Detecting microstructural white matter abnormalities of frontal pathways in children with ADHD using advanced diffusion models

Facial expression recognition ability and its neuropsychological mechanisms in children with attention deficit and hyperactive disorder

Attention deficit and hyperactive disorder (ADHD) is a chronic neurodevelopmental disorder characterized by inattention, hyperactivity-impulsivity, and working memory deficits. Social dysfunction is one of the major challenges faced by children with ADHD. It has been found that children with ADHD can't perform as well as typically developing children on facial expression recognition (FER) tasks. Generally, children with ADHD have some difficulties in FER, while some studies suggest that they have no significant differences in accuracy of specific emotion recognition compared with typically developing children. The neuropsychological mechanisms underlying these difficulties are as follows. First, neuroanatomically. Compared to typically developing children, children with ADHD show smaller gray matter volume and surface area in the amygdala and medial prefrontal cortex regions, as well as reduced density and volume of axons/cells in certain frontal white matter fiber tracts. Second, neurophysiologically. Children with ADHD exhibit increased slow-wave activity in their electroencephalogram, and event-related potential studies reveal abnormalities in emotional regulation and responses to angry faces when facing facial stimuli. Third, psychologically. Psychosocial stressors may influence FER abilities in children with ADHD, and sleep deprivation in ADHD children may significantly increase their recognition threshold for negative expressions such as sadness and anger. This article reviews research progress over the past three years on FER abilities of children with ADHD, analyzing the FER deficit in children with ADHD from three dimensions: neuroanatomy, neurophysiology and psychology, aiming to provide new perspectives for further research and clinical treatment of ADHD.

Is the deficit in attention-deficit/hyperactivity disorder a concentration deficit?

Attention-deficit/hyperactivity disorder (ADHD) is comprised of two behavioral clusters of symptoms, inattention and hyperactivity/impulsivity. Numerous studies have attempted to address the underlying neuropsychological mechanism of ADHD. However, there is still no uniform mechanism that can fully explain both inattention and hyperactivity/impulsivity symptoms. This review describes the research findings that have shifted the focus from cognitive selective attention to executive function deficits and notes that the prominence of the attention deficit remains unclear. As ADHD is not consistently explained by cognitive selective attention but rather with cognitive sustained attention/vigilance and executive function deficits, this review suggests that concentration deficit is likely the cause of inattention symptoms. Indeed, considering concentration deficit as the cause of inattention symptoms may better describe the underlying difficulties of maintaining and controlling attention in ADHD. In addition, as concentration, impulsivity, and hyperactivity may share a common cognitive deficit, this shift in focus may help in identifying a single mechanism for all ADHD symptoms.

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.

Sex differences in atypical fronto-subcortical structural connectivity among children with attention-deficit/hyperactivity disorder: Associations with delay discounting

PURPOSE

Atypical fronto-subcortical neural circuitry has been implicated in the pathophysiology of attention-deficit/hyperactivity disorder (ADHD), including connections between prefrontal cortical regions involved in top-down cognitive control and subcortical limbic structures (striatum and amygdala) involved in bottom-up reward and emotional processing. The integrity of fronto-subcortical connections may also relate to interindividual variability in delay discounting, or a preference for smaller, immediate over larger, delayed rewards, which is associated with ADHD, with recent evidence of ADHD-related sex differences.

METHODS

We applied diffusion tensor imaging to compare the integrity of the white matter connections within fronto-subcortical tracts among 187 8-12 year-old children either with ADHD ((n = 106; 29 girls) or typically developing (TD) controls ((n = 81; 28 girls). Analyses focused on diagnostic group differences in fractional anisotropy (FA) within fronto-subcortical circuitry implicated in delay discounting, connecting subregions of the striatum (dorsal executive and ventral limbic areas) and amygdala with prefrontal regions of interest (dorsolateral [dlPFC], orbitofrontal [OFC] and anterior cingulate cortex [ACC]), and associations with two behavioral assessments of delay discounting.

RESULTS

Children with ADHD showed reduced FA in tracts connecting OFC with ventral striatum, regardless of sex, whereas reduced FA in the OFC-amygdala and ventral ACC-amygdala tracts were specific to boys with ADHD. Across diagnostic groups and sex, reduced FA in the dorsal ACC-executive striatum tract correlated with greater game time delay discounting.

