Diffusion tensor imaging in psychiatric disorders. Top Magn Reson Imaging. 2008;19:97-109. [PMID: 19363432 DOI: 10.1097/rmr.0b013e3181809f1e]

Distinct White Matter Fiber Density Patterns in Bipolar and Depressive Disorders: Insights from Fixel-Based Analysis

Background

Differentiating Bipolar (BD) and depressive (DD) disorders remains challenging in clinical practice due to overlapping symptoms. Our study employs fixel-based analysis (FBA) to examine fiber-specific white matter differences in BD and DD and gain insights into the ability of FBA metrics to predict future spectrum mood symptoms.

Methods

163 individuals between 18 and 45 years with BD, DD, and healthy controls (HC) underwent Diffusion Magnetic Resonance Imaging. FBA was used to assess fiber density (FD), fiber cross-section (FC), and fiber density cross-section (FDC) in major white matter tracts. A longitudinal follow-up evaluated whether FBA measures predicted future spectrum depressive and hypomanic symptom trajectories over six months.

Results

Direct comparisons between BD and DD indicated lower FD in the right superior longitudinal and uncinate fasciculi and left thalamo-occipital tract in BD versus DD. Individuals with DD exhibited lower FD in the left arcuate fasciculus than those with BD. Compared to HC, both groups showed lower FD in the splenium of the corpus callosum and left striato-occipital and optic radiation tracts. FD in these tracts predicted future spectrum symptom severity. Exploratory analyses revealed associations between FD, medication use, and marijuana exposure.

Conclusions

Our findings highlight distinct and overlapping white matter alterations in BD and DD. Furthermore, FD in key tracts may serve as a predictor of future symptom trajectories, supporting the potential clinical utility of FD as a biomarker for mood disorder prognosis. Future longitudinal studies are needed to explore the impact of treatment and disease progression on white matter microstructure.

Association between white matter microstructural changes and aggressiveness. A case-control diffusion tensor imaging study

Research has focused on identifying neurobiological risk factors associated with aggressive behavior in order to improve prevention and treatment efforts. This study aimed to characterize microstructural differences in white matter (WM) integrity in individuals prone to aggression. We hypothesized that altered cerebral WM microstructure may underlie normal individual variability in aggression and tested this using a case-control design in healthy individuals. Diffusion tensor imaging (DTI) was used to examine WM changes in martial artists (n = 29) and age-matched controls (n = 31). We performed tract-based spatial statistics (TBSS) to identify differences in axial diffusivity (AD), fractional anisotropy (FA) and mean diffusivity (MD) between the two groups at the whole-brain level. Martial artists were significantly more aggressive than controls, with increased MD in parietal and occipital areas and increased AD in widespread fiber tracts in the frontal, parietal and temporal areas. Positive associations between AD/MD and (physical) appetitive aggression were identified in several clusters, including the corpus callosum, the superior longitudinal fasciculus and the corona radiata. Our study found evidence for WM microstructural changes associated with aggressiveness in a community case-control sample. Longitudinal studies with larger cohorts, taking into account the dimensional nature of aggressiveness, are needed to better understand the underlying neurobiology.

Neuroimaging and the Investigation of Drug-Drug Interactions Involving Psychedelics

Psychedelic therapies are an emerging class of treatments in psychiatry with great potential, however relatively little is known about their interactions with other commonly used psychiatric medications. As psychedelic therapies become more widespread and move closer to the clinic, they likely will need to be integrated into existing treatment models which may include one or more traditional pharmacological therapies, meaning an awareness of potential drug-drug interactions will become vital. This commentary outlines some of the issues surrounding the study of drug-drug interactions of this type, provides a summary of some of the relevant key results to date, and charts a way forward which relies crucially on multimodal neuroimaging investigations. Studies in humans which combine Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging (fMRI), plus ancillary measures, are likely to provide the most comprehensive assessment of drug-drug interactions involving psychedelics and the relevant effects at multiple levels of the drug response (molecular, functional, and clinical).

Urban environment during pregnancy and childhood and white matter microstructure in preadolescence in two European birth cohorts

Growing evidence suggests that urban environment may influence cognition and behavior in children, but the underlying pollutant and neurobiological mechanisms are unclear. We evaluated the association of built environment and urban natural space indicators during pregnancy and childhood with brain white matter microstructure in preadolescents, and examined the potential mediating role of air pollution and road-traffic noise. We used data of the Generation R Study, a population-based birth cohort in Rotterdam, the Netherlands (n = 2725; 2002-2006) for the primary analyses. Replication of the main findings was attempted on an independent neuroimaging dataset from the PELAGIE birth cohort, France (n = 95; 2002-2006). We assessed exposures to 12 built environment and 4 urban natural spaces indicators from conception up to 9 years of age. We computed 2 white matter microstructure outcomes (i.e., average of fractional anisotropy (FA) and mean diffusivity (MD) from 12 white matte tracts) from diffusion tensor imaging data. Greater distance to the nearest major green space during pregnancy was associated with higher whole-brain FA (0.001 (95%CI 0.000; 0.002) per 7 m increase), and higher land use diversity during childhood was associated with lower whole-brain MD (-0.001 (95%CI -0.002; -0.000) per 0.12-point increase), with no evidence of mediation by air pollution nor road-traffic noise. Higher percentage of transport and lower surrounding greenness during pregnancy were associated with lower whole-brain FA, and road-traffic noise mediated 19% and 52% of these associations, respectively. We found estimates in the same direction in the PELAGIE cohort, although confidence intervals were larger and included the null. This study suggests an association between urban environment and white matter microstructure, mainly through road-traffic noise, indicating that greater access to green space nearby might promote white matter development.

Longitudinal Associations Between White Matter Microstructure and Psychiatric Symptoms in Youth

OBJECTIVE

Associations between psychiatric problems and white matter (WM) microstructure have been reported in youth. Yet, a deeper understanding of this relation has been hampered by a dearth of well-powered longitudinal studies and a lack of explicit examination of the bidirectional associations between brain and behavior. We investigated the temporal directionality of WM microstructure and psychiatric symptom associations in youth.

METHOD

In this observational study, we leveraged the world's largest single- and multi-site cohorts of neurodevelopment: the Generation R (GenR) and Adolescent Brain Cognitive Development Studies (ABCD) (total n scans = 11,400; total N = 5,700). We assessed psychiatric symptoms with the Child Behavioral Checklist as broad-band internalizing and externalizing scales, and as syndrome scales (eg, Anxious/Depressed). We quantified WM with diffusion tensor imaging (DTI), globally and at a tract level. We used cross-lagged panel models to test bidirectional associations of global and specific measures of psychopathology and WM microstructure, meta-analyzed results across cohorts, and used linear mixed-effects models for validation.

RESULTS

We did not identify any longitudinal associations of global WM microstructure with internalizing or externalizing problems across cohorts (confirmatory analyses) before, and after multiple testing corrections. We observed similar findings for longitudinal associations between tract-based microstructure with internalizing and externalizing symptoms, and for global WM microstructure with specific syndromes (exploratory analyses). Some cross-sectional associations surpassed multiple testing corrections in ABCD, but not in GenR.

CONCLUSION

Uni- or bi-directionality of longitudinal associations between WM and psychiatric symptoms were not robustly identified. We have proposed several explanations for these findings, including interindividual differences, the use of longitudinal approaches, and smaller effects than expected.

STUDY REGISTRATION INFORMATION

Bidirectionality Brain Function and Psychiatric Symptoms; https://doi.org/10.17605/OSF.IO/PNY92.

White matter microstructure and connectivity changes after surgery in male adults with obstructive sleep apnea: recovery or reorganization?

Study objectives

Obstructive sleep apnea (OSA) is a prevalent clinical problem significantly affecting cognitive functions. Surgical treatment is recommended for those unable to use continuous positive airway pressure. We aimed to investigate the therapeutic effect of upper airway surgery on the white matter (WM) microstructure and brain connectivity in patients with OSA.

Methods

Twenty-one male patients with moderate-to-severe OSA were recruited for multi-level upper airway surgery. Overnight polysomnography (PSG), neuropsychiatric tests, and brain MRI scans were acquired before and 6.1 ± 0.8 months after surgery. Nineteen male patients with untreated OSA were also included as a reference group. We calculated the longitudinal changes of diffusion tensor imaging (DTI) parameters, including fractional anisotropy (ΔFA) and mean/axial/radial diffusivity (ΔMD/AD/RD). We also assessed changes in network properties based on graph theory.

Results

Surgically treated patients showed improvement in PSG parameters and verbal memory after surgery. Globally, ΔFA was significantly higher and ΔRD was lower in the surgery group than in the untreated group. Especially ΔFA of the tracts involved in the limbic system was higher after surgery. In network analysis, higher Δbetweenness and lower Δclustering coefficients were observed in the surgical group than in the untreated group. Finally, the improvement of verbal memory after surgery positively correlated with ΔFA in superior thalamic radiation (p = 0.021), fronto aslant tracts (p = 0.027), and forceps minor tracts (p = 0.032).

