Neuroanatomy of autism

Synaptic maturation at cortical projections to the lateral amygdala in a mouse model of Rett syndrome

Rett syndrome (RTT) is a neuro-developmental disorder caused by loss of function of Mecp2 - methyl-CpG-binding protein 2 - an epigenetic factor controlling DNA transcription. In mice, removal of Mecp2 in the forebrain recapitulates most of behavioral deficits found in global Mecp2 deficient mice, including amygdala-related hyper-anxiety and lack of social interaction, pointing a role of Mecp2 in emotional learning. Yet very little is known about the establishment and maintenance of synaptic function in the adult amygdala and the role of Mecp2 in these processes. Here, we performed a longitudinal examination of synaptic properties at excitatory projections to principal cells of the lateral nucleus of the amygdala (LA) in Mecp2 mutant mice and their wild-type littermates. We first show that during animal life, Cortico-LA projections switch from a tonic to a phasic mode, whereas Thalamo-LA synapses are phasic at all ages. In parallel, we observed a specific elimination of Cortico-LA synapses and a decrease in their ability of generating presynaptic long term potentiation. In absence of Mecp2, both synaptic maturation and synaptic elimination were exaggerated albeit still specific to cortical projections. Surprisingly, associative LTP was unaffected at Mecp2 deficient synapses suggesting that synaptic maintenance rather than activity-dependent synaptic learning may be causal in RTT physiopathology. Finally, because the timing of synaptic evolution was preserved, we propose that some of the developmental effects of Mecp2 may be exerted within an endogenous program and restricted to synapses which maturate during animal life.

A common neural system mediating two different forms of social judgement

BACKGROUND

A wide range of neuropsychiatric conditions, including schizophrenia and autistic spectrum disorder (ASD), are associated with impairments in social function. Previous studies have shown that individuals with schizophrenia and ASD have deficits in making a wide range of social judgements from faces, including decisions related to threat (such as judgements of approachability) and decisions not related to physical threat (such as judgements of intelligence). We have investigated healthy control participants to see whether there is a common neural system activated during such social decisions, on the basis that deficits in this system may contribute to the impairments seen in these disorders.

METHOD

We investigated the neural basis of social decision making during judgements of approachability and intelligence from faces in 24 healthy participants using functional magnetic resonance imaging (fMRI). We used conjunction analysis to identify common brain regions activated during both tasks.

RESULTS

Activation of the amygdala, medial prefrontal cortex, inferior prefrontal cortex and cerebellum was seen during performance of both social tasks, compared to simple gender judgements from the same stimuli. Task-specific activations were present in the dorsolateral prefrontal cortex in the intelligence task and in the inferior and middle temporal cortex in the approachability task.

CONCLUSIONS

The present study identified a common network of brain regions activated during the performance of two different forms of social judgement from faces. Dysfunction of this network is likely to contribute to the broad-ranging deficits in social function seen in psychiatric disorders such as schizophrenia and ASD.

Neuroanatomical differences in brain areas implicated in perceptual and other core features of autism revealed by cortical thickness analysis and voxel-based morphometry

Autism spectrum disorder is a complex neurodevelopmental variant thought to affect 1 in 166 [Fombonne (2003): J Autism Dev Disord 33:365-382]. Individuals with autism demonstrate atypical social interaction, communication, and repetitive behaviors, but can also present enhanced abilities, particularly in auditory and visual perception and nonverbal reasoning. Structural brain differences have been reported in autism, in terms of increased total brain volume (particularly in young children with autism), and regional gray/white matter differences in both adults and children with autism, but the reports are inconsistent [Amaral et al. (2008): Trends Neurosci 31:137-145]. These inconsistencies may be due to differences in diagnostic/inclusion criteria, and age and Intelligence Quotient of participants. Here, for the first time, we used two complementary magnetic resonance imaging techniques, cortical thickness analyses, and voxel-based morphometry (VBM), to investigate the neuroanatomical differences between a homogenous group of young adults with autism of average intelligence but delayed or atypical language development (often referred to as "high-functioning autism"), relative to a closely matched group of typically developing controls. The cortical thickness and VBM techniques both revealed regional structural brain differences (mostly in terms of gray matter increases) in brain areas implicated in social cognition, communication, and repetitive behaviors, and thus in each of the core atypical features of autism. Gray matter increases were also found in auditory and visual primary and associative perceptual areas. We interpret these results as the first structural brain correlates of atypical auditory and visual perception in autism, in support of the enhanced perceptual functioning model [Mottron et al. (2006): J Autism Dev Disord 36:27-43].

