Magnetic resonance imaging study of the brain in autism

Understanding the relationship between cerebellar structure and social abilities

BACKGROUND

The cerebellum contains more than 50% of all neurons in the brain and is involved in a broad range of cognitive functions, including social communication and social cognition. Inconsistent atypicalities in the cerebellum have been reported in individuals with autism compared to controls suggesting the limits of categorical case control comparisons. Alternatively, investigating how clinical dimensions are related to neuroanatomical features, in line with the Research Domain Criteria approach, might be more relevant. We hypothesized that the volume of the "cognitive" lobules of the cerebellum would be associated with social difficulties.

METHODS

We analyzed structural MRI data from a large pediatric and transdiagnostic sample (Healthy Brain Network). We performed cerebellar parcellation with a well-validated automated segmentation pipeline (CERES). We studied how social communication abilities-assessed with the social component of the Social Responsiveness Scale (SRS)-were associated with the cerebellar structure, using linear mixed models and canonical correlation analysis.

RESULTS

In 850 children and teenagers (mean age 10.8 ± 3 years; range 5-18 years), we found a significant association between the cerebellum, IQ and social communication performance in our canonical correlation model.

LIMITATIONS

Cerebellar parcellation relies on anatomical boundaries, which does not overlap with functional anatomy. The SRS was originally designed to identify social impairments associated with autism spectrum disorders.

CONCLUSION

Our results unravel a complex relationship between cerebellar structure, social performance and IQ and provide support for the involvement of the cerebellum in social and cognitive processes.

Translating neuroimaging changes to neuro-endophenotypes of autistic spectrum disorder: a narrative review

Background

Autism-spectrum disorder is a neurodevelopmental disorder with heterogeneity in etiopathogenesis and clinical presentation. Neuroanatomical and neurophysiological abnormalities may represent neural endophenotypes for autism spectrum disorders which may help identify subgroups of patients seemingly similar in clinical presentation yet different in their pathophysiological underpinnings. Furthermore, a thorough understanding of the pathophysiology of disease can pave the way to effective treatments, prevention, and prognostic predictions. The aim of this review is to identify the predominant neural endophenotypes in autism-spectrum disorder. The evidence was researched at the following electronic databases: Pubmed, PsycINFO, Scopus, Web of Science, and EMBASE.

Results

Enlarged brain, especially frontotemporal cortices have been consistently reported by structural neuroimaging, whereas functional neuroimaging has revealed frontotemporal dysconnectivity.

Conclusions

Regrettably, many of these findings have not been consistent. Therefore, translating these findings into neural endophenotype is by far an attempt in its budding stage. The structural and functional neuroimaging changes may represent neural endophenotypes unique to autism-spectrum disorder. Despite inconsistent results, a clinically meaningful finding may require combined efforts of autism-spectrum-disorder researchers focused on different aspects of basic, genetic, neuroimaging, and clinical research.

Altered transcallosal fiber count and volume in high-functioning adults with autism spectrum disorder

An altered pattern of information processing has been hypothesized in autism spectrum disorder (ASD), characterized by enhanced local network connectivity and reduced long-distance communication. Previous findings of impaired white matter integrity in the genu and the body of the corpus callosum already indicated reduced long-distance connectivity in patients with ASD. However, it remained unclear how this reduced white matter integrity affects the structural connectivity of the corresponding brain areas. To this end, we analyzed magnetic resonance images (MRI) from 30 participants with high-functioning ASD and 30 typically developed individuals using a global tracking approach to estimate the fiber count and volume of the transcallosal fiber tracts of the five corpus callosum subsections. A reduced fiber count and fiber volume in the anterior subsection of the corpus callosum was detected, supporting the hypothesis of reduced long-distance connectivity in ASD.

Neuroanatomy and behavior in mice with a haploinsufficiency of AT-rich interactive domain 1B (ARID1B) throughout development

BACKGROUND

One of the causal mechanisms underlying neurodevelopmental disorders (NDDs) is chromatin modification and the genes that regulate chromatin. AT-rich interactive domain 1B (ARID1B), a chromatin modifier, has been linked to autism spectrum disorder and to affect rare and inherited genetic variation in a broad set of NDDs.

METHODS

A novel preclinical mouse model of Arid1b deficiency was created and validated to characterize and define neuroanatomical, behavioral and transcriptional phenotypes. Neuroanatomy was assessed ex vivo in adult animals and in vivo longitudinally from birth to adulthood. Behavioral testing was also performed throughout development and tested all aspects of motor, learning, sociability, repetitive behaviors, seizure susceptibility, and general milestones delays.