Conclusion

Surgical treatment of OSA can alleviate alterations in WM integrity and disruptions in local networks, particularly for the tracts involved in the limbic system. These findings may further explain the cognitive improvement observed after the treatment of OSA.

Different degrees of nodes behind obsessive-compulsive symptoms of schizophrenia

Obsessive-compulsive symptoms are frequently observed in various psychiatric disorders, including obsessive-compulsive disorder, schizophrenia, depression, and anxiety. However, the underlying anatomical basis of these symptoms remains unclear. In this study, we aimed to investigate the mechanism of schizophrenia with obsessive-compulsive symptoms by using diffusion tensor imaging (DTI)-based structural brain connectivity analysis to assess the network differences between patients with obsessive-compulsive disorder (OCD), patients with schizophrenia showing obsessive-compulsive symptoms (SCH), schizophrenia patients with obsessive-compulsive symptoms due to clozapine (LDP), and healthy controls (CN). We included 21 patients with OCD, 20 patients with SCH, 12 patients with LDP, and 25 CN. All subjects underwent MRI scanning, and structural brain connections were estimated using diffusion tensor imaging for further analysis of brain connectivity. The topology and efficiency of the network and the characteristics of various brain regions were investigated. We assessed baseline YALE-BROWN OBSESSIVE COMPULSIVE SCALE (Y-BOCS), Positive and Negative Syndrome Scale (PANSS), and 24-item Hamilton Depression Scale (HAMD-24) scores. Our results showed significant differences among the SCH, OCD, and CN groups (p < 0.05) in the MRI-measured degree of the following nodes: the superior orbitofrontal gyrus (25Frontal_Med_Orb_L), lingual gyrus (47Lingual_L), postcentral gyrus (58Postcentral_R), and inferior temporal gyrus (90Temporal_Inf_R). Additionally, we found significant differences in the degree of the brain regions 02Precentral_R, 47Lingual_L, 58Postcentral_R, and 90Temporal_Inf_R between the CN, OCD, SCH, and LDP groups (p < 0.05). These findings suggest that alterations in the degree of nodes might be the mechanism behind obsessive-compulsive symptoms in schizophrenia.

Structural Connectomes of COVID-Survivors Show Disruption in Global Integration and Small-Worldness

Even after recovery from the COVID-19 infection, there have been a multitude of cases reporting post-COVID neurological symptoms including memory loss, brain fog, and attention deficit. Many studies have observed localized microstructural damages in the white matter regions of COVID survivors, indicating potential damage to the axonal pathways in the brain. Therefore, in this study, we have investigated the global impact of localized damage to white matter tracts using graph theoretical analysis of the structural connectome of 45 COVID-recovered subjects and 30 Healthy Controls (HCs). We have implemented Diffusion Tensor Imaging based reconstruction followed by deterministic tractography to extract structural connections among different regions of the brain. Interpreting this structural connectivity as weighted undirected graphs, we have used graph theoretical measures like global efficiency, characteristic path length (CPL), clustering coefficient (CC), modularity, Fiedler value, and assortativity coefficient to quantify the global integration, segregation, and robustness of the brain networks. We statistically compare the cohorts based on these graph measures by employing permutation testing for 100,000 permutations. Post multiple comparisons error correction, we find that the COVID-recovered cohort shows a reduction in global efficiency and CC while they exhibit higher modularity and CPL. This disruption of the balance between global integration and segregation indicates the loss of small-world property in COVID survivors' connectomes which has been linked with other disorders such as cognitive impairment and Alzheimer's. Overall, our study sheds light on the alterations in structural connectivity and its role in post-COVID symptoms.

Disrupted structural connectivity and less efficient network system in patients with the treatment-naive adult attention-deficit/hyperactivity disorder

Introduction

Attention-deficit/hyperactivity disorder (ADHD) is a neuropsychiatric disorder whose primary symptoms are hyperactivity, impulsivity, and inattention. Historically, ADHD was recognized as a disease of childhood and adolescence. However, many patients are known to have persistent symptoms into adulthood. Many researchers consider the neuropathology of ADHD to be based on abnormalities in multiple parallel and intersecting pathways rather than a single anatomical area, but such alterations remain to be clarified.

Methods

Using diffusion tensor imaging, we investigated differences in the global network metrics estimated by graph theory and the degree of connectivity between adjacent voxels within a white matter (WM) fascicle defined by the density of the diffusing spins (connectometry) between 19 drug-naive Japanese patients with adult ADHD and 19 matched healthy controls (HCs). In adult patients with ADHD, we examined the relationships between the symptomatology of ADHD and global network metrics and WM abnormalities.

Results

Compared with HCs, adult patients with ADHD showed a reduced rich-club coefficient and decreased connectivity in widely distributed WMs such as the corpus callosum, the forceps, and the cingulum bundle. Correlational analyses demonstrated that the general severity of ADHD symptoms was associated with several global network metrics, such as lower global efficiency, clustering coefficient, small worldness, and longer characteristic path length. The connectometry revealed that the severity of hyperactive/impulsive symptoms was associated with overconnectivity in the corticostriatal, corticospinal, and corticopontine tracts, the inferior fronto-occipital fasciculus, and the extreme capsule but dysconnectivity in the cerebellum. The severity of inattentive symptoms was associated with dysconnectivity in the intracerebellar circuit and some other fibers.

Conclusion

The results of the present study indicated that patients with treatment-naive adult ADHD showed disrupted structural connectivity, which contributes to less efficient information transfer in the ADHD brain and pathophysiology of ADHD.

Trial registration

UMIN Clinical Trials Registry (UMIN-CTR) UMIN000025183, Registered: 5 January 2017.

Air pollution, white matter microstructure, and brain volumes: Periods of susceptibility from pregnancy to preadolescence

Air pollution exposure during early-life is associated with altered brain development, but the precise periods of susceptibility are unknown. We aimed to investigate whether there are periods of susceptibility of air pollution between conception and preadolescence in relation to white matter microstructure and brain volumes at 9-12 years old. We used data of 3515 children from the Generation R Study, a population-based birth cohort from Rotterdam, the Netherlands (2002-2006). We estimated daily levels of nitrogen dioxide (NO2), and particulate matter (PM2.5 and PM2.5absorbance) at participants' homes during pregnancy and childhood using land-use regression models. Diffusion tensor and structural brain images were obtained when children were 9-12 years of age, and we calculated fractional anisotropy and mean diffusivity, and several brain structure volumes. We performed distributed lag non-linear modeling adjusting for socioeconomic and lifestyle characteristics. We observed specific periods of susceptibility to all air pollutants from conception to age 5 years in association with lower fractional anisotropy and higher mean diffusivity that survived correction for multiple testing (e.g., -0.85 fractional anisotropy (95%CI -1.43; -0.27) per 5 μg/m³ increase in PM2.5 between conception and 4 years of age). We also observed certain periods of susceptibility to some air pollutants in relation to global brain and some subcortical brain volumes, but only the association between PM2.5 and putamen survived correction for multiple testing (172 mm³ (95%CI 57; 286) per 5 μg/m³ increase in PM2.5 between 4 months and 1.8 year of age). This study suggested that conception, pregnancy, infancy, toddlerhood, and early childhood seem to be susceptible periods to air pollution exposure for the development of white matter microstructure and the putamen volume. Longitudinal studies with repeated brain outcome measurements are needed for understanding the trajectories and the long-term effects of exposure to air pollution.

Antenatal Dexamethasone Treatment Induces Sex-dependent Upregulation of NTPDase1/CD39 and Ecto-5'-nucleotidase/CD73 in the Rat Fetal Brain

Dexamethasone (DEX) is frequently used to treat women at risk of preterm delivery, but although indispensable for the completion of organ maturation in the fetus, antenatal DEX treatment may exert adverse sex-dimorphic neurodevelopmental effects. Literature findings implicated oxidative stress in adverse effects of DEX treatment. Purinergic signaling is involved in neurodevelopment and controlled by ectonucleotidases, among which in the brain the most abundant are ectonucleoside triphosphate diphosphohydrolase 1 (NTPDase1/CD39) and ecto-5'-nucleotidase (e5'NT/CD73), which jointly dephosphorylate ATP to adenosine. They are also involved in cell adhesion and migration, processes integral to brain development. Upregulation of CD39 and CD73 after DEX treatment was reported in adult rat hippocampus. We investigated the effects of maternal DEX treatment on CD39 and CD73 expression and enzymatic activity in the rat fetal brain of both sexes, in the context of oxidative status of the brain tissue. Fetuses were obtained at embryonic day (ED) 21, from Wistar rat dams treated with 0.5 mg DEX/kg/day, at ED 16, 17, and 18, and brains were processed and used for further analysis. Sex-specific increase in CD39 and CD73 expression and in the corresponding enzyme activities was induced in the brain of antenatally DEX-treated fetuses, more prominently in males. The oxidative stress induction after antenatal DEX treatment was confirmed in both sexes, although showing a slight bias in males. Due to the involvement of purinergic system in crucial neurodevelopmental processes, future investigations are needed to determine the role of these observed changes in the adverse effects of antenatal DEX treatment.