White matter integrity and pictorial reasoning in high-functioning children with autism

The current study investigated the neurobiological role of white matter in visuospatial versus linguistic processing abilities in autism using diffusion tensor imaging. We examined differences in white matter integrity between high-functioning children with autism (HFA) and typically developing controls (CTRL), in relation to the groups' response times (RT) on a pictorial reasoning task under three conditions: visuospatial, V, semantic, S, and V+S, a hybrid condition allowing language use to facilitate visuospatial transformations. Diffusion-weighted images were collected from HFA and CTRL participants, matched on age and IQ, and significance maps were computed for group differences in fractional anisotropy (FA) and in RT-FA association for each condition. Typically developing children showed increased FA within frontal white matter and the superior longitudinal fasciculus (SLF). HFA showed increased FA within peripheral white matter, including the ventral temporal lobe. Additionally, RT-FA relationships in the semantic condition (S) implicated white matter near the STG and in the SLF within the temporal and frontal lobes to a greater extent in CTRL. Performance in visuospatial reasoning (V, V+S), in comparison, was related to peripheral parietal and superior precentral white matter in HFA, but to the SLF, callosal, and frontal white matter in CTRL. Our results appear to support a preferential use of linguistically-mediated pathways in reasoning by typically developing children, whereas autistic cognition may rely more on visuospatial processing networks.

Three hypotheses for developmental defects that may underlie some forms of autism spectrum disorder

PURPOSE OF REVIEW

Molecular and genetic insights into the etiology of autism spectrum disorders are now available. The field now needs to understand how these perturbations affect development and function of the brain.

RECENT FINDINGS

Herein I review the genetic mechanisms known to predispose to autism spectrum disorders, and attempt to consolidate many of these within cellular/molecular pathways that regulate development of neural systems that underlie cognition and social behaviors. In addition to the clear relationship of many susceptibility genes to activity-dependent neural responses, I propose the existence of three additional mechanisms that may contribute to autism spectrum disorders: evolutionary-driven expansion of cerebrum and cerebellar size; imbalance in the excitatory/inhibitory ratio in local and extended circuits; the hormonal effects of the male genotype.

SUMMARY

Understanding these mechanisms opens the possibility to therapeutic interventions.

Communication, interventions, and scientific advances in autism: a commentary

Autism spectrum disorders (ASD) affect approximately 1 in 150 children across the U.S., and are characterized by abnormal social actions, language difficulties, repetitive or restrictive behaviors, and special interests. ASD include autism (autistic disorder), Asperger Syndrome, and Pervasive Developmental Disorder not otherwise specified (PDD-NOS or atypical autism). High-functioning individuals may communicate with moderate-to-high language skills, although difficulties in social skills may result in communication deficits. Low-functioning individuals may have severe deficiencies in language, resulting in poor communication between the individual and others. Behavioral intervention programs have been developed for ASD, and are frequently adjusted to accommodate specific individual needs. Many of these programs are school-based and aim to support the child in the development of their skills, for use outside the classroom with family and friends. Strides are being made in understanding the factors contributing to the development of ASD, particularly the genetic contributions that may underlie these disorders. Mutant mouse models provide powerful research tools to investigate the genetic factors associated with ASD and its co-morbid disorders. In support, the BTBR T+tf/J mouse strain incorporates ASD-like social and communication deficits and high levels of repetitive behaviors. This commentary briefly reviews the reciprocal relationship between observations made during evidence-based behavioral interventions of high- versus low-functioning children with ASD and the accumulating body of research in autism, including animal studies and basic research models. This reciprocity is one of the hallmarks of the scientific method, such that research may inform behavioral treatments, and observations made during treatment may inform subsequent research.

