Decreased frontal gyrification correlates with altered connectivity in children with autism

Gyrification brain abnormalities as predictors of outcome in anorexia nervosa

Gyrification brain abnormalities are considered a marker of early deviations from normal developmental trajectories and a putative predictor of poor outcome in psychiatric disorders. The aim of this study was to explore cortical folding morphology in patients with anorexia nervosa (AN). A MRI brain study was conducted on 38 patients with AN, 20 fully recovered patients, and 38 healthy women. Local gyrification was measured with procedures implemented in FreeSurfer. Vertex-wise comparisons were carried out to compare: (1) AN patients and healthy women; (2) patients with a full remission at a 3-year longitudinal follow-up assessment and patients who did not recover. AN patients exhibited significantly lower gyrification when compared with healthy controls. Patients with a poor 3-year outcome had significantly lower baseline gyrification when compared to both healthy women and patients with full recovery at follow-up, even after controlling for the effects of duration of illness and gray matter volume. No significant correlation has been found between gyrification, body mass index, amount of weight loss, onset age, and duration of illness. Brain gyrification significantly predicted outcome at follow-up even after controlling for the effects of duration of illness and other clinical prognostic factors. Although the role of starvation in determining our findings cannot be excluded, our study showed that brain gyrification might be a predictor of outcome in AN. Further studies are needed to understand if brain gyrification abnormalities are indices of early neurodevelopmental alterations, the consequence of starvation, or the interaction between both factors.

Reduced Gyrification Is Related to Reduced Interhemispheric Connectivity in Autism Spectrum Disorders

OBJECTIVE

Autism spectrum disorders (ASD) have been associated with atypical cortical gray and subcortical white matter development. Neurodevelopmental theories postulate that a relation between cortical maturation and structural brain connectivity may exist. We therefore investigated the development of gyrification and white matter connectivity and their relationship in individuals with ASD and their typically developing peers.

METHOD

T1- and diffusion-weighted images were acquired from a representative sample of 30 children and adolescents with ASD (aged 8-18 years), and 29 typically developing children matched for age, sex, hand preference, and socioeconomic status. The FreeSurfer suite was used to calculate cortical volume, surface area, and gyrification index. Measures of structural connectivity were estimated using probabilistic tractography and tract-based spatial statistics (TBSS).

RESULTS

Left prefrontal and parietal cortex showed a relative, age-dependent decrease in gyrification index in children and adolescents with ASD compared to typically developing controls. This result was replicated in an age-and IQ-matched sample provided by the Autism Brain Imaging Data Exchange (ABIDE) initiative. Furthermore, tractography and TBSS showed a complementary pattern in which left prefrontal gyrification was negatively related to radial diffusivity in the forceps minor in participants with ASD.

CONCLUSION

The present study builds on earlier findings of abnormal gyrification and structural connectivity in the prefrontal cortex in ASD. It provides a more comprehensive neurodevelopmental characterization of ASD, involving interdependent changes in microstructural white and cortical gray matter. The findings of related abnormal patterns of gyrification and white matter connectivity support the notion of the intertwined development of 2 major morphometric domains in ASD.

Are Molecules Involved in Neuritogenesis and Axon Guidance Related to Autism Pathogenesis?

Autism spectrum disorder is a heterogeneous disease, and numerous alterations of gene expression come into play to attempt to explain potential molecular and pathophysiological causes. Abnormalities of brain development and connectivity associated with alterations in cytoskeletal rearrangement, neuritogenesis and elongation of axons and dendrites might represent or contribute to the structural basis of autism pathology. Slit/Robo signaling regulates cytoskeletal remodeling related to axonal and dendritic branching. Components of its signaling pathway (ABL and Cdc42) are suspected to be molecular bases of alterations of normal development. The present review describes the most important mechanisms underlying neuritogenesis, axon pathfinding and the role of GTPases in neurite outgrowth, with special emphasis on alterations associated with autism spectrum disorders. On the basis of analysis of publicly available microarray data, potential biomarkers of autism are discussed.