Structural and Functional Default Mode Network Connectivity and Antipsychotic Treatment Response in Medication-Naïve First Episode Psychosis Patients

Introduction

Only a few studies have comprehensively characterized default mode network (DMN) pathology on a structural and functional level, and definite conclusions cannot be drawn due to antipsychotic medication exposure and illness chronicity. The objective of this study was to characterize DMN pathology in medication-naïve first episode psychosis (FEP) patients, and determine if DMN structural and functional connectivity (FC) have potential utility as a predictor for subsequent antipsychotic treatment response.

Methods

Diffusion imaging and resting state FC data from 42 controls and 52 FEP were analyzed. Patients then received 16 weeks of antipsychotic treatment. Using region of interest analyses, we quantified FC of the DMN and structural integrity of the white matter tracts supporting DMN function. We then did linear regressions between DMN structural and FC indices and antipsychotic treatment response.

Results

We detected reduced DMN fractional anisotropy and axial diffusivity in FEP compared to controls. No DMN FC abnormalities nor correlations between DMN structural and FC were found. Finally, DMN fractional anisotropy and radial diffusivity were associated with response to treatment.

Conclusion

Our study highlights the critical role of the DMN in the pathophysiology suggesting that axonal damage may already be present in FEP patients. We also demonstrated that DMN pathology is clinically relevant, as greater structural DMN alterations were associated with a less favorable clinical response to antipsychotic medications.

Cortical connectivity in the face of congenital structural changes-A case of homozygous LAMC3 mutation

The homozygous LAMC3 gene mutation is associated with severe bilateral smoothening and thickening of the lateral occipital cortex . Despite this and further significant changes in gray matter structure, a patient harboring this mutation exhibited a range of remarkably intact perceptual abilities . One possible explanation of this perceptual sparing could be that the white matter structural integrity and functional connectivity in relevant pathways remained intact. To test this idea, we used diffusion tensor and functional magnetic resonance imaging to investigate functional connectivity in resting-state networks in major structural pathways involved in object perception and visual attention and corresponding microstructural integrity in a patient with homozygous LAMC3 mutation and sex, age, education, and socioeconomically matched healthy control group. White matter microstructural integrity results indicated widespread disruptions in both intra- and interhemispheric structural connections except inferior longitudinal fasciculus. With a few exceptions, the functional connectivity between the patient's adjacent gray matter regions of major white matter tracts of interest was conserved. In addition, functional localizers for face, object, and place areas showed similar results with a representative control, providing an explanation for the patient's intact face, place, and object recognition abilities. To generalize this finding, we also compared functional connectivity between early visual areas and face, place, and object category-selective areas, and we found that the functional connectivity of the patient was not different from the control group. Overall, our results provided complementary information about the effects of LAMC3 gene mutation on the human brain including intact temporo-occipital structural and functional connectivity that are compatible with preserved perceptual abilities.

White matter and neurite morphology differ in psychogenic nonepileptic seizures

OBJECTIVE

To further evaluate the relationship between the clinical profiles and limbic and motor brain regions and their connecting pathways in psychogenic nonepileptic seizures (PNES). Neurite Orientation Dispersion and Density Indices (NODDI) multicompartment modeling was used to test the relationships between tissue alterations in patients with traumatic brain injury (TBI) and multiple psychiatric symptoms.

METHODS

The sample included participants with prior TBI (TBI; N = 37) but no PNES, and with TBI and PNES (TBI + PNES; N = 34). Participants completed 3T Siemens Prisma MRI high angular resolution imaging diffusion protocol. Statistical maps, including fractional anisotropy (FA), mean diffusivity (MD), neurite dispersion [orientation dispersion index (ODI)] and density [intracellular volume fraction (ICVF), and free water (i.e., isotropic) volume fraction (V-ISO)] signal intensity, were generated for each participant. Linear mixed-effects models identified clusters of between-group differences in indices of white matter changes. Pearson's r correlation tests assessed any relationship between signal intensity and psychiatric symptoms.

RESULTS

Compared to TBI, TBI + PNES revealed decreases in FA, ICVF, and V-ISO and increases in MD for clusters within cingulum bundle, uncinate fasciculus, fornix/stria terminalis, and corticospinal tract pathways (cluster threshold α = 0.05). Indices of white matter changes for these clusters correlated with depressive, anxiety, PTSD, psychoticism, and somatization symptom severity (FDR threshold α = 0.05). A follow-up within-group analysis revealed that these correlations failed to reach the criteria for significance in the TBI + PNES group alone.

INTERPRETATION

The results expand support for the hypothesis that alterations in pathways comprising the specific PNES network correspond to patient profiles. These findings implicate myelin-specific changes as possible contributors to PNES, thus introducing novel potential treatment targets.

Comparative Neuropsychiatry: White Matter Abnormalities in Children and Adolescents with Schizophrenia, Bipolar Affective Disorder, and Obsessive-Compulsive Disorder

Background:

There is considerable evidence that white matter abnormalities play a key role in the pathogenesis of a number of major psychiatric disorders, including schizophrenia, bipolar affective disorder, and obsessive-compulsive disorder. Few studies, however, have compared white matter abnormalities early in the course of the illness.

Methods:

A total of 102 children and adolescents participated in the study, including 43 with early-onset schizophrenia, 13 with early-onset bipolar affective disorder, 17 with obsessive-compulsive disorder, and 29 healthy controls. Diffusion tensor imaging scans were obtained on all children and the images were assessed for the presence of non-spatially overlapping regions of white matter differences, a novel algorithm known as the pothole approach.

Results:

Patients with early-onset schizophrenia and early-onset bipolar affective disorder had a significantly greater number of white matter potholes compared to controls, but the total number of potholes did not differ between the two groups. The volumes of the potholes were significantly larger in patients with early-onset bipolar affective disorder compared to the early-onset schizophrenia group. Children and adolescents with obsessive-compulsive disorder showed no differences in the total number of white matter potholes compared to controls.

Conclusions:

White matter abnormalities in early-onset schizophrenia and bipolar affective disorder are more global in nature, whereas children and adolescents with obsessive-compulsive disorder do not show widespread differences in FA.

Neuroimaging Biomarkers for Predicting Treatment Response and Recurrence of Major Depressive Disorder

The acute treatment duration for major depressive disorder (MDD) is 8 weeks or more. Treatment of patients with MDD without predictors of treatment response and future recurrence presents challenges and clinical problems to patients and physicians. Recently, many neuroimaging studies have been published on biomarkers for treatment response and recurrence of MDD using various methods such as brain volumetric magnetic resonance imaging (MRI), functional MRI (resting-state and affective tasks), diffusion tensor imaging, magnetic resonance spectroscopy, near-infrared spectroscopy, and molecular imaging (i.e., positron emission tomography and single photon emission computed tomography). The results have been inconsistent, and we hypothesize that this could be due to small sample size; different study design, including eligibility criteria; and differences in the imaging and analysis techniques. In the future, we suggest a more sophisticated research design, larger sample size, and a more comprehensive integration including genetics to establish biomarkers for the prediction of treatment response and recurrence of MDD.

Exposure to Air Pollution during Pregnancy and Childhood, and White Matter Microstructure in Preadolescents

BACKGROUND

Air pollution has been related to brain structural alterations, but a relationship with white matter microstructure is unclear.

OBJECTIVES

We assessed whether pregnancy and childhood exposures to air pollution are related to white matter microstructure in preadolescents.

METHODS

We used data of 2,954 children from the Generation R Study, a population-based birth cohort from Rotterdam, Netherlands (2002-2006). Concentrations of 17 air pollutants including nitrogen oxides (NOX), particulate matter (PM), and components of PM were estimated at participants' homes during pregnancy and childhood using land-use regression models. Diffusion tensor images were obtained at child's 9-12 years of age, and fractional anisotropy (FA) and mean diffusivity (MD) were computed. We performed linear regressions adjusting for socioeconomic and lifestyle characteristics. Single-pollutant analyses were followed by multipollutant analyses using the Deletion/Substitution/Addition (DSA) algorithm.

RESULTS

In the single-pollutant analyses, higher concentrations of several air pollutants during pregnancy or childhood were associated with significantly lower FA or higher MD (p<0.05). In multipollutant models of pregnancy exposures selected by DSA, higher concentration of fine particles was associated with significantly lower FA [-0.71 (95% CI: -1.26, -0.16) per 5 μg/m3 fine particles] and higher concentration of elemental silicon with significantly higher MD [0.06 (95% CI: 0.01, 0.11) per 100 ng/m3 silicon]. Multipollutant models of childhood exposures selected by DSA indicated significant associations of NOX with FA [-0.14 (95% CI: -0.23, -0.04) per 20-μg/m3 NOX increase], and of elemental zinc and the oxidative potential of PM with MD [0.03 (95% CI: 0.01, 0.04) per 10-ng/m3 zinc increase and 0.07 (95% CI: 0.00, 0.44) per 1-nmol DTT/min/m3 oxidative potential increase]. Mutually adjusted models of significant exposures during pregnancy and childhood indicated significant associations of silicon during pregnancy, and zinc during childhood, with MD.