CONCLUSIONS

These results suggest a potential neurobiological substrate of heightened delay discounting in children with ADHD and support the need for additional studies including larger sample sizes of girls with ADHD to further elucidate ADHD-related sex differences in these relationships.

Neurite orientation dispersion and density imaging of white matter microstructure in sensory processing dysfunction with versus without comorbid ADHD

Introduction

Sensory Processing Dysfunction (SPD) is common yet understudied, affecting up to one in six children with 40% experiencing co-occurring challenges with attention. The neural architecture of SPD with Attention Deficit and Hyperactivity Disorder (ADHD) (SPD+ADHD) versus SPD without ADHD (SPD-ADHD) has yet to be explored in diffusion tensor imaging (DTI) and Neurite Orientation Dispersion and Density Imaging (NODDI) has yet to be examined.

Methods

The present study computed DTI and NODDI biophysical model parameter maps of one hundred children with SPD. Global, regional and voxel-level white matter tract measures were analyzed and compared between SPD+ADHD and SPD-ADHD groups.

Results

SPD+ADHD children had global WM Fractional Anisotropy (FA) and Neurite Density Index (NDI) that trended lower than SPD-ADHD children, primarily in boys only. Data-driven voxelwise and WM tract-based analysis revealed statistically significant decreases of NDI in boys with SPD+ADHD compared to those with SPD-ADHD, primarily in projection tracts of the internal capsule and commissural fibers of the splenium of the corpus callosum.

Conclusion

We conclude that WM microstructure is more delayed/disrupted in boys with SPD+ADHD compared to SPD-ADHD, with NODDI showing a larger effect than DTI. This may represent the combined WM pathology of SPD and ADHD, or it may result from a greater degree of SPD WM pathology causing the development of ADHD.

A preliminary study of white matter correlates of a laboratory measure of attention and motor stability in attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a complex behavioral disorder, often difficult and time consuming to diagnose. Laboratory assessment of ADHD-related constructs of attention and motor activity may be helpful in elucidating neurobiology; however, neuroimaging studies evaluating laboratory measures of ADHD are lacking. In this preliminary study, we assessed the association between fractional anisotropy (FA), a measure of white matter microstructure, and laboratory measures of attention and motor behavior using the QbTest, a widely used measure thought to improve clinician diagnostic confidence. This is the first look at neural correlates of this widely used measure. The sample included adolescents and young adults (ages 12-20, 35% female) with ADHD (n = 31) and without (n = 52). As expected, ADHD status was associated with motor activity, and cognitive inattention and impulsivity in the laboratory. With regard to MRI findings, laboratory observed motor activity and inattention were associated with greater FA in white matter regions of the primary motor cortex. All three laboratory observations were associated with lower FA in regions subserving fronto-striatal-thalamic and frontoparietal (i.e. superior longitudinal fasciculus) circuitry. Further, FA in white matter regions of the prefrontal cortex appeared to mediate the relationship between ADHD status and motor activity on the QbTest. These findings, while preliminary, suggest that performance on certain laboratory tasks is informative with regard to neurobiological correlates of subdomains of the complex ADHD phenotype. In particular, we provide novel evidence for a relationship between an objective measure of motor hyperactivity and white matter microstructure in motor and attentional networks.

Prenatal Stress Induces Translational Disruption Associated with Myelination Deficits