Behavioral flexibility in a mouse model of developmental cerebellar Purkinje cell loss

Although behavioral inflexibility and Purkinje cell loss are both well established in autism, it is unknown if these phenomena are causally related. Using a mouse model, we tested the hypothesis that developmental abnormalities of the cerebellum, including Purkinje cell loss, result in behavioral inflexibility. Specifically, we made aggregation chimeras (Lc/+<-->+/+) between lurcher (Lc/+) mutant embryos and wildtype (+/+) control embryos. Lurcher mice lose 100% of their Purkinje cells postnatally, while chimeric mice lose varying numbers of Purkinje cells. We tested these mice on the acquisition and serial reversals of an operant conditional visual discrimination, a test of behavioral flexibility in rodents. During reversals 1 and 2, all groups of mice committed similar numbers of "perseverative" errors (those committed while session performance was <= 40% correct). Lurchers, however, committed a significantly greater number of "learning" errors (those committed while session performance was between 41% and 85% correct) than both controls and chimeras, and most were unable to advance past reversal 3. During reversals 3 and 4, chimeras, as a group, committed more "perseverative", but not "learning" errors than controls, although a comparison of Purkinje cell number and performance in individual mice revealed that chimeras with fewer Purkinje cells made more "learning" errors and had shorter response latencies than chimeras with more Purkinje cells. These data suggest that developmental cerebellar Purkinje cell loss may affect higher level cognitive processes which have previously been shown to be mediated by the prefrontal cortex, and are commonly deficient in autism spectrum disorders.

Autism spectrum traits in the typical population predict structure and function in the posterior superior temporal sulcus

Autism spectrum disorders (ASDs) are typically characterized by impaired social interaction and communication, narrow interests, and repetitive behaviors. The heterogeneity in the severity of these characteristics across individuals with ASD has led some researchers to suggest that these disorders form a continuum which extends into the general, or “typical,” population, and there is growing evidence that the extent to which typical adults display autistic traits, as measured using the autism-spectrum quotient (AQ), predicts performance on behavioral tasks that are impaired in ASD. Here, we show that variation in autism spectrum traits is related to cortical structure and function within the typical population. Voxel-based morphometry showed that increased AQ scores were associated with decreased white matter volume in the posterior superior temporal sulcus (pSTS), a region important in processing socially relevant stimuli and associated with structural and functional impairments in ASD. In addition, AQ was correlated with the extent of cortical deactivation of an adjacent area of pSTS during a Stroop task relative to rest, reflecting variation in resting state function. The results provide evidence that autism spectrum characteristics are reflected in neural structure and function across the typical (non-ASD) population.

GABA modulates development of cerebellar Purkinje cell dendrites under control of endocannabinoid signaling

Purkinje cells (PCs) are the sole projection neurons in the cerebellar cortex with highly arborized dendrites, on which they receive glutamatergic and GABAergic inputs. Whereas influences of glutamatergic inputs on dendritic development of PCs have been well studied, those of GABA remain elusive. Here we examined effects of GABAergic signaling on dendritogenesis of PCs in dissociated cerebellar cultures. Treatment with GABA(A) agonists such as muscimol altered Purkinje dendrites to longer and less branched morphology, while GABA(A) antagonists resulted in shorter dendrites. In contrast, neither a GABA(B) agonist nor antagonist had major effects on dendritic morphology. Simultaneous addition of a glutamatergic antagonist cocktail or the Trk receptor antagonist K252a did not block muscimol. Furthermore, blockade of endocannabinoid signaling by either AM251 or tetrahydrolipstatin resulted in longer and less branched dendrites similar to those treated with GABA(A) agonists suggesting upstream regulation by endocannabinoids. Notably, whereas Purkinje dendrites extended in random directions in the presence of muscimol, they oriented to coexisting GABAergic interneurons when treated with AM251. Taken together, our results postulate the hypothesis that GABA released from the cerebellar interneurons modulates dendritogenesis of PCs in an endocannabinoid-dependent manner in the developing cerebellar cortex.