DISCUSSION

Exposure in pregnancy and childhood to air pollutants from tailpipe and non-tailpipe emissions were associated with lower FA and higher MD in white matter of preadolescents. https://doi.org/10.1289/EHP4709.

White Matter Measures and Cognition in Schizophrenia

White matter (WM) abnormalities are commonly reported in schizophrenia but whether these arise from the axon or myelin compartments or both is not known. In addition, the relationship between WM abnormalities and cognitive function is not fully explored in this condition. We recruited 39 individuals with schizophrenia spectrum disorders and 37 healthy comparison subjects. All participants underwent MRI scanning at 4 Tesla to collect data in the prefrontal white matter on magnetization transfer ratio (MTR) and diffusion tensor spectroscopy (DTS) which provide information on myelin and axon compartments, respectively. We also collected Matrics Composite Cognitive Battery (MCCB) and Stroop cognitive data. We found an elevated N-acetylaspartate (NAA) apparent diffusion coefficient in schizophrenia in this cohort as in our previous work; we also observed poorer performance on both the MCCB composite and the Stroop in schizophrenia patients compared to controls. The MTR measure was correlated with the MCCB composite (r = 0.363, p = 0.032) and Stroop scores (r = 0.387, p = 0.029) in healthy individuals but not in schizophrenia. Since this is the first exploration of the relationship between these WM and cognitive measures, we consider our analyses exploratory and did not adjust for multiple comparisons; the findings are not statistically significant if adjusted for multiple comparisons. These findings indicate that WM integrity is associated with cognitive function in healthy individuals but this relationship breaks down in patients with schizophrenia.

Brain structure and internalizing and externalizing behavior in typically developing children and adolescents

Mental health problems often emerge in adolescence and are associated with reduced gray matter thickness or volume in the prefrontal cortex (PFC) and limbic system and reduced fractional anisotropy (FA) and increased mean diffusivity (MD) of white matter linking these regions. However, few studies have investigated whether internalizing and externalizing behavior are associated with brain structure in children and adolescents without mental health disorders, which is important for understanding the progression of symptoms. 67 T1-weighted and diffusion tensor imaging datasets were obtained from 48 typically developing participants aged 6-16 years (37M/30F; 19 participants had two visits). Volume was calculated in the prefrontal and limbic structures, and diffusion parameters were assessed in limbic white matter. Linear mixed effects models were used to compute associations between brain structure and internalizing and externalizing behavior, assessed using the Behavioral Assessment System for Children (BASC-2) Parent Rating Scale. Internalizing behavior was positively associated with MD of the bilateral cingulum. Gender interactions were found in the cingulum, with stronger positive relationships between MD and internalizing behavior in females. Externalizing behavior was negatively associated with FA of the left cingulum, and the left uncinate fasciculus showed an age-behavior interaction. No relationships between behavior and brain volumes survived multiple comparison correction. These results show altered limbic white matter FA and MD related to sub-clinical internalizing and externalizing behavior and further our understanding of neurological markers that may underlie risk for future mental health disorders.

Brain Development and Stochastic Processes During Prenatal and Early Life: You Can't Lose It if You've Never Had It; But It's Better to Have It and Lose It, Than Never to Have Had It at All

Brain development, although largely driven by genetic processes, also is influenced by environmental factors. However, there has been little discussion in the psychiatric literature on the role of stochastic, or chance, events that take place during neurodevelopment. Studies suggest that the brain capitalizes on and regulates the extent of stochastic processes during development. Furthermore, because neurodevelopment is influenced by environmental factors, there is emerging evidence that fostering those positive environmental factors during prenatal and early life could optimize neurodevelopment and provide greater resilience, including those potentially resulting from stochastic processes. Evidence for the role of environmental factors in optimizing early brain development is supported by work in large population-based studies of child development, randomized control trials in high-risk populations, and early-life adoption studies. The public health message is that creating an environment that fosters optimal brain development during prenatal and early life could prevent psychopathology and provide the developing brain the best chance against negative stochastic processes and potential stressors that are inevitable later in life.

Antisocial behavior with callous-unemotional traits is associated with widespread disruptions to white matter structural connectivity among low-income, urban males

Antisocial behavior (AB), including violence, criminality, and substance abuse, is often linked to deficits in emotion processing, reward-related learning, and inhibitory control, as well as their associated neural networks. To better understand these deficits, the structural connections between brain regions implicated in AB can be examined using diffusion tensor imaging (DTI), which assesses white matter microstructure. Prior studies have identified differences in white matter microstructure of the uncinate fasciculus (UF), primarily within offender samples. However, few studies have looked beyond the UF or determined whether these relationships are present dimensionally across the range of AB and callous-unemotional (CU) traits. In the current study, we examined associations between AB and white matter microstructure from major fiber tracts, including the UF. Further, we explored whether these associations were specific to individuals high on CU traits. Within a relatively large community sample of young adult men from low-income, urban families (N = 178), we found no direct relations between dimensional, self-report measures of either AB or CU traits and white matter microstructure. However, we found significant associations between AB and white matter microstructure of several tracts only for those with high co-occurring levels of CU traits. In general, these associations did not differ according to race, socioeconomic status, or comorbid psychiatric symptoms. The current results suggest a unique neural profile of severe AB in combination with CU traits, characterized by widespread differences in white matter microstructure, which differs from either AB or CU traits in isolation and is not specific to hypothesized tracts (i.e., the UF).

A data-driven transdiagnostic analysis of white matter integrity in young adults with major psychiatric disorders

Diffusion tensor imaging (DTI) has been utilized to index white matter (WM) integrity in the major psychiatric disorders. However, the findings within and across such disorders have been mixed. Given this, transdiagnostic sampling with data-driven statistical approaches may lead to new and better insights about the clinical and functional factors associated with WM abnormalities. Thus, we undertook a cross-sectional DTI study of 401 young adult (18-30 years old) outpatients with a major psychiatric (depressive, bipolar, psychotic, or anxiety) disorder and 61 healthy controls. Participants also completed self-report questionnaires and underwent neuropsychological assessment. Fractional anisotropy (FA) as well as axial (AD) and radial (RD) diffusivity was determined via a whole brain voxel-wise approach (tract-based spatial statistics). Hierarchical cluster analysis was performed on FA scores in patients only, obtained from 20 major WM tracts (that is, association, projection and commissural fibers). The three cluster groups derived were distinguished by having consistently increased or decreased FA scores across all tracts. Compared to controls, the largest cluster (N = 177) showed significantly increased FA in 55% of tracts, the second cluster (N = 169) demonstrated decreased FA (in 90% of tracts) and the final cluster (N = 55) exhibited the most increased FA (in 95% of tracts). Importantly, the distribution of primary diagnosis did not significantly differ among the three clusters. Furthermore, the clusters showed comparable functional, clinical and neuropsychological measures, with the exception of alcohol use, medication status and verbal fluency. Overall, this study provides evidence that among young adults with a major psychiatric disorder there are subgroups with either abnormally high or low FA and that either pattern is associated with suboptimal functioning. Importantly, these neuroimaging-based subgroups appear despite diagnostic and clinical factors, suggesting differential treatment strategies are warranted.

A computational network control theory analysis of depression symptoms

Rumination and impaired inhibition are considered core characteristics of depression. However, the neurocognitive mechanisms that contribute to these atypical cognitive processes remain unclear. To address this question, we apply a computational network control theory approach to structural brain imaging data acquired via diffusion tensor imaging in a large sample of participants, to examine how network control theory relates to individual differences in subclinical depression. Recent application of this theory at the neural level is built on a model of brain dynamics, which mathematically models patterns of inter-region activity propagated along the structure of an underlying network. The strength of this approach is its ability to characterize the potential role of each brain region in regulating whole-brain network function based on its anatomical fingerprint and a simplified model of node dynamics. We find that subclinical depression is negatively related to higher integration abilities in the right anterior insula, replicating and extending previous studies implicating atypical switching between the default mode and Executive Control Networks in depression. We also find that subclinical depression is related to the ability to “drive” the brain system into easy to reach neural states in several brain regions, including the bilateral lingual gyrus and lateral occipital gyrus. These findings highlight brain regions less known in their role in depression, and clarify their roles in driving the brain into different neural states related to depression symptoms.

In vivo Diffusion Tensor Imaging, Diffusion Kurtosis Imaging, and Tractography of a Sciatic Nerve Injury Model in Rat at 9.4T

Peripheral nerve injuries result in severe loss of sensory and motor functions in the afflicted limb. There is a lack of standardised models to non-invasively study degeneration, regeneration, and normalisation of neuronal microstructure in peripheral nerves. This study aimed to develop a non-invasive evaluation of peripheral nerve injuries, using diffusion tensor imaging (DTI), diffusion kurtosis imaging (DKI), and tractography on a rat model of sciatic nerve injury. 10 female Sprague Dawley rats were exposed to sciatic nerve neurotmesis and studied using a 9.4 T magnet, by performing DTI and DKI of the sciatic nerve before and 4 weeks after injury. The distal nerve stump showed a decrease in fractional anisotropy (FA), mean kurtosis (MK), axonal water fraction (AWF), and radial and axonal kurtosis (RK, AK) after injury. The proximal stump showed a significant decrease in axial diffusivity (AD) and increase of MK and AK as compared with the uninjured nerve. Both mean diffusivity (MD) and radial diffusivity (RD) increased in the distal stump after injury. Tractography visualised the sciatic nerve and the site of injury, as well as local variations of the diffusion parameters following injury. In summary, the described method detects changes both proximal and distal to the nerve injury.