Disruptions to neurodevelopment are known to be linked to behavioral disorders in childhood and into adulthood. The fetal brain is extremely vulnerable to stimuli that alter inhibitory GABAergic pathways and critical myelination processes, programing long-term neurobehavioral disruption. The maturation of the GABAergic system into the major inhibitory pathway in the brain and the development of oligodendrocytes into mature cells capable of producing myelin are integral components of optimal neurodevelopment. The current study aimed to elucidate prenatal stress-induced mechanisms that disrupt these processes and to delineate the role of placental pathways in these adverse outcomes. Pregnant guinea pig dams were exposed to prenatal stress with strobe light exposure for 2 h/day on gestational age (GA) 35, 40, 45, 50, 55, 60, and 65, and groups of fetuses and placentae were collected after the stress exposure on GA40, GA50, GA60, and GA69 (term). Fetal plasma, placental, and brain tissue were collected for allopregnanolone and cortisol quantification with ELISA. Relative mRNA expression of genes of specific pathways of interest was examined with real-time PCR in placental and hippocampal tissue, and myelin basic protein (MBP) was quantified immunohistochemically in the hippocampus and surrounding regions for assessment of mature myelin. Prenatal stress in mid-late gestation resulted in disruptions to the translational machinery responsible for the production of myelin and decreased myelin coverage in the hippocampus and surrounding regions. The male placenta showed an initial protective increase in allopregnanolone concentrations in response to maternal psychosocial stress. The male and female placentae had a sex-dependent increase in neurosteroidogenic enzymes at term following prenatal stress. Independent from exposure to prenatal stress, at gestational day 60 - a critical period for myelin development, the placentae of female fetuses had increased capability of preventing cortisol transfer to the fetus through expression of 11-beta-hydroxysteroid dehydrogenase types 1 and 2. The deficits early in the process of maturation of myelination indicate that the reduced myelination observed at childhood equivalence in previous studies begins in fetal life. This negative programing persists into childhood, potentially due to dysregulation of MBP translation processes. Expression patterns of neurosteroidogenic enzymes in the placenta at term following stress may identify at-risk fetuses that have been exposed to a stressful in utero environment.

Spatially regularized low-rank tensor approximation for accurate and fast tractography

Tractography based on diffusion Magnetic Resonance Imaging (dMRI) is the prevalent approach to the in vivo delineation of white matter tracts in the human brain. Many tractography methods rely on models of multiple fiber compartments, but the local dMRI information is not always sufficient to reliably estimate the directions of secondary fibers. Therefore, we introduce two novel approaches that use spatial regularization to make multi-fiber tractography more stable. Both represent the fiber Orientation Distribution Function (fODF) as a symmetric fourth-order tensor, and recover multiple fiber orientations via low-rank approximation. Our first approach computes a joint approximation over suitably weighted local neighborhoods with an efficient alternating optimization. The second approach integrates the low-rank approximation into a current state-of-the-art tractography algorithm based on the unscented Kalman filter (UKF). These methods were applied in three different scenarios. First, we demonstrate that they improve tractography even in high-quality data from the Human Connectome Project, and that they maintain useful results with a small fraction of the measurements. Second, on the 2015 ISMRM tractography challenge, they increase overlap, while reducing overreach, compared to low-rank approximation without joint optimization or the traditional UKF, respectively. Finally, our methods permit a more comprehensive reconstruction of tracts surrounding a tumor in a clinical dataset. Overall, both approaches improve reconstruction quality. At the same time, our modified UKF significantly reduces the computational effort compared to its traditional counterpart, and to our joint approximation. However, when used with ROI-based seeding, joint approximation more fully recovers fiber spread.

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.

Population level multimodal neuroimaging correlates of attention-deficit hyperactivity disorder among children

Objectives

Leveraging a large population-level morphologic, microstructural, and functional neuroimaging dataset, we aimed to elucidate the underlying neurobiology of attention-deficit hyperactivity disorder (ADHD) in children. In addition, we evaluated the applicability of machine learning classifiers to predict ADHD diagnosis based on imaging and clinical information.

Methods

From the Adolescents Behavior Cognitive Development (ABCD) database, we included 1,798 children with ADHD diagnosis and 6,007 without ADHD. In multivariate logistic regression adjusted for age and sex, we examined the association of ADHD with different neuroimaging metrics. The neuroimaging metrics included fractional anisotropy (FA), neurite density (ND), mean-(MD), radial-(RD), and axial diffusivity (AD) of white matter (WM) tracts, cortical region thickness and surface areas from T1-MPRAGE series, and functional network connectivity correlations from resting-state fMRI.

Results

Children with ADHD showed markers of pervasive reduced microstructural integrity in white matter (WM) with diminished neural density and fiber-tracks volumes - most notable in the frontal and parietal lobes. In addition, ADHD diagnosis was associated with reduced cortical volume and surface area, especially in the temporal and frontal regions. In functional MRI studies, ADHD children had reduced connectivity among default-mode network and the central and dorsal attention networks, which are implicated in concentration and attention function. The best performing combination of feature selection and machine learning classifier could achieve a receiver operating characteristics area under curve of 0.613 (95% confidence interval = 0.580-0.645) to predict ADHD diagnosis in independent validation, using a combination of multimodal imaging metrics and clinical variables.