RESULTS

We validated decreased Arid1b mRNA and protein in Arid1b+/- mice, with signatures of increased axonal and synaptic gene expression, decreased transcriptional regulator and RNA processing expression in adult Arid1b+/- cerebellum. During neonatal development, Arid1b+/- mice exhibited robust impairments in ultrasonic vocalizations (USVs) and metrics of developmental growth. In addition, a striking sex effect was observed neuroanatomically throughout development. Behaviorally, as adults, Arid1b+/- mice showed low motor skills in open field exploration and normal three-chambered approach. Arid1b+/- mice had learning and memory deficits in novel object recognition but not in visual discrimination and reversal touchscreen tasks. Social interactions in the male-female social dyad with USVs revealed social deficits on some but not all parameters. No repetitive behaviors were observed. Brains of adult Arid1b+/- mice had a smaller cerebellum and a larger hippocampus and corpus callosum. The corpus callosum increase seen here contrasts previous reports which highlight losses in corpus callosum volume in mice and humans.

LIMITATIONS

The behavior and neuroimaging analyses were done on separate cohorts of mice, which did not allow a direct correlation between the imaging and behavioral findings, and the transcriptomic analysis was exploratory, with no validation of altered expression beyond Arid1b.

CONCLUSIONS

This study represents a full validation and investigation of a novel model of Arid1b+/- haploinsufficiency throughout development and highlights the importance of examining both sexes throughout development in NDDs.

Potential role of genomic imprinted genes and brain developmental related genes in autism

BACKGROUND

Autism is a complex disease involving both environmental and genetic factors. Recent efforts have implicated the correlation of genomic imprinting and brain development in autism, however the pathogenesis of autism is not completely clear. Here, we used bioinformatic tools to provide a comprehensive analysis of the autism-related genes, genomic imprinted genes and the spatially and temporally differentially expressed genes of human brain, aiming to explore the relationship between autism, brain development and genomic imprinting.

METHODS

This study analyzed the distribution correlation between autism-related genes and imprinted genes on chromosomes using sliding windows and statistical methods. The normal brains' gene expression microarray data were reanalyzed to construct a spatio-temporal coordinate system of gene expression during brain development. Finally, we intersected the autism-related genes, imprinted genes and brain spatio-temporally differentially expressed genes for further analysis to find the major biological processes that these genes involved.

RESULTS

We found a positive correlation between the autism-related genes' and imprinted genes' distribution on chromosomes. Through the analysis of the normal brain microarray data, we constructed a spatio-temporal coordinate system of gene expression during human brain development, and obtained 13 genes that are differentially expressed in the process of brain development, which are both autism-related genes and imprinted genes. Furthermore, enrichment analysis illustrated that these genes are mainly involved in the biological processes, such as gamma-aminobutyric acid signaling pathway, neuron recognition, learning or memory, and regulation of synaptic transmission. Bioinformatic analysis implied that imprinted genes regulate the development and behavior of the brain. And its own mutation or changes in the epigenetic modification state of the imprinted control region could lead to some diseases, indicating that imprinted genes and brain development play an important role in diagnosis and prognosis of autism.

CONCLUSION

This study systematically correlates brain development and genomic imprinting with autism, which provides a new perspective for the study of genetic mechanisms of autism, and selected the potential candidate biomarkers for early diagnosis of autism in clinic.

Hyperactivity and depression-like traits in Bax KO mice

The Bax gene is a member of the Bcl-2 gene family and its pro-apoptotic Bcl-associated X (Bax) protein is believed to be crucial in regulating apoptosis during neuronal development as well as following injury. With the advent of mouse genomics, mice lacking the pro-apoptotic Bax gene (Bax KO) have been extensively used to study how cell death helps to determine synaptic circuitry formation during neurodevelopment and disease. Surprisingly, in spite of its wide use and the association of programmed neuronal death with motor dysfunctions and depression, the effects of Bax deletion on mice spontaneous locomotor activity and depression-like traits are unknown. Here we examine the behavioral characteristics of Bax KO male mice using classical paradigms to evaluate spontaneous locomotor activity and depressive-like responses. In the open field, Bax KO animals exhibited greater locomotor activity than their control littermates. In the forced swimming test, Bax KO mice displayed greater immobility times, a behavior despair state, when compared to controls. Collectively, our findings corroborate the notion that a fine balance between cell survival and death early during development is critical for normal brain function later in life. Furthermore, it points out the importance of considering depressive-like and hyperactivity behavioral phenotypes when conducting neurodevelopmental and other studies using the Bax KO strain.

Neuroimaging endophenotypes in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that has a strong genetic basis, and is heterogeneous in its etiopathogenesis and clinical presentation. Neuroimaging studies, in concert with neuropathological and clinical research, have been instrumental in delineating trajectories of development in children with ASD. Structural neuroimaging has revealed ASD to be a disorder with general and regional brain enlargement, especially in the frontotemporal cortices, while functional neuroimaging studies have highlighted diminished connectivity, especially between frontal-posterior regions. The diverse and specific neuroimaging findings may represent potential neuroendophenotypes, and may offer opportunities to further understand the etiopathogenesis of ASD, predict treatment response, and lead to the development of new therapies.