Cerebral white matter sex dimorphism in alcoholism: a diffusion tensor imaging study

Excessive alcohol consumption is associated with brain aberrations, including abnormalities in frontal and limbic brain regions. In a prior diffusion tensor magnetic resonance imaging (dMRI) study of neuronal circuitry connecting the frontal lobes and limbic system structures, we demonstrated decreases in white matter fractional anisotropy in abstinent alcoholic men. In the present study, we examined sex differences in alcoholism-related abnormalities of white matter connectivity and their association with alcoholism history. The dMRI scans were acquired from 49 abstinent alcoholic individuals (26 women) and 41 nonalcoholic controls (22 women). Tract-based spatial statistical tools were used to estimate regional FA of white matter tracts and to determine sex differences and their relation to measures of alcoholism history. Sex-related differences in white matter connectivity were observed in association with alcoholism: Compared to nonalcoholic men, alcoholic men had diminished FA in portions of the corpus callosum, the superior longitudinal fasciculi II and III, and the arcuate fasciculus and extreme capsule. In contrast, alcoholic women had higher FA in these regions. Sex differences also were observed for correlations between corpus callosum FA and length of sobriety. Our results suggest that sexual dimorphism in white matter microstructure in abstinent alcoholics may implicate underlying differences in the neurobehavioral liabilities for developing alcohol abuse disorders, or for sequelae following abuse.

Failure to Replicate the Association Between Fractional Anisotropy and the Serotonin Transporter Gene (5-HTTLPR, rs25531)

Recent work underlines the importance of alterations in white matter (e.g., measured by fractional anisotropy (FA)) as a neural vulnerability marker for psychiatric disorders. In this context, the uncinate fasciculus (UF), which connects the limbic system with prefrontal areas, has repeatedly been linked to psychiatric disorders, fear processing, and anxiety-related traits. Individual differences in FA may partly be genetically determined. Variation in the promoter region of the serotonin transporter gene (serotonin transporter-linked polymorphic region [5-HTTLPR]) is a particularly promising candidate in this context, which has been linked to psychiatric disorders as well as to limbic and prefrontal reactivity. However, findings on the association between the 5-HTTLPR and FA within the UF-tract have been heterogeneous. The present study investigated this relationship and extended previous work by considering different genetic classification approaches as well as sex effects in a human sample (n = 114). All participants were genotyped for the 5-HTTLPR and the rs25531 polymorphism. As a main result, we did not find any significant relationship between the 5-HTTLPR and FA in the UF-tract although power analyses showed an adequate power. In addition, genotype effects were neither found when different classification approaches were used nor when analyses were carried out in males or females only. The present findings suggest that the association of the 5-HTTLPR and FA seems to be a more labile phenomenon than previously assumed. Possible explanations and limitations are discussed.

White matter correlates of impaired attention control in major depressive disorder and healthy volunteers

BACKGROUND

Major depressive disorder (MDD) is associated with impaired attention control and alterations in frontal-subcortical connectivity. We hypothesized that attention control as assessed by Stroop task interference depends on white matter integrity in fronto-cingulate regions and assessed this relationship using diffusion tensor imaging (DTI) in MDD and healthy volunteers (HV).

METHODS

DTI images and Stroop task were acquired in 29 unmedicated MDD patients and 16 HVs, aged 18-65 years. The relationship between Stroop interference and fractional anisotropy (FA) was examined using region-of-interest (ROI) and tract-based spatial statistics (TBSS) analyses.

RESULTS

ROI analysis revealed that Stroop interference correlated positively with FA in left caudal anterior cingulate cortex (cACC) in HVs (r = 0.62, p = 0.01), but not in MDD (r = -0.05, p= 0.79) even after controlling for depression severity. The left cACC was among 4 ROIs in fronto-cingulate network where FA was lower in MDD relative to HVs (F_(1,41) = 8.87, p = 0.005). Additionally, TBSS showed the same group interaction of differences and correlations, although only at a statistical trend level.

LIMITATIONS

The modest sample size limits the generalizability of the findings.

CONCLUSIONS

Structural connectivity of white matter network of cACC correlated with magnitude of Stroop interference in HVs, but not MDD. The cACC-frontal network, sub-serving attention control, may be disrupted in MDD. Less cognitive control may include enhanced effects of salience in HVs, or less effective response inhibition in MDD. Further studies of salience and inhibition components of executive function may better elucidate the relationship between brain white matter changes and executive dysfunction in MDD.

Bad wrap: Myelin and myelin plasticity in health and disease

Human central nervous system myelin development extends well into the fourth decade of life, and this protracted period underscores the potential for experience to modulate myelination. The concept of myelin plasticity implies adaptability in myelin structure and function in response to experiences during development and beyond. Mounting evidence supports this concept of neuronal activity-regulated changes in myelin-forming cells, including oligodendrocyte precursor cell proliferation, oligodendrogenesis and modulation of myelin microstructure. In healthy individuals, myelin plasticity in associative white matter structures of the brain is implicated in learning and motor function in both rodents and humans. Activity-dependent changes in myelin-forming cells may influence the function of neural networks that depend on the convergence of numerous neural signals on both a temporal and spatial scale. However, dysregulation of myelin plasticity can disadvantageously alter myelin microstructure and result in aberrant circuit function or contribute to pathological cell proliferation. Emerging roles for myelin plasticity in normal neurological function and in disease are discussed. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 123-135, 2018.

Aberrant White Matter Microstructure in Children and Adolescents With the Subtype of Prader-Willi Syndrome at High Risk for Psychosis

Prader-Willi Syndrome (PWS) is a complex neurogenetic disorder caused by loss of the paternal 15q11.2-q13 locus, due to deletion (DEL), maternal uniparental disomy (mUPD), or imprinting center defects. Individuals with mUPD have up to 60% risk of developing psychosis in early adulthood. Given the increasing evidence for white matter abnormalities in psychotic disorders, we investigated white matter microstructure in children and adolescents with PWS, with a particular emphasis on the DEL and mUPD subtypes. Magnetic resonance diffusion weighted images were acquired in 35 directions at 3T and analyzed using fractional anisotropy (FA), mean, axial, and radial diffusivity (MD, AD, RD) values obtained by tract-based spatial statistics (TBSS) in 28 children and adolescents with PWS and 61 controls. In addition, we employed a recently developed white matter pothole approach, which does not require local FA differences to be spatially co-localized across subjects. After accounting for age and gender, individuals with PWS had significantly lower global FA and higher MD, compared with controls. Individuals with mUPD had lower FA in multiple regions including the corpus callosum, cingulate, and superior longitudinal fasciculus and larger potholes, compared with DEL and controls. The observed differences in individuals with mUPD are similar to the white matter abnormalities in individuals with psychotic disorders. Conversely, the subtle white matter abnormalities in individuals with DEL are consistent with their substantially lower risk of psychosis. Future studies to investigate the specific neurobiological mechanism underlying the differential psychosis risk between the DEL and mUPD subtypes of PWS are highly warranted.

Anxiety-related experience-dependent white matter structural differences in adolescence: A monozygotic twin difference approach

Anxiety is linked to deficits in structural and functional connectivity between limbic structures and pre-frontal cortices. We employed a monozygotic (MZ) twin difference design to examine the relationship between structural characteristics of the uncinate fasciculus (UF) measured by Diffusion Tensor Imaging (DTI) and anxiety symptoms in a sample of N = 100 monozygotic (genetically identical), adolescent twins. The MZ difference design allowed us focus on environmental factors that vary within twin pairs while controlling for genetic and environmental factors shared by twin pairs. Twins aged 13-18 years reported on symptoms of generalized anxiety and social phobia prior to participating in a neuroimaging visit. Regions of interest from the JHU ICBM atlas, including uncinate fasciculus and sagittal stratum as a control tract, were registered to the study template. We incorporated multiple diffusion tensor measures to characterize the white matter differences. Within twin pairs, the more anxious twin exhibited decreased fractional anisotropy (t = -2.22, p = 0.032) and axial diffusivity (t = -2.38, p = 0.022) in the left UF compared to the less anxious twin, controlling for age and gender. This study demonstrated the feasibility and advantages of adopting the MZ twin design for DTI measures in neuroimaging research.