MRI Surface-Based Brain Morphometry in Egyptian Autistic and Typically Developing Children

OBJECTIVES

The verbal abilities of autistic children differ from those of typically developing ones and they also differ among autistic children themselves. Neuroanatomical changes and an abnormal organization of functional networks are expected to accompany such a neurodevelopmental disorder. The aim of this study was to delineate the brain neuroanatomical changes in Egyptian children with autism and to compare them with previous studies in order to add more insight into the global brain imaging deviations linked to autism.

PATIENTS AND METHODS

Twenty-five autistic children and 25 typically developing children underwent MRI. Further analysis was performed using surface-based morphometry to obtain cortical thickness, brain volume, and cortical complexity.

RESULTS

MRI analysis results revealed significantly greater cortical thickness, cortical complexity, and gray matter volume in the autistic as compared to the control group. On the other hand, the white matter volume was significantly smaller.

CONCLUSION

These findings generally align with findings in previous studies, except for occasional differences.

Neuroimaging in autism spectrum disorder: brain structure and function across the lifespan

Over the past decade, in-vivo MRI studies have provided many invaluable insights into the neural substrates underlying autism spectrum disorder (ASD), which is now known to be associated with neurodevelopmental variations in brain anatomy, functioning, and connectivity. These systems-level features of ASD pathology seem to develop differentially across the human lifespan so that the cortical abnormalities that occur in children with ASD differ from those noted at other stages of life. Thus, investigation of the brain in ASD poses particular methodological challenges, which must be addressed to enable the comparison of results across studies. Novel analytical approaches are also being developed to facilitate the translation of findings from the research to the clinical setting. In the future, the insights provided by human neuroimaging studies could contribute to biomarker development for ASD and other neurodevelopmental disorders, and to new approaches to diagnosis and treatment.

Shared Brain Connectivity Issues, Symptoms, and Comorbidities in Autism Spectrum Disorder, Attention Deficit/Hyperactivity Disorder, and Tourette Syndrome

The prevalence of neurodevelopmental disorders, including autism spectrum disorder (ASD), attention deficit/hyperactivity disorder (ADHD), and Tourette syndrome (TS), has increased over the past two decades. Currently, about one in six children in the United States is diagnosed as having a neurodevelopmental disorder. Evidence suggests that ASD, ADHD, and TS have similar neuropathology, which includes long-range underconnectivity and short-range overconnectivity. They also share similar symptomatology with considerable overlap in their core and associated symptoms and a frequent overlap in their comorbid conditions. Consequently, it is apparent that ASD, ADHD, and TS diagnoses belong to a broader spectrum of neurodevelopmental illness. Biologically, long-range underconnectivity and short-range overconnectivity are plausibly related to neuronal insult (e.g., neurotoxicity, neuroinflammation, excitotoxicity, sustained microglial activation, proinflammatory cytokines, toxic exposure, and oxidative stress). Therefore, these disorders may a share a similar etiology. The main purpose of this review is to critically examine the evidence that ASD, ADHD, and TS belong to a broader spectrum of neurodevelopmental illness, an abnormal connectivity spectrum disorder, which results from neural long-range underconnectivity and short-range overconnectivity. The review also discusses the possible reasons for these neuropathological connectivity findings. In addition, this review examines the role and issue of axonal injury and regeneration in order to better understand the neuropathophysiological interplay between short- and long-range axons in connectivity issues.