Conclusion

Our study highlights the neurobiological implication of frontal lobe cortex and associate WM tracts in pathogenesis of childhood ADHD. We also demonstrated possible potentials and limitations of machine learning models to assist with ADHD diagnosis in a general population cohort based on multimodal neuroimaging metrics.

Investigating the contribution of cytoarchitecture to diffusion MRI measures in gray matter using histology

Postmortem studies are currently considered a gold standard for investigating brain structure at the cellular level. To investigate cellular changes in the context of human development, aging, or disease treatment, non-invasive in-vivo imaging methods such as diffusion MRI (dMRI) are needed. However, dMRI measures are only indirect measures and require validation in gray matter (GM) in the context of their sensitivity to the underlying cytoarchitecture, which has been lacking. Therefore, in this study we conducted direct comparisons between in-vivo dMRI measures and histology acquired from the same four rhesus monkeys. Average and heterogeneity of fractional anisotropy and trace from diffusion tensor imaging and mean squared displacement (MSD) and return-to-origin-probability from biexponential model were calculated in nine cytoarchitectonically different GM regions using dMRI data. DMRI measures were compared with corresponding histology measures of regional average and heterogeneity in cell area density. Results show that both average and heterogeneity in trace and MSD measures are sensitive to the underlying cytoarchitecture (cell area density) and capture different aspects of cell composition and organization. Trace and MSD thus would prove valuable as non-invasive imaging biomarkers in future studies investigating GM cytoarchitectural changes related to development and aging as well as abnormal cellular pathologies in clinical studies.

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.

Frontal interhemispheric structural connectivity, attention, and executive function in children with perinatal stroke

Perinatal stroke affects ∼1 in 1000 births and concomitant cognitive impairments are common but poorly understood. Rates of Attention Deficit/Hyperactivity Disorder (ADHD) are increased 5-10× and executive dysfunction can be disabling. We used diffusion imaging to investigate whether stroke-related differences in frontal white matter (WM) relate to cognitive impairments. Anterior forceps were isolated using tractography and sampled along the tract. Resulting metrics quantified frontal WM microstructure. Associations between WM metrics and parent ratings of ADHD symptoms (ADHD-5 rating scale) and executive functioning (Behavior Rating Inventory of Executive Function (BRIEF)) were explored. Eighty-three children were recruited (arterial ischemic stroke [AIS] n = 26; periventricular venous infarction [PVI] n = 26; controls n = 31). WM metrics were altered for stroke groups compared to controls. Along-tract analyses showed differences in WM metrics in areas approximating the lesion as well as more remote differences at midline and in the nonlesioned hemisphere. WM metrics correlated with parental ratings of ADHD and executive function such that higher diffusivity values were associated with poorer function. These findings suggest that underlying microstructure of frontal white matter quantified via tractography may provide a relevant biomarker associated with cognition and behavior in children with perinatal stroke.

Individual differences in white matter of the uncinate fasciculus and inferior fronto-occipital fasciculus: possible early biomarkers for callous-unemotional behaviors in young children with disruptive behavior problems

BACKGROUND

Callous-unemotional (CU) behaviors are important for identifying severe patterns of conduct problems (CP). One major fiber tract implicated in the development of CP is the uncinate fasciculus (UF), which connects amygdala and orbitofrontal cortex (OFC). The goals of the current study were to (a) explore differences in the white matter microstructure in the UF and other major fiber tracks between young typically developing (TD) children and those with a disruptive behavior disorder (DBD) and (b) explore, within the DBD group, whether individual differences in these white matter tracts relate to co-occurring CP and CU behaviors.

METHODS

Participants included 198 young children (69% boys, M_age  = 5.66 years; 80% Latinx; 48.5% TD). CU behaviors and CP were measured via a combination of teacher/parent ratings. Non-invasive diffusion-weighted imaging (DWI) was used to measure fractional anisotropy (FA), an indirect indicator of white matter properties.