Longitudinal magnetic resonance imaging study of cortical development through early childhood in autism

Cross-sectional magnetic resonance imaging (MRI) studies have long hypothesized that the brain in children with autism undergoes an abnormal growth trajectory that includes a period of early overgrowth; however, this has never been confirmed by a longitudinal study. We performed the first longitudinal study of brain growth in toddlers at the time symptoms of autism are becoming clinically apparent using structural MRI scans at multiple time points beginning at 1.5 years up to 5 years of age. We collected 193 scans on 41 toddlers who received a confirmed diagnosis of autistic disorder at approximately 48 months of age and 44 typically developing controls. By 2.5 years of age, both cerebral gray and white matter were significantly enlarged in toddlers with autistic disorder, with the most severe enlargement occurring in frontal, temporal, and cingulate cortices. In the longitudinal analyses, which we accounted for age and gender effect, we found that all regions (cerebral gray, cerebral white, frontal gray, temporal gray, cingulate gray, and parietal gray) except occipital gray developed at an abnormal growth rate in toddlers with autistic disorder that was mainly characterized by a quadratic age effect. Females with autistic disorder displayed a more pronounced abnormal growth profile in more brain regions than males with the disorder. Given that overgrowth clearly begins before 2 years of age, future longitudinal studies would benefit from inclusion of even younger populations as well as further characterization of genetic and other biomarkers to determine the underlying neuropathological processes causing the onset of autistic symptoms.

Gene, brain, and behavior relationships in fragile X syndrome: evidence from neuroimaging studies

Fragile X syndrome (FraX) remains the most common inherited cause of intellectual disability and provides a valuable model for studying gene-brain-behavior relationships. Over the past 15 years, structural and functional magnetic resonance imaging studies have emerged with the goal of better understanding the neural pathways contributing to the cognitive and behavioral outcomes seen in individuals with FraX. Specifically, structural MRI studies have established and begun to refine the specific topography of neuroanatomical variation associated with FraX. In addition, functional neuroimaging studies have begun to elucidate the neural underpinnings of many of the unique characteristics of FraX including difficulties with eye gaze, executive functioning, and behavioral inhibition. This review highlights studies with a focus on the relevant gene-brain-behavior connections observed in FraX. The relationship of brain regions and activation patterns to FMRP are discussed as well as the clinical cognitive and behavioral correlates of these neuroimaging findings.

Conceptual and methodological challenges for neuroimaging studies of autistic spectrum disorders

Autistic Spectrum Disorders (ASDs) are a set of complex developmental disabilities defined by impairment in social interaction and communication, as well as by restricted interests or repetitive behaviors. Neuroimaging studies have substantially advanced our understanding of the neural mechanisms that underlie the core symptoms of ASDs. Nevertheless, a number of challenges still remain in the application of neuroimaging techniques to the study of ASDs. We review three major conceptual and methodological challenges that complicate the interpretation of findings from neuroimaging studies in ASDs, and that future imaging studies should address through improved designs. These include: (1) identification and implementation of tasks that more specifically target the neural processes of interest, while avoiding the confusion that the symptoms of ASD may impose on both the performance of the task and the detection of brain activations; (2) the inconsistency that disease heterogeneity in persons with ASD can generate on research findings, particularly heterogeneity of symptoms, symptom severity, differences in IQ, total brain volume, and psychiatric comorbidity; and (3) the problems with interpretation of findings from cross-sectional studies of persons with ASD across differing age groups. Failure to address these challenges will continue to hinder our ability to distinguish findings that outline the causes of ASDs from brain processes that represent downstream or compensatory responses to the presence of the disease. Here we propose strategies to address these issues: 1) the use of simple and elementary tasks, that are easier to understand for autistic subjects; 2) the scanning of a more homogenous group of persons with ASDs, preferably at younger age; 3) the performance of longitudinal studies, that may provide more straight forward and reliable results. We believe that this would allow for a better understanding of both the central pathogenic processes and the compensatory responses in the brain of persons suffering from ASDs.

Understanding early communication signals in autism: a study of the perception of infants' cry

BACKGROUND

Previous studies have highlighted that episodes of crying of children with autistic disorder (AD) were perceived as inexplicable from their parents who could not identify causative factors. These results supported the view of AD as related to a problem of expressing and sharing emotions. Moreover, no evidence has been presented on which characteristics of a cry episode influence the adult perception. Aim of our research is to investigate how acoustical features of crying episodes modulate their perception of infants with ASD compared with infants with typical development (TD) and infants with developmental delay (DD).