Multicenter mapping of structural network alterations in autism

Autism spectrum disorders (ASD) are a group of neurodevelopmental conditions primarily characterized by abnormalities in social cognition. Abundant previous functional MRI studies have shown atypical activity in networks encompassing medial prefrontal cortex (mPFC) and medial parietal regions corresponding to posterior cingulate cortex and precuneus (PCC/PCU). Conversely, studies assessing structural brain anomalies in ASD have been rather inconsistent. The current work evaluated whether structural changes in ASD can be reliability detected in a large multicenter dataset. Our comprehensive structural MRI framework encompassed cortical thickness mapping and structural covariance analysis based on three independent samples comprising individuals with ASD and controls (n = 220), selected from the Autism Brain Imaging Data Exchange open-access database. Surface-based analysis revealed increased cortical thickness in ASD relative to controls in mPFC and lateral prefrontal cortex. Clusters encompassing mPFC were embedded in altered inter-regional covariance networks, showing decreased covariance in ASD relative to controls primarily to PCC/PCU and inferior parietal regions. Cortical thickness increases and covariance reductions in ASD were consistent, yet of variable effect size, across the different sites evaluated and measurable both in children and adults. Our multisite study shows regional and network-level structural alterations in mPFC in ASD that, possibly, relate to atypical socio-cognitive functions in this condition.

Does degree of gyrification underlie the phenotypic and genetic associations between cortical surface area and cognitive ability?

The phenotypic and genetic relationship between global cortical size and general cognitive ability (GCA) appears to be driven by surface area (SA) and not cortical thickness (CT). Gyrification (cortical folding) is an important property of the cortex that helps to increase SA within a finite space, and may also improve connectivity by reducing distance between regions. Hence, gyrification may be what underlies the SA-GCA relationship. In previous phenotypic studies, a 3-dimensional gyrification index (3DGI) has been positively associated with cognitive ability and negatively associated with mild cognitive impairment, Alzheimer's disease, and psychiatric disorders affecting cognition. However, the differential genetic associations of 3DGI and SA with GCA are still unclear. We examined the heritability of 3DGI, and the phenotypic, genetic, and environmental associations of 3DGI with SA and GCA in a large sample of adult male twins (N = 512). Nearly 85% of the variance in 3DGI was due to genes, and 3DGI had a strong phenotypic and genetic association with SA. Both 3DGI and total SA had positive phenotypic correlations with GCA. However, the SA-GCA correlation remained significant after controlling for 3DGI, but not the other way around. There was also significant genetic covariance between SA and GCA, but not between 3DGI and GCA. Thus, despite the phenotypic and genetic associations between 3DGI and SA, our results do not support the hypothesis that gyrification underlies the association between SA and GCA.

Altered white matter connectivity as a neural substrate for social impairment in Autism Spectrum Disorder

BACKGROUND

Autism Spectrum Disorder (ASD) symptoms have been hypothesized to result from altered brain connectivity. The 'disconnectivity' hypothesis has been used to explain characteristic impairments in socio-emotional function, observed clinically in ASD. Here, we review the evidence for impaired white matter connectivity as a neural substrate for socio-emotional dysfunction in ASD. A review of diffusion tensor imaging (DTI) studies, and focused discussion of relevant post-mortem, structural, and functional neuroimaging studies, is provided.

METHODS

Studies were identified using a sensitive search strategy in MEDLINE, Embase and PsycINFO article databases using the OvidSP database interface. Search terms included database subject headings for the concepts of pervasive developmental disorders, and DTI. Seventy-two published DTI studies examining white matter microstructure in ASD were reviewed. A comprehensive discussion of DTI studies that examined white matter tracts linking socio-emotional structures is presented.

RESULTS

Several DTI studies reported microstructural differences indicative of developmental alterations in white matter organization, and potentially myelination, in ASD. Altered structure within long-range white matter tracts linking socio-emotional processing regions was implicated. While alterations of the uncinate fasciculus and frontal and temporal thalamic projections have been associated with social symptoms in ASD, few studies examined association of tract microstructure with core impairment in this disorder.

CONCLUSIONS

The uncinate fasciculus and frontal and temporal thalamic projections mediate limbic connectivity and integrate structures responsible for complex socio-emotional functioning. Impaired development of limbic connectivity may represent one neural substrate contributing to ASD social impairments. Future efforts to further elucidate the nature of atypical white matter development, and its relationship to core symptoms, may offer new insights into etiological mechanisms contributing to ASD impairments and uncover novel opportunities for targeted intervention.