RESULTS

Relative to TD children, children in the DBD group had reduced FA on four out of the five fiber tracks we examined (except for cingulum and right ILF), even after accounting for whole brain FA, sex, movement, parental income, and IQ. Within the DBD group, no associations were found between CP and reduced white matter integrity across any of the fiber tracks examined. However, we found that even after accounting for CP, ADHD symptomology, and a host of covariates (whole brain FA, sex, movement, parental income, and IQ), CU behaviors were independently related to reduced FA in bilateral UF and left inferior fronto-occipital fasciculus (IFOF) in the DBD group, but this was not the case for TD children.

CONCLUSIONS

Alterations in the white matter microstructure within bilateral UF and left IFOF may be biomarkers of CU behaviors, even in very young children.

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.

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.

Chronic Administrations of Guanfacine on Mesocortical Catecholaminergic and Thalamocortical Glutamatergic Transmissions

It has been established that the selective α2A adrenoceptor agonist guanfacine reduces hyperactivity and improves cognitive impairment in patients with attention-deficit/hyperactivity disorder (ADHD). The major mechanisms of guanfacine are considered to involve the activation of the postsynaptic α2A adrenoceptor of glutamatergic pyramidal neurons in the frontal cortex, but the effects of chronic guanfacine administration on catecholaminergic and glutamatergic transmissions associated with the orbitofrontal cortex (OFC) are yet to be clarified. The actions of guanfacine on catecholaminergic transmission, the effects of acutely local and systemically chronic (for 7 days) administrations of guanfacine on catecholamine release in pathways from the locus coeruleus (LC) to OFC, the ventral tegmental area (VTA) and reticular thalamic-nucleus (RTN), from VTA to OFC, from RTN to the mediodorsal thalamic-nucleus (MDTN), and from MDTN to OFC were determined using multi-probe microdialysis with ultra-high performance liquid chromatography. Additionally, the effects of chronic guanfacine administration on the expression of the α2A adrenoceptor in the plasma membrane fraction of OFC, VTA and LC were examined using a capillary immunoblotting system. The acute local administration of therapeutically relevant concentrations of guanfacine into the LC decreased norepinephrine release in the OFC, VTA and RTN without affecting dopamine release in the OFC. Systemically, chronic administration of therapeutically relevant doses of guanfacine for 14 days increased the basal release of norepinephrine in the OFC, VTA, RTN, and dopamine release in the OFC via the downregulation of the α2A adrenoceptor in the LC, OFC and VTA. Furthermore, systemically, chronic guanfacine administration did not affect intrathalamic GABAergic transmission, but it phasically enhanced thalamocortical glutamatergic transmission. The present study demonstrated the dual actions of guanfacine on catecholaminergic transmission-acute attenuation of noradrenergic transmission and chronic enhancement of noradrenergic transmission and thalamocortical glutamatergic transmission. These dual actions of guanfacine probably contribute to the clinical effects of guanfacine against ADHD.

Animal models of attention-deficit hyperactivity disorder (ADHD)

Attention-deficit hyperactivity disorder (ADHD) is a heterogeneous neuropsychiatric disorder characterized by three primary symptoms hyperactivity, attention deficit, and impulsiveness, observed in both children and adults. In childhood, this disorder is more common in boys than in girls, and at least 75% will continue to suffer from the disorder until adulthood. Individuals with ADHD generally have poor academic, occupational, and social functioning resulting from developmentally inappropriate levels of hyperactivity and impulsivity, as well as impaired ability to maintain attention on motivationally relevant tasks. Very few drugs available in clinical practice altogether abolish the symptoms of ADHD, therefore, to find new drugs and target it is essential to understand the neuropathological, neurochemical, and genetic alterations that lead to the progression of ADHD. With this contrast, an animal study is the best approach because animal models provide relatively fast invasive manipulation, rigorous hypothesis testing, as well as it provides a better angle to understand the pathological mechanisms involved in disease progression. Moreover, animal models, especially for ADHD, serve with good predictive validity would allow the assessment and development of new therapeutic interventions, with this aim, the present review collect the various animal models on a single platform so that the research can select an appropriate model to pursue his study.

Increased Brain Iron Detection by Voxel-Based Quantitative Susceptibility Mapping in Type 2 Diabetes Mellitus Patients With an Executive Function Decline

Purpose

Brain iron accumulation has been suggested as a pathomechanism in patients with type 2 diabetes mellitus (T2DM) with cognitive impairment. This research aims to examine the total-brain pattern of iron accumulation in relation to executive function decline in patients with T2DM by voxel-based quantitative susceptibility mapping (QSM) analysis.