METHODS

Two studies were employed. In study 1, we artificially modified structural parameters (fundamental frequency, duration of the pauses, waveform modulation) of a cry episode, and then 50 adults (parents and non-parents) were asked to judge the level of distress elicited. In study 2, acoustic analysis was applied to episodes of crying selected from retrospective home videos of 42 children with AD, TD and DD at 18 months.

RESULTS

The results showed that (1) differences in the fundamental frequency and in other structural parameters of the cry lead parents and non-parents to perceive an episode of crying as more aversive and (2) at 18 months of age, AD episodes of crying have higher fundamental frequency (f0).

CONCLUSION

Our findings offer support for the hypothesis that acoustic characteristics of episodes of crying of children with autism, especially higher fundamental frequencies, may account for mental states of uneasiness in the listener.

The neurobiology of repetitive behavior: …and men

In young, typically developing children, repetitive behavior similar to that in certain neuropsychiatric syndromes is common. Whereas this behavior is adaptive in typical development, in many disorders it forms a core component of symptoms and causes prominent impairment in the daily life of affected individuals. Understanding the neurobiological mechanisms involved repetitive behavior will improve our understanding of the pathogenesis of developmental neuropsychiatric disorders, stimulating novel approaches to these conditions. However, studies on the neurobiology of human repetitive behavior have often been limited to distinct conditions and generalization has been hindered by inconsistent terminology. In this paper, we synthesize the 'disorder-driven' literature, building on findings from fundamental animal research and translational models. These findings suggest a model for classifying repetitive behavior by its neuroanatomical correlates.

Smaller insula and inferior frontal volumes in young adults with pervasive developmental disorders

Enlarged head circumference and increased brain weight have been reported in infants with pervasive developmental disorders (PDD), and volumetric studies suggest that children with PDD have abnormally enlarged brain volumes. However, little is known about brain volume abnormalities in young adults with PDD. We explored gray matter (GM) volume in young adults with PDD. T1-weighted volumetric images were acquired with a 3-T magnetic resonance scanner from 32 males with high-functioning PDD (23.8+/-4.2 years; Full Scale Intelligence Quotient [FSIQ]=101.6+/-15.6) and 40 age-matched normal male control subjects (22.5+/-4.3 years; FSIQ=109.7+/-7.9). Regional GM volumes were compared between the two groups using voxel-based morphometry (VBM) with the Diffeomorphic Anatomical Registration using Exponentiated Lie algebra (DARTEL). Compared with the control group, the high-functioning PDD group showed significantly less GM in the right insula, the right inferior frontal gyrus, and the right inferior parietal lobule. A conservative threshold confirmed considerably smaller volumes in the right insula and inferior frontal gyrus. In these areas, negative correlations were found between Autism Spectrum Quotient scores and GM volume, although no significant correlations were found between each subject's FSIQ and GM volume. No regions showed greater GM volumes in the high-functioning PDD group. The insular cortex, which works as a relay area for multiple neurocognitive systems, may be one of the key regions underlying the complex clinical features of PDD. These smaller GM volumes in high-functioning PDD subjects may reflect the clinical features of PDD itself, rather than FSIQ.

Atypical development of white matter microstructure in adolescents with autism spectrum disorders

Diffusion tensor imaging (DTI) studies in adolescents with autism spectrum disorders (ASD) indicate aberrant neurodevelopment of frontal white matter (WM), potentially underlying abnormal social cognition and communication in ASD. Here, we further use tract-based spatial statistics (TBSS) to examine the developmental change of WM skeleton (i.e., the most compact whole-brain WM) during adolescence in ASD. This whole-brain DTI used TBSS measures fractional anisotropy (FA) and longitudinal and radial diffusivities in fifty adolescents, 25 ASD and 25 controls. Results show that adolescents with ASD versus controls had significantly reduced FA in the right posterior limb of internal capsule (increased radial diffusivity distally and reduced longitudinal diffusivity centrally). Adolescents with ASD versus controls (covarying for age and IQ) had significantly greater FA in the frontal lobe (reduced radial diffusivity), right cingulate gyrus (reduced radial diffusivity), bilateral insula (reduced radial diffusivity and increased longitudinal diffusivity), right superior temporal gyrus (reduced radial diffusivity), and bilateral middle cerebellar peduncle (reduced radial diffusivity). Notably, a significant interaction with age by group was found in the right paracentral lobule and bilateral superior frontal gyrus as indicated by an age-related FA gain in the controls whilst an age-related FA loss in the ASD. To our knowledge, this is the first study to use TBSS to examine WM in individuals with ASD. Our findings indicate that the frontal lobe exhibits abnormal WM microstructure as well as an aberrant neurodevelopment during adolescence in ASD, which support the frontal disconnectivity theory of autism.