Candidate Biomarkers in Children with Autism Spectrum Disorder: A Review of MRI Studies

Searching for effective biomarkers is one of the most challenging tasks in the research field of Autism Spectrum Disorder (ASD). Magnetic resonance imaging (MRI) provides a non-invasive and powerful tool for investigating changes in the structure, function, maturation, connectivity, and metabolism of the brain of children with ASD. Here, we review the more recent MRI studies in young children with ASD, aiming to provide candidate biomarkers for the diagnosis of childhood ASD. The review covers structural imaging methods, diffusion tensor imaging, resting-state functional MRI, and magnetic resonance spectroscopy. Future advances in neuroimaging techniques, as well as cross-disciplinary studies and large-scale collaborations will be needed for an integrated approach linking neuroimaging, genetics, and phenotypic data to allow the discovery of new, effective biomarkers.

A voxel-based diffusion tensor imaging study in unipolar and bipolar depression

OBJECTIVE

The absence of neurobiological diagnostic markers of bipolar disorder (BD) leads to its frequent misdiagnosis as unipolar depression (UD). We investigated if changes in fractional anisotropy (FA) could help to differentiate BD from UD in the state of depression.

METHODS

Using diffusion tensor imaging (DTI) we employed a voxel-based analysis approach to examine fractional anisotropy (FA) in 86 patients experiencing an acute major depressive episode according to DSM-IV (N=39 BD, mean age 39.2 years; N=43 UD, mean age 39.0 years), and 42 healthy controls (HC, mean age 36.1 years). The groups did not differ in sex, age or total education time. FA was investigated in white matter (FA >.2) and hypothesis-driven anatomically defined tracts (region-of-interest [ROI] analysis). Additionally, an exploratory gray matter FA analysis was performed.

RESULTS

White matter analysis showed decreased FA in the right corticospinal tract in UD vs HC and in the right corticospinal tract/superior longitudinal fascicle in BD vs HC and also in BD vs UD. ROI analysis revealed decreased FA in BD vs UD in the corpus callosum and in the cingulum. Gray matter exploratory analysis revealed decreased FA in the left middle frontal gyrus and in the right inferior frontal gyrus in UD vs HC, and in the left superior medial gyrus in BD vs HC.

CONCLUSION

This is one of very few studies directly showing differences in FA between BD and UD. Gray matter FA changes in prefrontal areas might be precursors for future prefrontal gray matter abnormalities in these disorders.

Altered microstructure of brain white matter in females with anorexia nervosa: a diffusion tensor imaging study

OBJECTIVE

Structural studies have reported anorexia nervosa (AN) patients with abnormal gray matter in several brain regions and dysfunction in some connected neural circuits. However, the role of white matter (WM) in AN patients has rarely been investigated. The present study aimed to assess alterations in WM microstructure of the entire brain in females with AN using a voxel-based method on diffusion tensor imaging (DTI) data.

MATERIALS AND METHODS

The study enrolled 8 female patients with AN and 14 age-matched females as controls (CW). The DTI data was collected from each subject to calculate the fractional anisotropy (FA) maps of the whole brain by the DTI-Studio software. Subsequently, a 2-sample t-test (P<0.05, corrected) was performed to detect the difference in FA maps of AN and CW group, and a Pearson's correlation analyzed the relationship between mean FA value of brain regions and body mass index (BMI).

RESULTS

Compared with CW, AN patients revealed a significant decrease in FA maps in the left superior frontal gyrus, medial frontal gyrus, anterior cingulate cortex, middle frontal gyrus, inferior frontal gyrus, thalamus, and bilateral insula. Moreover, significantly positive correlations were established between the mean FA value of the left inferior frontal gyrus, insula as well as thalamus and BMI in AN patients.

CONCLUSIONS

Our findings supported the presence of WM abnormality in patients with AN. The significant differences of FA maps, in patients with AN, were associated with their aberrant BMI. The results further improved our understanding of the pathophysiological mechanisms underlying AN.

Diffusion Capillary Phantom vs. Human Data: Outcomes for Reconstruction Methods Depend on Evaluation Medium

PURPOSE

Diffusion MRI provides a non-invasive way of estimating structural connectivity in the brain. Many studies have used diffusion phantoms as benchmarks to assess the performance of different tractography reconstruction algorithms and assumed that the results can be applied to in vivo studies. Here we examined whether quality metrics derived from a common, publically available, diffusion phantom can reliably predict tractography performance in human white matter tissue.

MATERIALS AND METHODS

We compared estimates of fiber length and fiber crossing among a simple tensor model (diffusion tensor imaging), a more complicated model (ball-and-sticks) and model-free (diffusion spectrum imaging, generalized q-sampling imaging) reconstruction methods using a capillary phantom and in vivo human data (N = 14).

RESULTS

Our analysis showed that evaluation outcomes differ depending on whether they were obtained from phantom or human data. Specifically, the diffusion phantom favored a more complicated model over a simple tensor model or model-free methods for resolving crossing fibers. On the other hand, the human studies showed the opposite pattern of results, with the model-free methods being more advantageous than model-based methods or simple tensor models. This performance difference was consistent across several metrics, including estimating fiber length and resolving fiber crossings in established white matter pathways.

CONCLUSIONS

These findings indicate that the construction of current capillary diffusion phantoms tends to favor complicated reconstruction models over a simple tensor model or model-free methods, whereas the in vivo data tends to produce opposite results. This brings into question the previous phantom-based evaluation approaches and suggests that a more realistic phantom or simulation is necessary to accurately predict the relative performance of different tractography reconstruction methods.

Age and Sex Effects on White Matter Tracts in Psychosis from Adolescence through Middle Adulthood

There is controversy regarding specificity of white matter abnormalities in psychosis, their deviation from healthy aging, and the influence of sex on these measures. We used diffusion tensor imaging to characterize putative white matter microstructure in 224 patients with psychosis and healthy volunteers across the age range of 15-64 years. Sixty-five younger (age <30 years; 47M/18F) patients with psychosis (all experiencing a first episode of illness) and 48 older (age ⩾30 years; 30M/18F) patients were age-matched to younger and older healthy volunteer groups (N=63 (40M/23F) and N=48 (29M/19F), respectively). The trajectories of two inter-hemispheric (splenium and genu), two projection (cortico-pontine and anterior thalamic), and five bilateral association (inferior fronto-occipital, inferior longitudinal, superior longitudinal, cingulum, and uncinate) tracts were quantified using tractography to derive measures of fractional anisotropy and mean, axial, and radial diffusivity. Fractional anisotropy was significantly lower in the inferior longitudinal fasciculus and superior longitudinal fasciculus in all patients compared with all healthy volunteers, with comparable effect sizes observed in both the younger and older patients compared with their respective healthy volunteer groups. Moreover, age-associated differences in fractional anisotropy within these tracts were comparable between groups across the age span. In addition, female patients had significantly lower fractional anisotropy across all tracts compared with female controls regardless of age. Our findings demonstrate comparable putative white matter abnormalities in two independent samples of patients with psychosis and argue against their progression in patients. These data further highlight the novel and potentially underappreciated role of sex in understanding white matter dysfunction in the neurobiology of psychosis.

Connectomics-based structural network alterations in obsessive-compulsive disorder

Given the strong involvement of affect in obsessive-compulsive disorder (OCD) and recent findings, the current cortico-striato-thalamo-cortical (CSTC) model of pathophysiology has repeatedly been questioned regarding the specific role of regions involved in emotion processing such as limbic areas. Employing a connectomics approach enables us to characterize structural connectivity on a whole-brain level, extending beyond the CSTC circuitry. Whole-brain structural networks of 41 patients and 42 matched healthy controls were analyzed based on 83 × 83 connectivity matrices derived from cortical and subcortical parcellation of structural T1-weighted magnetic resonance scans and deterministic fiber tracking based on diffusion tensor imaging data. To assess group differences in structural connectivity, the framework of network-based statistic (NBS) was applied. Graph theoretical measures were calculated to further assess local and global network characteristics. The NBS analysis revealed a single network consistently displaying decreased structural connectivity in patients comprising orbitofrontal, striatal, insula and temporo-limbic areas. In addition, graph theoretical measures indicated local alterations for amygdala and temporal pole while the overall topology of the network was preserved. To the best of our knowledge, this is the first study combining the NBS with graph theoretical measures in OCD. Along with regions commonly described in the CSTC model of pathophysiology, our results indicate an involvement of mainly temporo-limbic regions typically associated with emotion processing supporting their importance for neurobiological alterations in OCD.

Edge-Centered DTI Connectivity Analysis: Application to Schizophrenia

Diffusion tensor imaging (DTI) provides connectivity information that helps illuminate the processes underlying normal development as well as brain disorders such as autism and schizophrenia. Researchers have widely adopted graph representations to model DTI connectivity among brain structures; however, most measures of connectivity have been centered on nodes, rather than edges, in these graphs. We present an edge-based algorithm for assessing anatomic connectivity; this approach provides information about connections among brain structures, rather than information about structures themselves. This perspective allows us to formulate multivariate graph-based models of altered connectivity that distinguish among experimental groups. We demonstrate the utility of this approach by analyzing data from an ongoing study of schizophrenia.