Materials and Methods

A total of 32 patients with T2DM and 34 age- and sex-matched healthy controls (HCs) were enrolled in this study. All participants underwent brain magnetic resonance examination, and 48 individuals underwent cognitive function assessments. Imaging data were collected with three-dimensional fast low-angle shot sequences to achieve magnitude as well as phase images. Using voxel-based QSM analysis, we compared the voxel-wise susceptibility values of the whole brain among groups and explored whether the susceptibility values had correlations with cognitive data.

Results

Among the 66 participants, cognitive function was estimated in 23 patients with T2DM (11 males and 12 females; average age, 64.65 ± 8.44 years) and 25 HCs (13 males and 12 females; average age, 61.20 ± 7.62 years). T2DM patients exhibited significantly (t = 4.288, P < 0.001) lower Montreal Cognitive Assessment (MoCA) scores [T2DM, 27 (27, 28); HCs, 29 (28, 29); normal standard ≥ 26)] and higher Trail-making Test (TMT)-A/TMT-B scores [71 (51, 100)/185 (149, 260)] than HCs [53 (36.5, 63.5)/150 (103, 172.5)] (Z = 2.612, P = 0.009; Z = 2.797, P = 0.005). Subjects with T2DM showed significantly higher susceptibility values than HCs in the caudate/putamen/pallidum, frontal inferior triangular gyrus, and precentral gyrus on the right hemisphere. In contrast (HC > T2DM), no region showed a significant difference in susceptibility values between the groups. The correlation analysis between susceptibility values and cognitive function scores was tested by voxel-based susceptibility value with sex and age as covariates. After multiple comparison correction, in T2DM patients, the left thalamus showed a significant relationship with TMT-A (R ² = 0.53, P = 0.001). The right thalamus and left thalamus showed a significant relationship with TMT-B (R ² = 0.35, P = 0.019; and R ² = 0.38, P = 0.017, respectively). In HCs, the cluster of right precentral/middle frontal gyrus/inferior frontal gyrus/inferior triangular gyrus showed a significant relationship with TMT-B (R ² = 0.59, P = 0.010). No relationship was found between the susceptibility values with MoCA in the brain region in both two groups.

Conclusion

Patients with T2DM presented declined cognitive assessments and elevated iron deposition in the striatum and frontal lobe, suggesting that executive function decline in T2DM might be associated with the cerebral iron burden and that changes in susceptibility values may represent a latent quantitative imaging marker for early assessment of cognitive decline in patients with T2DM.

Quantifying Genetic and Environmental Influence on Gray Matter Microstructure Using Diffusion MRI

Early neuroimaging work in twin studies focused on studying genetic and environmental influence on gray matter macrostructure. However, it is also important to understand how gray matter microstructure is influenced by genes and environment to facilitate future investigations of their influence in mental disorders. Advanced diffusion MRI (dMRI) measures allow more accurate assessment of gray matter microstructure compared with conventional diffusion tensor measures. To understand genetic and environmental influence on gray matter, we used diffusion and structural MRI data from a large twin and sibling study (N = 840) and computed advanced dMRI measures including return to origin probability (RTOP), which is heavily weighted toward intracellular and intra-axonal restricted spaces, and mean squared displacement (MSD), more heavily weighted to diffusion in extracellular space and large cell bodies in gray matter. We show that while macrostructural features like brain volume are mainly genetically influenced, RTOP and MSD can together tap into both genetic and environmental influence on microstructure.

Fronto-parietal networks underlie the interaction between executive control and conscious perception: Evidence from TMS and DWI