Multimodal imaging in autism: an early review of comprehensive neural circuit characterization

There is accumulating evidence that the neurobiology of autism spectrum disorders (ASD) is linked to atypical neural communication and connectivity. This body of work emphasizes the need to characterize the function of multiple regions that comprise neural circuits rather than focusing on singular regions as contributing to deficits in ASD. Multimodal neuroimaging - the formal combination of multiple functional and structural measures of the brain - is extremely promising as an approach to understanding neural deficits in ASD. This review provides an overview of the multimodal imaging approach, and then provides a snapshot of how multimodal imaging has been applied in the study of ASD to date. This body of work is separated into two categories: one concerning whole brain connectomics and the other focused on characterizing neural circuits implicated as altered in ASD. We end this review by highlighting emerging themes from the existing body of literature, and new resources that will likely influence future multimodal imaging studies.

A Two-Hit Model of Autism: Adolescence as the Second Hit

Adolescence brings dramatic changes in behavior and neural organization. Unfortunately, for some 30% of individuals with autism, there is marked decline in adaptive functioning during adolescence. We propose a two-hit model of autism. First, early perturbations in neural development function as a "first hit" that sets up a neural system that is "built to fail" in the face of a second hit. Second, the confluence of pubertal hormones, neural reorganization, and increasing social demands during adolescence provides the "second hit" that interferes with the ability to transition into adult social roles and levels of adaptive functioning. In support of this model, we review evidence about adolescent-specific neural and behavioral development in autism. We conclude with predictions and recommendations for empirical investigation about several domains in which developmental trajectories for individuals with autism may be uniquely deterred in adolescence.

Prefrontal cortex, hippocampus, and basolateral amygdala plasticity in a rat model of autism spectrum

We aimed to investigate the effect of prenatal administration of valproic acid (VPA) (500 mg/kg) at embryonic day 12.5 on the anatomical properties of the prefrontal cortex, hippocampus, and basolateral amygdala, at three different ages: immediately after weaning (postnatal day 21 [PD21]), prepubertal (PD35), and postpubertal (PD70) ages in a rat model of autistic spectrum disorder. Quantitative analysis of the thickness of the prefrontal cortex revealed a reduced size at all study ages in the cingulate 1 area of the prefrontal cortex and CA1 of the dorsal hippocampus in prenatally exposed animals compared to controls. At the level of the basolateral amygdala, a reduction in the size was observed at PD35 and PD70 in the VPA group. In addition, a reduced thickness was observed in the prelimbic region of the prefrontal cortex in VPA animals at PD35. Interestingly, no differences in cortical thickness were observed between control and VPA animals in the infralimbic region of the prefrontal at any age. Our results suggest that prenatal exposure to VPA differentially alters cortical limbic regions anatomical parameters, with implication in the autistic spectrum disorder.

Multimodal brain imaging in autism spectrum disorder and the promise of twin research

Current evidence suggests the phenotype of autism spectrum disorder to be driven by a complex interaction of genetic and environmental factors impacting onto brain maturation, synaptic function, and cortical networks. However, findings are heterogeneous, and the exact neurobiological pathways of autism spectrum disorder still remain poorly understood. The co-twin control or twin-difference design is a potentially powerful tool to disentangle causal genetic and environmental contributions on neurodevelopment in autism spectrum disorder. To this end, monozygotic twins discordant for this condition provide unique means for the maximum control of potentially confounding factors. Unfortunately, only few studies of a rather narrow scope, and limited sample size, have been conducted. In an attempt to highlight the great potential of combining the brain connectome approach with monozygotic twin design, we first give an overview of the existing neurobiological evidence for autism spectrum disorder and its cognitive correlates. Then, a special focus is made onto the brain imaging findings reported within populations of monozygotic twins phenotypically discordant for autism spectrum disorder. Finally, we introduce the brain connectome model and describe an ongoing project using this approach among the largest cohort of monozygotic twins discordant for autism spectrum disorder ever recruited.