Altered functional connectivity of the language network in ASD: role of classical language areas and cerebellum

The development of language, social interaction and communicative skills is remarkably different in the child with autism spectrum disorder (ASD). Atypical brain connectivity has frequently been reported in this patient population. However, the neural correlates underlying their disrupted language development and functioning are still poorly understood. Using resting state fMRI, we investigated the functional connectivity properties of the language network in a group of ASD patients with clear comorbid language impairment (ASD-LI; N = 19) and compared them to the language related connectivity properties of 23 age-matched typically developing children. A verb generation task was used to determine language components commonly active in both groups. Eight joint language components were identified and subsequently used as seeds in a resting state analysis. Interestingly, both the interregional and the seed-based whole brain connectivity analysis showed preserved connectivity between the classical intrahemispheric language centers, Wernicke's and Broca's areas. In contrast however, a marked loss of functional connectivity was found between the right cerebellar region and the supratentorial regulatory language areas. Also, the connectivity between the interhemispheric Broca regions and modulatory control dorsolateral prefrontal region was found to be decreased. This disruption of normal modulatory control and automation function by the cerebellum may underlie the abnormal language function in children with ASD-LI.

Detecting abnormalities of corpus callosum connectivity in autism using magnetic resonance imaging and diffusion tensor tractography

The corpus callosum (CC) has emerged as one of the primary targets of autism research. To detect aberrant CC interhemispheric connectivity in autism, we performed T1-weighted magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI)-based tractography in 18 children with high functioning autism (HFA) and 16 well-matched typically developing (TD) children. We compared global and regional T1 measures (CC volume, and CC density), and the DTI measures [fractional anisotropy (FA), apparent diffusion coefficient (ADC), average fiber length (AFL), and fiber number (FN)] of transcallosal fibers, between the two groups. We also evaluated the relationships between scores on the Childhood Autism Rating Scale (CARS) and CC T1 or DTI measurements. Significantly less white matter density in the anterior third of the CC, and higher ADC and lower FN values of the anterior third transcallosal fiber tracts were found in HFA patients compared to TD children. These results suggested that the anterior third CC density and transcallosal fiber connectivity were affected in HFA children.

Role of CpG context and content in evolutionary signatures of brain DNA methylation

DNA methylation is essential in brain function and behavior; therefore, understanding the role of DNA methylation in brain-based disorders begins with the study of DNA methylation profiles in normal brain. Determining the patterns and scale of methylation conservation and alteration in an evolutionary context enables the design of focused but effective methylation studies of disease states. We applied an enzymatic-based approach, Methylation Mapping Analysis by Paired-end Sequencing (Methyl-MAPS), which utilizes second-generation sequencing technology to provide an unbiased representation of genome-wide DNA methylation profiles of human and mouse brains. In this large-scale study, we assayed CpG methylation in cerebral cortex of neurologically and psychiatrically normal human postmortem specimens, as well as mouse forebrain specimens. Cross-species human-mouse DNA methylation conservation analysis shows that DNA methylation is not correlated with sequence conservation. Instead, greater DNA methylation conservation is correlated with increasing CpG density. In addition to CpG density, these data show that genomic context is a critical factor in DNA methylation conservation and alteration signatures throughout mammalian brain evolution. We identify key genomic features that can be targeted for identification of epigenetic loci that may be developmentally and evolutionarily conserved and wherein aberrations in DNA methylation patterns can confer risk for disease.

The neuropathology of autism: defects of neurogenesis and neuronal migration, and dysplastic changes

Autism is characterized by a broad spectrum of clinical manifestations including qualitative impairments in social interactions and communication, and repetitive and stereotyped patterns of behavior. Abnormal acceleration of brain growth in early childhood, signs of slower growth of neurons, and minicolumn developmental abnormalities suggest multiregional alterations. The aim of this study was to detect the patterns of focal qualitative developmental defects and to identify brain regions that are prone to developmental alterations in autism. Formalin-fixed brain hemispheres of 13 autistic (4–60 years of age) and 14 age-matched control subjects were embedded in celloidin and cut into 200-μm-thick coronal sections, which were stained with cresyl violet and used for neuropathological evaluation. Thickening of the subependymal cell layer in two brains and subependymal nodular dysplasia in one brain is indicative of active neurogenesis in two autistic children. Subcortical, periventricular, hippocampal and cerebellar heterotopias detected in the brains of four autistic subjects (31%) reflect abnormal neuronal migration. Multifocal cerebral dysplasia resulted in local distortion of the cytoarchitecture of the neocortex in four brains (31%), of the entorhinal cortex in two brains (15%), of the cornu Ammonis in four brains and of the dentate gyrus in two brains. Cerebellar flocculonodular dysplasia detected in six subjects (46%), focal dysplasia in the vermis in one case, and hypoplasia in one subject indicate local failure of cerebellar development in 62% of autistic subjects. Detection of flocculonodular dysplasia in only one control subject and of a broad spectrum of focal qualitative neuropathological developmental changes in 12 of 13 examined brains of autistic subjects (92%) reflects multiregional dysregulation of neurogenesis, neuronal migration and maturation in autism, which may contribute to the heterogeneity of the clinical phenotype.

Development of large-scale functional brain networks in children

Large-scale rewiring of brain circuits in children leads to emergence of hierarchical organization in the mature adult brain.