The executive control network is involved in novel situations or those in which prepotent responses need to be overridden. Previous studies have demonstrated that when control is exerted, conscious perception is impaired, and this effect is related to the functional connectivity of fronto-parietal regions. In the present study, we explored the causal involvement of one of the nodes of this fronto-parietal network (the right Supplementary Motor Area, SMA) in the interaction between executive control and conscious perception. Participants performed a dual task in which they responded to a Stroop task while detecting the presence/absence of a near-threshold Gabor stimulus. Concurrently, transcranial magnetic stimulation (TMS) was applied over the right SMA or a control site (vertex; Experiment 1). As a further control, the right Frontal Eye Field (FEF) was stimulated in Experiment 2. Diffusion-weighted imaging (DWI) tractography was used to isolate the three branches of the superior longitudinal fasciculus (SLF I, II and III), and the frontal aslant tract (FAT), and to explore if TMS effects were related to their micro- and macrostructural characteristics. Results demonstrated reduced perceptual sensitivity on incongruent as compared to congruent Stroop trials. A causal role of the right SMA on the modulation of perceptual sensitivity by executive control was only demonstrated when the microstructure of the right SLF III or the left FAT were taken into account. The volume of the right SLF III was also related to the modulation of response criterion by executive control when the right FEF was stimulated. These results add evidence in favor of shared neural correlates for attention and conscious perception in fronto-parietal regions and highlight the role of white matter in TMS effects.

Air Pollution-Related Brain Metal Dyshomeostasis as a Potential Risk Factor for Neurodevelopmental Disorders and Neurodegenerative Diseases

Increasing evidence links air pollution (AP) exposure to effects on the central nervous system structure and function. Particulate matter AP, especially the ultrafine (nanoparticle) components, can carry numerous metal and trace element contaminants that can reach the brain in utero and after birth. Excess brain exposure to either essential or non-essential elements can result in brain dyshomeostasis, which has been implicated in both neurodevelopmental disorders (NDDs; autism spectrum disorder, schizophrenia, and attention deficit hyperactivity disorder) and neurodegenerative diseases (NDGDs; Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis). This review summarizes the current understanding of the extent to which the inhalational or intranasal instillation of metals reproduces in vivo the shared features of NDDs and NDGDs, including enlarged lateral ventricles, alterations in myelination, glutamatergic dysfunction, neuronal cell death, inflammation, microglial activation, oxidative stress, mitochondrial dysfunction, altered social behaviors, cognitive dysfunction, and impulsivity. Although evidence is limited to date, neuronal cell death, oxidative stress, and mitochondrial dysfunction are reproduced by numerous metals. Understanding the specific contribution of metals/trace elements to this neurotoxicity can guide the development of more realistic animal exposure models of human AP exposure and consequently lead to a more meaningful approach to mechanistic studies, potential intervention strategies, and regulatory requirements.

Tracking Inhibitory Control in Youth With ADHD: A Multi-Modal Neuroimaging Approach

BACKGROUND

A decreased ability to inhibit a speeded motor response is a well-studied deficit in Attention Deficit Hyperactivity Disorder (ADHD), and has been proposed as an endophenotype. Inhibitory control has been assessed reliably with the Stop Signal Task (SST) and is associated with prior documented differences in regional brain function using f-MRI. Here, we advance on these findings by examining their structural connectivity and white matter integrity with the goal of identifying a network underlying a core cognitive deficit in ADHD.

METHODS

Healthy controls (N=16) and youth diagnosed with ADHD (N=60) were recruited through the Province of Ontario Neurodevelopmental Disorders Network (POND) and the Hospital for Sick Children. An f-MRI activation difference map was co-registered with each participant's white matter imaging data, representing the specific network nodes where ADHD youth diverged significantly from controls while performing the SST. Probabilistic tractography was applied from these nodes, and white matter integrity indices such as fractional anisotropy (FA) within the tracts of interest were contrasted between the groups and correlated with SST output measures, including the measure of inhibitory control, the stop signal reaction time (SSRT).

RESULTS

The tracts that connected the network nodes belonged primarily to the inferior fronto-occipital fasciculus (IFOF) and cingulum. ADHD subjects showed trend differences in FA compared to controls between right inferior frontal gyrus (IFG) and right superior temporal gyrus (P= 0.09), right IFG and right posterior cingulate (P= 0.01), right anterior cingulate to posterior cingulate (p= 0.08), and between left middle temporal gyrus (BA 39) and left posterior cingulate (P=0.02). A trend correlation was found between radial diffusivity within IFG to STG white matter (IFOF) and SSRT.

CONCLUSIONS

We identified potential white matter tracts related to deficient inhibitory control, elucidating the brain mechanisms of an important cognitive deficit in ADHD. These findings could be integrated into future endophenotypic biomarker studies, incorporating altogether brain structure, function, and behavior for future studies of ADHD and other psychiatric conditions that exhibit this deficit.

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.