degree relatives (FDR) of the patients, and healthy controls (HC).

METHODS

In a cross-sectional study, we studied right-handed subjects consisting of 16 euthymic BD I patients, 15 FDR, and 15 HC. The anterior thalamic radiation, uncinate fasciculus, corpus callosum, and cingulum bundle were reconstructed by DTI tractography. Mean fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were compared for group differences followed by post-hoc analysis.

RESULTS

The three groups did not differ in terms of sociodemographic variables. There were significant group differences in the FA values among the BD I patients, their FDR, and the HC for the corpus callosum, the dorsal part of the right cingulum bundle, the hippocampal part of the cingulum bundle bilaterally, and the uncinate fasciculus (P < 0.001). The FA values in the patients were significantly lower than in controls, and FDR also showed similar differences; however, they were smaller than those in patients. No significant difference was found between the groups for FA values of the dorsal part of the left cingulum bundle and anterior thalamic radiation. Significant differences were present for ADC values among the groups for the corpus callosum, the dorsal and hippocampal parts of the cingulum, anterior thalamic radiation, and uncinate fasciculus bilaterally (P < 0.01). The FA and ADC values did not correlate significantly with age or any clinical variables.

CONCLUSION

These findings suggest that BD patients and their FDR show alterations in microstructural integrity of white matter tracts, compared to the healthy population.

Psychoradiology: The Frontier of Neuroimaging in Psychiatry

Unlike neurologic conditions, such as brain tumors, dementia, and stroke, the neural mechanisms for all psychiatric disorders remain unclear. A large body of research obtained with structural and functional magnetic resonance imaging, positron emission tomography/single photon emission computed tomography, and optical imaging has demonstrated regional and illness-specific brain changes at the onset of psychiatric disorders and in individuals at risk for such disorders. Many studies have shown that psychiatric medications induce specific measurable changes in brain anatomy and function that are related to clinical outcomes. As a result, a new field of radiology, termed psychoradiology, seems primed to play a major clinical role in guiding diagnostic and treatment planning decisions in patients with psychiatric disorders. This article will present the state of the art in this area, as well as perspectives regarding preparations in the field of radiology for its evolution. Furthermore, this article will (a) give an overview of the imaging and analysis methods for psychoradiology; (b) review the most robust and important radiologic findings and their potential clinical value from studies of major psychiatric disorders, such as depression and schizophrenia; and (c) describe the main challenges and future directions in this field. An ongoing and iterative process of developing biologically based nomenclatures with which to delineate psychiatric disorders and translational research to predict and track response to different therapeutic drugs is laying the foundation for a shift in diagnostic practice in psychiatry from a psychologic symptom-based approach to an imaging-based approach over the next generation. This shift will require considerable innovations for the acquisition, analysis, and interpretation of brain images, all of which will undoubtedly require the active involvement of radiologists. ^© RSNA, 2016 Online supplemental material is available for this article.

Longitudinal differences in white matter integrity in youth at high familial risk for bipolar disorder

OBJECTIVES

Previous neuroimaging studies have reported abnormalities in white matter (WM) pathways in subjects at high familial risk of mood disorders. In the current study, we examined the trajectory of these abnormalities during the early stages of illness development using longitudinal diffusion tensor imaging (DTI) data.

METHODS

Subjects (16-28 years old) were recruited in the Scottish Bipolar Family Study, a prospective longitudinal study that has examined individuals at familial risk of mood disorder on three occasions, 2 years apart. The current study concerns imaging data from the first and second assessments. We analysed DTI data for 43 controls and 69 high-risk individuals who were further subdivided into a group of 53 high-risk subjects who remained well (high-risk well) and 16 who met diagnostic criteria for major depressive disorder (high-risk MDD) at follow-up. Longitudinal differences in fractional anisotropy (FA) between groups based on diagnostic status were investigated using the tract-based spatial statistics technique (TBSS).

RESULTS

We found a significant reduction in FA (P_corr <.05) across widespread brain regions over 2 years in all three groups. The trajectory of FA reduction did not differ significantly between groups.

CONCLUSIONS

These results suggest that there are similar trajectories of FA reductions for controls and high-risk young adults, despite high-risk individuals being at a disadvantaged starting point considering their reduced WM integrity detected at baseline in previous studies. Difference in WM integrity between high-risk individuals and controls could therefore occur in earlier childhood and be a necessary but not sufficient condition to develop future mood disorders.

The role of speed in ADHD-related working memory deficits: A time-based resource-sharing and diffusion model account

Several recent commentaries suggest that, for psychological science to move beyond "homuncular" explanations for cognitive control, it is critically important to examine the role of basic and computationally well-defined processes (e.g. cognitive processing speed). Correlational evidence has previously linked slow speed to working memory (WM) deficits in ADHD, but the directionality of this relationship has not been investigated experimentally and the mechanisms through which speed may influence WM are unclear. Herein, we demonstrate in school-aged children with and without ADHD, that manipulating speed (indexed with the diffusion model) within a WM paradigm reduces WM capacity due to an increase in cognitive load, in a manner that is consistent with predictions of the time-based resource-sharing model of WM. Results suggest slow speed is a plausible cause of WM deficits in ADHD, provide a mechanistic account of this relationship, and urge the exploration of non-executive neurocognitive processes in clinical research on etiology.

Weak functional connectivity in the human fetal brain prior to preterm birth

It has been suggested that neurological problems more frequent in those born preterm are expressed prior to birth, but owing to technical limitations, this has been difficult to test in humans. We applied novel fetal resting-state functional MRI to measure brain function in 32 human fetuses in utero and found that systems-level neural functional connectivity was diminished in fetuses that would subsequently be born preterm. Neural connectivity was reduced in a left-hemisphere pre-language region, and the degree to which connectivity of this left language region extended to right-hemisphere homologs was positively associated with the time elapsed between fMRI assessment and delivery. These results provide the first evidence that altered functional connectivity in the preterm brain is identifiable before birth. They suggest that neurodevelopmental disorders associated with preterm birth may result from neurological insults that begin in utero.