The ontogeny of large-scale functional organization of the human brain is not well understood. Here we use network analysis of intrinsic functional connectivity to characterize the organization of brain networks in 23 children (ages 7–9 y) and 22 young-adults (ages 19–22 y). Comparison of network properties, including path-length, clustering-coefficient, hierarchy, and regional connectivity, revealed that although children and young-adults' brains have similar “small-world” organization at the global level, they differ significantly in hierarchical organization and interregional connectivity. We found that subcortical areas were more strongly connected with primary sensory, association, and paralimbic areas in children, whereas young-adults showed stronger cortico-cortical connectivity between paralimbic, limbic, and association areas. Further, combined analysis of functional connectivity with wiring distance measures derived from white-matter fiber tracking revealed that the development of large-scale brain networks is characterized by weakening of short-range functional connectivity and strengthening of long-range functional connectivity. Importantly, our findings show that the dynamic process of over-connectivity followed by pruning, which rewires connectivity at the neuronal level, also operates at the systems level, helping to reconfigure and rebalance subcortical and paralimbic connectivity in the developing brain. Our study demonstrates the usefulness of network analysis of brain connectivity to elucidate key principles underlying functional brain maturation, paving the way for novel studies of disrupted brain connectivity in neurodevelopmental disorders such as autism.

The disruption of normal brain organization in humans is believed to underlie a number of behavioral conditions, such as autism spectrum disorders (ASD) and attention-deficit/hyperactivity disorder (ADHD). To gain insight into how normal brain organization develops, we mapped functional brain connectivity in children and young adults, and used a network analysis to characterize and compare the organization of brain networks. Comparison of network properties revealed that while children and young adults' brains have similar organization at the global level, there were several key differences in connectivity. For example, children's brains had less of a hierarchical organization than young-adults. Most importantly, we show that the dynamic process of over-connectivity followed by pruning, which rewires connectivity at the neuronal level, also operates at the systems level, reconfiguring and rebalancing subcortical and paralimbic connectivity in the developing brain. Our findings demonstrate the utility of using network analyses of multimodal brain connectivity to study maturation of brain circuits, and suggest new avenues for future research on neurodevelopmental disorders such as ASD and ADHD.

GABA(A) receptor downregulation in brains of subjects with autism

Gamma-aminobutyric acid A (GABA(A)) receptors are ligand-gated ion channels responsible for mediation of fast inhibitory action of GABA in the brain. Preliminary reports have demonstrated altered expression of GABA receptors in the brains of subjects with autism suggesting GABA/glutamate system dysregulation. We investigated the expression of four GABA(A) receptor subunits and observed significant reductions in GABRA1, GABRA2, GABRA3, and GABRB3 in parietal cortex (Brodmann's Area 40 (BA40)), while GABRA1 and GABRB3 were significantly altered in cerebellum, and GABRA1 was significantly altered in superior frontal cortex (BA9). The presence of seizure disorder did not have a significant impact on GABA(A) receptor subunit expression in the three brain areas. Our results demonstrate that GABA(A) receptors are reduced in three brain regions that have previously been implicated in the pathogenesis of autism, suggesting widespread GABAergic dysfunction in the brains of subjects with autism.

Expression of astrocytic markers aquaporin 4 and connexin 43 is altered in brains of subjects with autism

Neuroanatomical studies have revealed extensive structural brain abnormalities in subjects with autism. Recently, studies have provided evidence of neuroglial responses and neuroinflammation in autism. The current study investigated whether two astrocytic markers, aquaporin 4 and connexin 43, are altered in brains from subjects with autism. Postmortem brain tissues from Brodmann's Area 40 (BA40, parietal cortex), Brodmann's Area 9 (BA9, superior frontal cortex), and cerebella of subjects with autism and matched controls were subject to SDS-PAGE and western blotting. Connexin 43 expression was increased significantly in BA9. Aquaporin 4 expression was decreased significantly in cerebellum. These data suggest that changes are apparent in markers for abnormal glial-neuronal communication (connexin 43 and aquaporin 4) in brains of subjects with autism.

Gene expression changes in children with autism

The objective of this study was to identify gene expression differences in blood differences in children with autism (AU) and autism spectrum disorder (ASD) compared to general population controls. Transcriptional profiles were compared with age- and gender-matched, typically developing children from the general population (GP). The AU group was subdivided based on a history of developmental regression (A-R) or a history of early onset (A-E without regression). Total RNA from blood was processed on human Affymetrix microarrays. Thirty-five children with AU (17 with early onset autism and 18 with autism with regression) and 14 ASD children (who did not meet criteria for AU) were compared to 12 GP children. Unpaired t tests (corrected for multiple comparisons with a false discovery rate of 0.05) detected a number of genes that were regulated more than 1.5-fold for AU versus GP (n=55 genes), for A-E versus GP (n=140 genes), for A-R versus GP (n=20 genes), and for A-R versus A-E (n=494 genes). No genes were significantly regulated for ASD versus GP. There were 11 genes shared between the comparisons of all autism subgroups to GP (AU, A-E, and A-R versus GP) and these genes were all expressed in natural killer cells and many belonged to the KEGG natural killer cytotoxicity pathway (p=0.02). A subset of these genes (n=7) was tested with qRT-PCR and all genes were found to be differentially expressed (p<0.05). We conclude that the gene expression data support emerging evidence for abnormalities in peripheral blood leukocytes in autism that could represent a genetic and/or environmental predisposition to the disorder.