Candidate gene networks and blood biomarkers of methamphetamine-associated psychosis: an integrative RNA-sequencing report

The clinical presentation, course and treatment of methamphetamine (METH)-associated psychosis (MAP) are similar to that observed in schizophrenia (SCZ) and subsequently MAP has been hypothesized as a pharmacological and environmental model of SCZ. However, several challenges currently exist in diagnosing MAP accurately at the molecular and neurocognitive level before the MAP model can contribute to the discovery of SCZ biomarkers. We directly assessed subcortical brain structural volumes and clinical parameters of MAP within the framework of an integrative genome-wide RNA-Seq blood transcriptome analysis of subjects diagnosed with MAP (N=10), METH dependency without psychosis (MA; N=10) and healthy controls (N=10). First, we identified discrete groups of co-expressed genes (that is, modules) and tested them for functional annotation and phenotypic relationships to brain structure volumes, life events and psychometric measurements. We discovered one MAP-associated module involved in ubiquitin-mediated proteolysis downregulation, enriched with 61 genes previously found implicated in psychosis and SCZ across independent blood and post-mortem brain studies using convergent functional genomic (CFG) evidence. This module demonstrated significant relationships with brain structure volumes including the anterior corpus callosum (CC) and the nucleus accumbens. Furthermore, a second MAP and psychoticism-associated module involved in circadian clock upregulation was also enriched with 39 CFG genes, further associated with the CC. Subsequently, a machine-learning analysis of differentially expressed genes identified single blood-based biomarkers able to differentiate controls from methamphetamine dependents with 87% accuracy and MAP from MA subjects with 95% accuracy. CFG evidence validated a significant proportion of these putative MAP biomarkers in independent studies including CLN3, FBP1, TBC1D2 and ZNF821 (RNA degradation), ELK3 and SINA3 (circadian clock) and PIGF and UHMK1 (ubiquitin-mediated proteolysis). Finally, focusing analysis on brain structure volumes revealed significantly lower bilateral hippocampal volumes in MAP subjects. Overall, these results suggest similar molecular and neurocognitive mechanisms underlying the pathophysiology of psychosis and SCZ regardless of substance abuse and provide preliminary evidence supporting the MAP paradigm as an exemplar for SCZ biomarker discovery.

Evidence for Accelerated Decline of Functional Brain Network Efficiency in Schizophrenia

Previous work suggests that individuals with schizophrenia display accelerated aging of white matter integrity, however, it is still unknown whether functional brain networks also decline at an elevated rate in schizophrenia. Given the known degradation of functional connectivity and the normal decline in cognitive functioning throughout healthy aging, we aimed to test the hypothesis that efficiency of large-scale functional brain networks supporting overall cognition, as well as integrity of hub nodes within those networks, show evidence of accelerated aging in schizophrenia. Using pseudo-resting state data in 54 healthy controls and 46 schizophrenia patients, in which task-dependent signal from 3 tasks was regressed out to approximate resting-state data, we observed a significant diagnosis by age interaction in the prediction of both global and local efficiency of the cingulo-opercular network, and of the local efficiency of the fronto-parietal network, but no interaction when predicting both default mode network and whole brain efficiency. We also observed a significant diagnosis by age interaction for the node degree of the right anterior insula, left dorsolateral prefrontal cortex, and dorsal anterior cingulate cortex. All interactions were driven by stronger negative associations between age and network metrics in the schizophrenia group than the healthy controls. These data provide evidence that is consistent with accelerated aging of large-scale functional brain networks in schizophrenia that support higher-order cognitive ability.

Dysfunctional decision-making related to white matter alterations in bipolar I disorder

OBJECTIVE

This study investigated how frontal white matter (WM) alterations in patients with bipolar I disorder (BD-I) are linked to motivational dysregulation, often reported in the form of risk-taking and impulsivity, and whether structure-function relations in patients might differ from healthy subjects (HC).

METHOD

We acquired diffusion data from 24 euthymic BD-I patients and 24 controls, to evaluate WM integrity of selected frontal tracts. Risk-taking was assessed by the Cambridge Gambling Task and impulsivity by self-report with the Barratt-Impulsiveness Scale.

RESULTS

BD-I patients displayed significantly lower integrity in the right cingulum compared to HC. They also showed more risk-taking behavior and reported increased trait-impulsivity. Risk-taking was negatively associated with WM integrity in the right cingulum. Impulsivity was not related to WM integrity in investigated tracts. Together with age and sex, FA in the cingulum explained 25% of variance in risk-taking scores in all study participants. The left inferior fronto-occipital fasciculus (IFOF) was specifically predictive of risk-taking behavior in BD-I patients, but not in HC.

LIMITATIONS

The employed parameters did not allow us to specify the exact origin of WM changes, nor did the method allow the analysis of specific brain subregions. Also, sample size was moderate and the sample included patients with lifetime alcohol dependence/abuse, hence effects found need replication and have to be interpreted with caution.

CONCLUSION

Our results further strengthen recent models linking structural changes in frontal networks to behavioral markers of BD-I. They extend recent findings by showing that risk-taking is also linked to the cingulum in BD-I and HC, while other prefrontal tracts (IFOF) are specifically implicated in risk-taking behavior in BD-I patients. Meanwhile, self-reported impulsivity was not associated with WM integrity of the tracts investigated in our study.

White matter alterations in anorexia nervosa: A systematic review of diffusion tensor imaging studies

AIM

To identify findings concerning white matter (WM) fibre microstructural alterations in anorexia nervosa (AN).

METHODS

A systematic electronic search was undertaken in several databases up to April 2015. The search strategy aimed to locate all studies published in English or Spanish that included participants with AN and which investigated WM using diffusion tensor imaging (DTI). Trials were assessed for quality assessment according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses checklist and a published quality index guideline.

RESULTS

A total of 6 studies met the inclusion criteria, four of people in the acute state of the illness, one included both recovered and unwell participants, and one included people who had recovered. Participants were female with ages ranging from 14 to 29 years. All studies but one measured a range of psychopathological features. Fractional anisotropy and mean diffusivity were the main DTI correlates reported. Alterations were reported in a range of WM structures of the limbic system, most often of the fornix and cingulum as well as the fronto-occipital fibre tracts, i.e., regions associated with anxiety, body image and cognitive function. Subtle abnormalities also appeared to persist after recovery.

CONCLUSION

This diversity likely reflects the symptom complexity of AN. However, there were few studies, they applied different methodologies, and all were cross-sectional.

Serum S100B Protein is Specifically Related to White Matter Changes in Schizophrenia

Background: Schizophrenia can be conceptualized as a form of dysconnectivity between brain regions.To investigate the neurobiological foundation of dysconnectivity, one approach is to analyze white matter structures, such as the pathology of fiber tracks. S100B is considered a marker protein for glial cells, in particular oligodendrocytes and astroglia, that passes the blood brain barrier and is detectable in peripheral blood. Earlier Studies have consistently reported increased S100B levels in schizophrenia. In this study, we aim to investigate associations between S100B and structural white matter abnormalities.

Methods: We analyzed data of 17 unmedicated schizophrenic patients (first and recurrent episode) and 22 controls. We used voxel based morphometry (VBM) to detect group differences of white matter structures as obtained from T1-weighted MR-images and considered S100B serum levels as a regressor in an age-corrected interaction analysis.

Results: S100B was increased in both patient subgroups. Using VBM, we found clusters indicating significant differences of the association between S100B concentration and white matter. Involved anatomical structures are the posterior cingulate bundle and temporal white matter structures assigned to the superior longitudinal fasciculus.

Conclusions: S100B-associated alterations of white matter are shown to be existent already at time of first manifestation of psychosis and are distinct from findings in recurrent episode patients. This suggests involvement of S100B in an ongoing and dynamic process associated with structural brain changes in schizophrenia. However, it remains elusive whether increased S100B serum concentrations in psychotic patients represent a protective response to a continuous pathogenic process or if elevated S100B levels are actively involved in promoting structural brain damage.

White matter microstructure and impulsivity in methamphetamine dependence with and without a history of psychosis

BACKGROUND

Methamphetamine (MA) use may lead to white matter injury and to a range of behavioral problems and psychiatric disorders, including psychosis. The present study sought to assess white matter microstructural impairment as well as impulsive behavior in MA dependence and MA-associated psychosis (MAP).

METHODS

Thirty patients with a history of MAP, 39 participants with MA dependence and 40 healthy controls underwent diffusion tensor imaging (DTI). Participants also completed the UPPS-P impulsive behavior questionnaire. We applied tract-based spatial statistics (TBSS) to investigate group differences in mean diffusivity (MD), fractional anisotropy (FA), axial (λ‖ ) and radial diffusivity (λ⊥ ), and their association with impulsivity scores and psychotic symptoms.

RESULTS

The MAP group displayed widespread higher MD, λ‖ and λ⊥ levels compared to both controls and the MA group, and lower FA in extensive white matter areas relative to controls. MD levels correlated positively with negative psychotic symptoms in MAP. No significant DTI group differences were found between the MA group and controls. Both clinical groups showed high levels of impulsivity, and this dysfunction was associated with DTI measures in frontal white matter tracts.