Neural dynamics of autistic behaviors: cognitive, emotional, and timing substrates

What brain mechanisms underlie autism, and how do they give rise to autistic behavioral symptoms? This article describes a neural model, called the Imbalanced Spectrally Timed Adaptive Resonance Theory (iSTART) model, that proposes how cognitive, emotional, timing, and motor processes that involve brain regions such as the prefrontal and temporal cortex, amygdala, hippocampus, and cerebellum may interact to create and perpetuate autistic symptoms. These model processes were originally developed to explain data concerning how the brain controls normal behaviors. The iSTART model shows how autistic behavioral symptoms may arise from prescribed breakdowns in these brain processes, notably a combination of underaroused emotional depression in the amygdala and related affective brain regions, learning of hyperspecific recognition categories in the temporal and prefrontal cortices, and breakdowns of adaptively timed attentional and motor circuits in the hippocampal system and cerebellum. The model clarifies how malfunctions in a subset of these mechanisms can, through a systemwide vicious circle of environmentally mediated feedback, cause and maintain problems with them all.

Cognitive and behavioural characteristics in blind children with bilateral optic nerve hypoplasia

AIM

To describe cognitive and behavioural characteristics in a group of blind children with bilateral optic nerve hypoplasia (ONH).

METHODS

Data from records, parents, teachers, and repeated developmental assessments of 13 blind children with ONH born in 1988-1998 were analysed. All children had neuroimaging and/or hormonal evidence of midline malformations. They were all blind and able to communicate with speech.

RESULTS

Severe mood swings and temper tantrums were common, especially during the first years of life. Later in life, sluggish tempo, low frustration tolerance and a narrow range of interests were common. Autism had been diagnosed in 6/13 children, autistic-like condition (ALC) was found in another three. The behaviour of the remaining four children was not within the autism spectrum. Eight children had cognitive capacities within the normal or near-normal range; five had mental retardation. Autism/ALC was found in all cognitive subgroups. All children exhibited fluent speech and, of these, 12 had started to talk at the expected age, but had clear deficiencies in communicative ability.

CONCLUSION

These children had a common pattern of behavioural characteristics including autism spectrum disorders independent of intellectual capacities.

A question of balance: a proposal for new mouse models of autism

Autism spectrum disorder (ASD) represents a major mental health problem with estimates of prevalence ranging from 1/500 to 1/2000. While generally recognized as developmental in origin, little to nothing is certain about its etiology. Currently, diagnosis is made on the basis of a variety of early developmental delays and/or regressions in behavior. There are no universally agreed upon changes in brain structure or cell composition. No biomarkers of any type are available to aid or confirm the clinical diagnosis. In addition, while estimates of the heritability of the condition range from 60 to 90%, as of this writing no disease gene has been unequivocally identified. The prevalence of autism is three- to four-fold higher in males than in females, but the reason for this sexual dimorphism is unknown. In light of all of these ambiguities, a proposal to discuss potential animal models may seem the heart of madness. However, parsing autism into its individual genetic, behavioral, and neurobiological components has already facilitated a 'conversation' between the human disease and the neuropathology and biochemistry underlying the disorder. Building on these results, it should be possible to not just replicate one aspect of autism but to connect the developmental abnormalities underlying the ultimate behavioral phenotype. A reciprocal conversation such as this, wherein the human disease informs on how to make a better animal model and the animal model teaches of the biology causal to autism, would be highly beneficial.

Neuronal nitric oxide synthase expression in cerebellar mutant mice

Nitric oxide (NO) is a diffusible, multifunctional signaling molecule found in many areas of the brain. NO signaling is involved in a wide array of neurophysiological functions including synaptogenesis, modulation of neurotransmitter release, synaptic plasticity, central nervous system blood flow and cell death. NO synthase (NOS) activity regulates the production of NO and the cerebellum expresses high levels of nitric oxide synthase (NOS) in granule, stellate and basket cells. Cerebellar mutant mice provide excellent opportunities to study changes of NO/NOS concentrations and activities to gain a greater understanding of the roles of NO and NOS in cerebellar function. Here, we have reviewed the current understanding of the functional roles of NO and NOS in the cerebellum and present NO/NOS activities that have been described in various cerebellar mutant mice and NOS knockout mice. NO appears to exert neuroprotective effects at low to moderate concentrations, whereas NO becomes neurotoxic as the concentration increases. Excessive NO production can cause oxidative stress to neurons, ultimately impairing neuronal function and result in neuronal cell death. Based on their genetics and cerebellar histopathology, some of cerebellar mutant mice display similarities with human neurological conditions and may prove to be valuable models to study several human neurological disorders, such as autism and schizophrenia.

Dynamic mapping of human cortical development during childhood through early adulthood

We report the dynamic anatomical sequence of human cortical gray matter development between the age of 4-21 years using quantitative four-dimensional maps and time-lapse sequences. Thirteen healthy children for whom anatomic brain MRI scans were obtained every 2 years, for 8-10 years, were studied. By using models of the cortical surface and sulcal landmarks and a statistical model for gray matter density, human cortical development could be visualized across the age range in a spatiotemporally detailed time-lapse sequence. The resulting time-lapse "movies" reveal that (i) higher-order association cortices mature only after lower-order somatosensory and visual cortices, the functions of which they integrate, are developed, and (ii) phylogenetically older brain areas mature earlier than newer ones. Direct comparison with normal cortical development may help understanding of some neurodevelopmental disorders such as childhood-onset schizophrenia or autism.

Postural stability in children with autism spectrum disorder

Maintaining upright posture is a complex process involving multiple afferent systems. The aim of this study was to measure the postural stability of children with Autism Spectrum Disorder (ASD) compared with children with typical neurodevelopment and to measure the relative contributions of the visual, somatosensory, and vestibular afferent systems in each group. Eight boys with ASD and eight age-, race-, and gender-matched controls participated in this study using force platform technology with customized software to measure postural sway under conditions designed to eliminate or modify visual and somatosensory input. Children with ASD had significantly larger sway areas under all test conditions in which afferent input was modified. These results are consistent with a deficit in the integration of visual, vestibular, and somatosensory input to maintain postural orientation.

Alterações anátomo-funcionais do sistema nervoso central no transtorno autístico: um estudo com RNM e SPECT

Apresentamos um estudo das alterações anátomo-funcionais do sistema nervoso central (SNC) de pacientes com transtorno autístico (TA), através da ressonância nuclear magnética (RNM) e da tomografia computadorizada por emissão de fóton único (SPECT). Foram estudados 24 pacientes, sendo 15 (62,5%) do sexo masculino e 9 (17,5%) do feminino, com idade média de 9 anos. Todos os pacientes foram submetidos à RNM e apenas em 19 foi realizado o SPECT. Dos pacientes que realizaram RNM, 75% apresentaram alterações anatômicas e dos que realizaram o SPECT todos apresentaram alterações funcionais. As alterações anatômicas estavam preferencialmente localizadas no corpo caloso (25%), septo pelúcido (15,63%), ventrículos cerebrais (12,55%), cerebelo (9,38%), lobo temporal (6,25%), lobo occipital (6,25%) e hipocampo (6,25%). As alterações funcionais predominaram no lobo frontal (53,13%), lobo temporal (28,13%) , lobo parietal (15,63%) e nos núcleos da base (3,13%). A presença de alterações anátomo-funcionais do SNC não são prioritárias para o diagnóstico, o qual deve ter sempre uma validação clínica.

The cerebellum and spatial ability: dissection of motor and cognitive components with a mouse model system

The cerebellum has recently been linked to spatial navigation, as indicated by the inferior performance of cerebellar mutant or cerebellar lesioned animals in the water maze. The inability to dissociate motor from cognitive deficits in the impaired water maze performance has been a confounding variable in previous studies, however. In this study, we sought to define clearly the role of the cerebellar system in spatial navigation outside of motor control by creating a mouse model of Purkinje cell loss with intact motor ability, and testing these mice in the water maze. To this end, we made aggregation chimeras between Lc/+ mice, which lose all Purkinje cells postnatally, and +/+ control mice. Lc/+ mice are ataxic and show impaired rotor-rod performance. By contrast, we show that Lc/+ left arrow over right arrow +/+ chimeras above a threshold of Purkinje cell loss show no outward signs of motor impairment and demonstrated normal rotor-rod ability. In the water maze, we found that Lc/+ mice showed impaired performance in the place, cue and platform removal tasks, whereas Lc/+ left arrow over right arrow +/+ chimeras performed similarly to controls in all tasks. We found that the impaired performance in the water maze of Lc/+ mice resulted from both motor as well as cognitive impairment that could be separated from one another by statistical means. In addition, through the analysis of individual chimeric mice, the relationships between these deficits and the total number of Purkinje cells were determined and a specific role for Purkinje cells in search strategy was identified.

Autism: a large unmet medical need and a complex research problem

Autism has been becoming the focus of attention as its apparently increasing prevalence is better appreciated. According to some estimates, the frequency of children with autistic spectrum disorder (ASD) can be as high as 1 in 150. The diagnosis can be made as early as 2 years of age, and autistic patients often have a normal life span. Thus, in terms of the number of "patient years," ASD represents a market that is as large as that of the biggest neurological indication, Alzheimer's disease. Despite the clear unmet medical need, no effective treatment is available. This may be because the mechanism of ASD is not understood. The aim of the present paper is to review recent advances in autism research and to discuss some of the most stressing problems mainly from a preclinical research standpoint. We hope to draw attention to the need to study this devastating disease that places an enormous burden on the society in general and the relatives and caregivers of autistic patients in particular.