CONCLUSIONS

MAP patients show distinct patterns of impaired white matter integrity of global nature relative to controls and the MA group. Future work to investigate the precise nature and timing of alterations in MAP is needed. The results are further suggestive of frontal white matter pathology playing a role in impulsivity in MA dependence and MAP. Hum Brain Mapp 37:2055-2067, 2016. © 2016 Wiley Periodicals, Inc.

Imaging the "At-Risk" Brain: Future Directions

OBJECTIVES

Clinical neuroscience is increasingly turning to imaging the human brain for answers to a range of questions and challenges. To date, the majority of studies have focused on the neural basis of current psychiatric symptoms, which can facilitate the identification of neurobiological markers for diagnosis. However, the increasing availability and feasibility of using imaging modalities, such as diffusion imaging and resting-state fMRI, enable longitudinal mapping of brain development. This shift in the field is opening the possibility of identifying predictive markers of risk or prognosis, and also represents a critical missing element for efforts to promote personalized or individualized medicine in psychiatry (i.e., stratified psychiatry).

METHODS

The present work provides a selective review of potentially high-yield populations for longitudinal examination with MRI, based upon our understanding of risk from epidemiologic studies and initial MRI findings.

RESULTS

Our discussion is organized into three topic areas: (1) practical considerations for establishing temporal precedence in psychiatric research; (2) readiness of the field for conducting longitudinal MRI, particularly for neurodevelopmental questions; and (3) illustrations of high-yield populations and time windows for examination that can be used to rapidly generate meaningful and useful data. Particular emphasis is placed on the implementation of time-appropriate, developmentally informed longitudinal designs, capable of facilitating the identification of biomarkers predictive of risk and prognosis.

CONCLUSIONS

Strategic longitudinal examination of the brain at-risk has the potential to bring the concepts of early intervention and prevention to psychiatry.

Comparison of 3D orientation distribution functions measured with confocal microscopy and diffusion MRI

The ability of diffusion MRI (dMRI) fiber tractography to non-invasively map three-dimensional (3D) anatomical networks in the human brain has made it a valuable tool in both clinical and research settings. However, there are many assumptions inherent to any tractography algorithm that can limit the accuracy of the reconstructed fiber tracts. Among them is the assumption that the diffusion-weighted images accurately reflect the underlying fiber orientation distribution (FOD) in the MRI voxel. Consequently, validating dMRI's ability to assess the underlying fiber orientation in each voxel is critical for its use as a biomedical tool. Here, using post-mortem histology and confocal microscopy, we present a method to perform histological validation of orientation functions in 3D, which has previously been limited to two-dimensional analysis of tissue sections. We demonstrate the ability to extract the 3D FOD from confocal z-stacks, and quantify the agreement between the MRI estimates of orientation information obtained using constrained spherical deconvolution (CSD) and the true geometry of the fibers. We find an orientation error of approximately 6° in voxels containing nearly parallel fibers, and 10-11° in crossing fiber regions, and note that CSD was unable to resolve fibers crossing at angles below 60° in our dataset. This is the first time that the 3D white matter orientation distribution is calculated from histology and compared to dMRI. Thus, this technique serves as a gold standard for dMRI validation studies - providing the ability to determine the extent to which the dMRI signal is consistent with the histological FOD, and to establish how well different dMRI models can predict the ground truth FOD.

Molecular substrates of schizophrenia: homeostatic signaling to connectivity

Schizophrenia (SZ) is a devastating psychiatric condition affecting numerous brain systems. Recent studies have identified genetic factors that confer an increased risk of SZ and participate in the disease etiopathogenesis. In parallel to such bottom-up approaches, other studies have extensively reported biological changes in patients by brain imaging, neurochemical and pharmacological approaches. This review highlights the molecular substrates identified through studies with SZ patients, namely those using top-down approaches, while also referring to the fruitful outcomes of recent genetic studies. We have subclassified the molecular substrates by system, focusing on elements of neurotransmission, targets in white matter-associated connectivity, immune/inflammatory and oxidative stress-related substrates, and molecules in endocrine and metabolic cascades. We further touch on cross-talk among these systems and comment on the utility of animal models in charting the developmental progression and interaction of these substrates. Based on this comprehensive information, we propose a framework for SZ research based on the hypothesis of an imbalance in homeostatic signaling from immune/inflammatory, oxidative stress, endocrine and metabolic cascades that, at least in part, underlies deficits in neural connectivity relevant to SZ. Thus, this review aims to provide information that is translationally useful and complementary to pathogenic hypotheses that have emerged from genetic studies. Based on such advances in SZ research, it is highly expected that we will discover biomarkers that may help in the early intervention, diagnosis or treatment of SZ.

Anterior cingulate cortex-related connectivity in first-episode schizophrenia: a spectral dynamic causal modeling study with functional magnetic resonance imaging

Understanding the neural basis of schizophrenia (SZ) is important for shedding light on the neurobiological mechanisms underlying this mental disorder. Structural and functional alterations in the anterior cingulate cortex (ACC), dorsolateral prefrontal cortex (DLPFC), hippocampus, and medial prefrontal cortex (MPFC) have been implicated in the neurobiology of SZ. However, the effective connectivity among them in SZ remains unclear. The current study investigated how neuronal pathways involving these regions were affected in first-episode SZ using functional magnetic resonance imaging (fMRI). Forty-nine patients with a first-episode of psychosis and diagnosis of SZ-according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision-were studied. Fifty healthy controls (HCs) were included for comparison. All subjects underwent resting state fMRI. We used spectral dynamic causal modeling (DCM) to estimate directed connections among the bilateral ACC, DLPFC, hippocampus, and MPFC. We characterized the differences using Bayesian parameter averaging (BPA) in addition to classical inference (t-test). In addition to common effective connectivity in these two groups, HCs displayed widespread significant connections predominantly involved in ACC not detected in SZ patients, but SZ showed few connections. Based on BPA results, SZ patients exhibited anterior cingulate cortico-prefrontal-hippocampal hyperconnectivity, as well as ACC-related and hippocampal-dorsolateral prefrontal-medial prefrontal hypoconnectivity. In summary, spectral DCM revealed the pattern of effective connectivity involving ACC in patients with first-episode SZ. This study provides a potential link between SZ and dysfunction of ACC, creating an ideal situation to associate mechanisms behind SZ with aberrant connectivity among these cognition and emotion-related regions.

Glutathione Deficit Affects the Integrity and Function of the Fimbria/Fornix and Anterior Commissure in Mice: Relevance for Schizophrenia

BACKGROUND

Structural anomalies of white matter are found in various brain regions of patients with schizophrenia and bipolar and other psychiatric disorders, but the causes at the cellular and molecular levels remain unclear. Oxidative stress and redox dysregulation have been proposed to play a role in the pathophysiology of several psychiatric conditions, but their anatomical and functional consequences are poorly understood. The aim of this study was to investigate white matter throughout the brain in a preclinical model of redox dysregulation.

METHODS

In a mouse model with impaired glutathione synthesis (Gclm KO), a state-of-the-art multimodal magnetic resonance protocol at high field (14.1 T) was used to assess longitudinally the white matter structure, prefrontal neurochemical profile, and ventricular volume. Electrophysiological recordings in the abnormal white matter tracts identified by diffusion tensor imaging were performed to characterize the functional consequences of fractional anisotropy alterations.

RESULTS

Structural alterations observed at peri-pubertal age and adulthood in Gclm KO mice were restricted to the anterior commissure and fornix-fimbria. Reduced fractional anisotropy in the anterior commissure (-7.5% ± 1.9, P<.01) and fornix-fimbria (-4.5% ± 1.3, P<.05) were accompanied by reduced conduction velocity in fast-conducting fibers of the posterior limb of the anterior commissure (-14.3% ± 5.1, P<.05) and slow-conducting fibers of the fornix-fimbria (-8.6% ± 2.6, P<.05). Ventricular enlargement was found at peri-puberty (+25% ± 8 P<.05) but not in adult Gclm KO mice.

CONCLUSIONS

Glutathione deficit in Gclm KO mice affects ventricular size and the integrity of the fornix-fimbria and anterior commissure. This suggests that redox dysregulation could contribute during neurodevelopment to the impaired white matter and ventricle enlargement observed in schizophrenia and other psychiatric disorders.

Interpersonal traits of psychopathy linked to reduced integrity of the uncinate fasciculus

Psychopathy is a personality disorder characterized by callous lack of empathy, impulsive antisocial behavior, and criminal recidivism. Here, we performed the largest diffusion tensor imaging (DTI) study of incarcerated criminal offenders to date (N = 147) to determine whether psychopathy severity is linked to the microstructural integrity of major white matter tracts in the brain. Consistent with the results of previous studies in smaller samples, we found that psychopathy was associated with reduced fractional anisotropy in the right uncinate fasciculus (UF; the major white matter tract connecting ventral frontal and anterior temporal cortices). We found no such association in the left UF or in adjacent frontal or temporal white matter tracts. Moreover, the right UF finding was specifically related to the interpersonal features of psychopathy (glib superficial charm, grandiose sense of self-worth, pathological lying, manipulativeness), rather than the affective, antisocial, or lifestyle features. These results indicate a neural marker for this key dimension of psychopathic symptomatology.