Specificity of cerebellar vermian abnormalities in autism: a quantitative magnetic resonance imaging study

To gain insight into the specificity of cerebellar vermian abnormalities reported in autism, we conducted a magnetic resonance imaging (MRI) study of boys with either of two conditions associated with autism, Down syndrome and fragile X syndrome, compared with boys with idiopathic autism and controls. The subjects, ranging in age from 3 to 9 years, included 16 boys with Down syndrome + autism and 11 boys with Down syndrome only; 13 boys with fragile X syndrome + autism and 9 boys with fragile X syndrome only; 10 boys with idiopathic autism; and 22 controls. Diagnosis of autism was based on DSM-IV criteria, confirmed primarily by the Autism Diagnostic Interview. T1-weighted midsagittal MRIs were used to measure midline structures. Intracranial area, reflecting brain size, was significantly smaller in subjects with Down syndrome. Therefore, all vermian measures were expressed as ratios to intracranial area. Analysis of covariance (covarying for age and IQ) demonstrated that posterior vermi (lobules VI-VII and VIII-X) were markedly smaller in both Down syndrome groups and those with fragile X syndrome only, whereas only lobules VI-VII were reduced in idiopathic autism. Factorial analyses of variance tested interactions between autism factor and the diagnosis of Down syndrome or fragile X syndrome. The size of lobules VI-VII/intracranial area was dependent on autism status only in fragile X syndrome, with ratios significantly larger in fragile X syndrome with autism with respect to fragile X syndrome only. We conclude that selective posterior vermis hypoplasia is seen not only in idiopathic autism but also in Down syndrome and some individuals with fragile X syndrome. However, reductions in vermian lobules VI and VII appear to be specific to idiopathic autism, whereas increased size of lobules VI and VII is associated with autism in fragile X syndrome. The latter results are consistent with MRI studies showing lobules VI-VII hyperplasia in a subset of subjects with idiopathic autism and cerebral and hippocampal enlargements in fragile X syndrome.

Glutamic acid decarboxylase 65 and 67 kDa proteins are reduced in autistic parietal and cerebellar cortices

BACKGROUND

A limited number of reports have demonstrated abnormalities involving the glutamate and gamma amino butyric acid systems in blood and platelets of subjects with autism. To further investigate these studies, brain levels of rate limiting enzyme, glutamic acid decarboxylase, which is responsible for normal conversion of glutamate to gamma amino butyric acid in the brain, were investigated.

METHODS

Postmortem cerebellar and parietal cortices of age (mean +/- SD for controls 23 +/- 4.2, autistic 25.2 +/- 5.2 cerebellum; controls 23.5 +/- 4.8, autistic 21.6 +/- 3.8 parietal cortex), gender and postmortem interval-matched autistic and control subjects (n = 8 control, n = 5 autism, cerebellum; n = 4 control, n = 5 autism, parietal cortex) were subjected to SDS-PAGE and western blotting. Brain levels of glutamic acid decarboxylase proteins of 65 and 67 kDa and beta-actin were determined.

RESULTS

Glutamic acid decarboxylase protein of 65 kDa was reduced by 48% and 50% in parietal and cerebellar (p <.02) areas of autistic brains versus controls respectively. By the same token, glutamic acid decarboxylase protein of 67 kDa was reduced by 61% and 51% in parietal (p <.03) and cerebellar areas of autistic brains versus controls respectively. Brain levels of beta-actin were essentially similar in both groups.

CONCLUSIONS

The observed reductions in glutamic acid decarboxylase 65 and 67 kDa levels may account for reported increases of glutamate in blood and platelets of autistic subjects. Glutamic acid decarboxylase deficiency may be due to or associated with abnormalities in levels of glutamate/gamma amino butyric acid, or transporter/receptor density in autistic brain.

Effects of age on brain volume and head circumference in autism

OBJECTIVE

To determine whether brain volume, as assessed on MRI scans, differs between individuals with autism and control subjects, and whether such differences are affected by age.

BACKGROUND

Previous studies have found increased brain weight, head circumference, and MRI brain volume in children with autism. However, studies of brain size in adults with autism have yielded conflicting results. The authors hypothesize that enlargement of the brain may be a feature of brain development during early childhood in autism that normalizes with maturational processes.

METHODS

The authors measured total brain volumes from 1.5-mm coronal MRI scans in 67 non-mentally retarded children and adults with autism and 83 healthy community volunteers, ranging in age from 8 to 46 years. Head circumference was also measured. Groups did not differ on age, sex, verbal IQ, or socioeconomic status.

RESULTS

Brain volumes were significantly larger for children with autism 12 years old and younger compared with normally developing children, when controlling for height. Brain volumes for individuals older than age 12 did not differ between the autism and control groups. Head circumference was increased in both younger and older groups of subjects with autism, suggesting that those subjects older than age 12 had increased brain volumes as children.

CONCLUSIONS

Brain development in autism follows an abnormal pattern, with accelerated growth in early life that results in brain enlargement in childhood. Brain volume in adolescents and adults with autism is, however, normal, and appears to be due to a slight decrease in brain volume for these individuals at the same time that normal children are experiencing a slight increase.

High motion coherence thresholds in children with autism

BACKGROUND

We assessed motion processing in a group of high functioning children with autism and a group of typically developing children, using a coherent motion detection task.

METHOD

Twenty-five children with autism (mean age 11 years, 8 months) and 22 typically developing children matched for non-verbal mental ability and chronological age were required to detect the direction of moving dots in a random dot kinematogram.

RESULTS

The group of children with autism showed significantly higher motion coherence thresholds than the typically developing children (i.e., they showed an impaired ability to detect coherent motion).

CONCLUSIONS

This finding suggests that some individuals with autism may show impairments in low-level visual processing--specifically in the magnocellular visual pathway. The findings are discussed in terms of implications for higher-level cognitive theories of autism, and the suggestion is made that more work needs to be carried out to further investigate low-level visual processing in autism.

Magnetic resonance imaging of the post-mortem autistic brain

Magnetic resonance imaging (MRI) is a valuable, noninvasive tool for understanding structural abnormalities in the brain. The M.I.N.D. Institute at UC Davis has developed a protocol utilizing MRI to investigate anatomical differences in the post-mortem brain by applying a proton density weighted imaging sequence for optimal differences in image intensity (contrast) between gray and white matter. Images of the brain obtained prior to distribution of tissue and further neuropathological examination provide a record of how the brain appeared prior to tissue processing. The virtual representation of the whole brain can also be subjected to additional analyses, such as measuring the volume of brain regions or area of the cortical surface. We describe our procedures for carrying out post-mortem MRI of the human brain.

Magnetic resonance imaging and clinical findings examined in adulthood-studies on three adults with Rett syndrome

PURPOSE

To clarify magnetic resonance imaging (MRI) findings in three adult patients with Rett syndrome who had been diagnosed with mental retardation and autism.

METHOD

Clinical and MRI findings in three adult cases with Rett syndrome were studied. Ages (in years) in three adult cases with Rett Syndrome were 46 in Case 1, 35 in Case 2 and 20 in Case 3. They were able to walk and their convulsions were well controlled.

RESULTS

MRI findings in all patients showed mild cerebral atrophy, especially in the frontal and temporal lobes and two of the cases also had mild cerebellar atrophy. One case also showed a narrowing of the brainstem and thinning of the corpus callosum.

CONCLUSIONS

These results indicate that abnormalities in MRI imaging, in cases where there is narrowing of the brainstem and thinning of the corpus callosum, may be due to congenital hypoplasia. It was also seen that cerebellar atrophy became more distinct in older cases.

Enlarged cerebellar vermis in Williams syndrome

Williams syndrome (WMS) is a rare genetic disorder characterized by relative preservations of language ability and facial processing despite deficits in overall intelligence, problem solving, and visuospatial processing. Subjects with WMS also display hypersocial behavior and excessive linguistic affect during conversations and when giving narratives. Neuroimaging studies have shown global reductions in the brain volumes of subjects with WMS compared with normal controls, but with preservations in cerebellar volume. This study examines the neuroanatomic structure of the cerebellar vermis in 20 subjects with WMS and 20 age- and gender-matched controls via high-resolution magnetic resonance imaging. The vermis was divided into lobules I-V, VI-VII, and VIII-X. Lobules VI-VII and VIII-X were both relatively enlarged in the WMS group, and after adjusting for the smaller size of the WMS brain, the posterior vermis was significantly larger in WMS (Mann-Whitney z-value=4.27; P<0.001). Given that reductions in posterior vermis size have been implicated in flattened affect and autistic features, increased vermis size in subjects with WMS may be related to the hypersociality and heightened affective expression characteristic of individuals with this genetic condition.

Brain imaging in neurogenetic conditions: realizing the potential of behavioral neurogenetics research

Behavioral neurogenetics research is a new method of scientific inquiry that focuses on investigation of neurodevelopmental dysfunction associated with specific genetic conditions. This research method provides a powerful tool for scientific inquiry into human gene-brain-behavior linkages that complements more traditional research approaches. In particular, the use of specific genetic conditions as models of common behavioral and cognitive disorders occurring in the general population can reveal insights into neurodevelopmental pathways that might otherwise be obscured or diluted when investigating more heterogeneous, behaviorally defined subject groups. In this paper, we review five genetic conditions that commonly give rise to identifiable neurodevelopmental and neuropsychiatric disability in children: fragile X syndrome, velo-cardio-facial syndrome, Williams syndrome, Turner syndrome, and Klinefelter syndrome. While emphasis is placed on describing the brain morphology associated with these conditions as revealed by neuroimaging studies, we also include information pertaining to molecular genetic, postmortem, and neurobehavioral investigations to illustrate how behavioral neurogenetics research can contribute to an improved understanding of brain disorders in childhood.