Autism in the U.S.: social movement and legal change

The social movement surrounding autism in the U.S. has been rightly defined a ray of light in the history of social progress. The movement is inspired by a true understanding of neuro-diversity and is capable of bringing about desirable change in political discourse. At several points along the way, however, the legal reforms prompted by the autism movement have been grafted onto preexisting patterns of inequality in the allocation of welfare, education, and medical services. In a context most recently complicated by economic recession, autism-driven change bears the mark of political and legal fragmentation. Distributively, it yields ambivalent results that have not yet received systemic attention. This article aims to fill this analytical vacuum by offering, first, a synoptic view of the several legal transformations brought about or advocated for by the autism movement and, second, a framework for investigating their distributive consequences.

Predictive models of autism spectrum disorder based on brain regional cortical thickness

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a wide phenotypic range, often affecting personality and communication. Previous voxel-based morphometry (VBM) studies of ASD have identified both gray- and white-matter volume changes. However, the cerebral cortex is a 2-D sheet with a highly folded and curved geometry, which VBM cannot directly measure. Surface-based morphometry (SBM) has the advantage of being able to measure cortical surface features, such as thickness. The goals of this study were twofold: to construct diagnostic models for ASD, based on regional thickness measurements extracted from SBM, and to compare these models to diagnostic models based on volumetric morphometry. Our study included 22 subjects with ASD (mean age 9.2+/-2.1 years) and 16 volunteer controls (mean age 10.0+/-1.9 years). Using SBM, we obtained regional cortical thicknesses for 66 brain structures for each subject. In addition, we obtained volumes for the same 66 structures for these subjects. To generate diagnostic models, we employed four machine-learning techniques: support vector machines (SVMs), multilayer perceptrons (MLPs), functional trees (FTs), and logistic model trees (LMTs). We found that thickness-based diagnostic models were superior to those based on regional volumes. For thickness-based classification, LMT achieved the best classification performance, with accuracy=87%, area under the receiver operating characteristic (ROC) curve (AUC)=0.93, sensitivity=95%, and specificity=75%. For volume-based classification, LMT achieved the highest accuracy, with accuracy=74%, AUC=0.77, sensitivity=77%, and specificity=69%. The thickness-based diagnostic model generated by LMT included 7 structures. Relative to controls, children with ASD had decreased cortical thickness in the left and right pars triangularis, left medial orbitofrontal gyrus, left parahippocampal gyrus, and left frontal pole, and increased cortical thickness in the left caudal anterior cingulate and left precuneus. Overall, thickness-based classification outperformed volume-based classification across a variety of classification methods.

Regionally reduced brain volume, altered serotonin neurochemistry, and abnormal behavior in mice null for the circadian rhythm output gene Magel2

Magel2 belongs to the MAGE/necdin family of proteins, which have roles in cell cycle, differentiation, and apoptosis. The Magel2 gene is expressed in various brain regions, most notably the hypothalamus. Mice with a targeted deletion of Magel2 display hypoactivity, blunted circadian rhythm, decreased fertility, and increased adiposity. The human ortholog, MAGEL2, is one of a set of paternally expressed, imprinted genes inactivated in most cases of Prader-Willi syndrome, a complex neurodevelopmental disorder. To explore the role of Magel2, brain morphology, brain neurochemistry, and behavior were measured in Magel2-null mice. Brain volume was reduced in specific regions, particularly in the parieto-temporal lobe of the cerebral cortex, the amygdala, the hippocampus, and the nucleus accumbens, as measured by quantitative magnetic resonance imaging. Abnormal neurochemistry was detected in brain samples from adult mice, consisting of decreased serotonin and 5-hydroxyindoleacetic acid in the cortex and the hypothalamus, and decreased dopamine in the hypothalamus. Magel2-null mice displayed relatively normal motor and learning abilities, but exhibited abnormal behavior in novel environments. This study lends support to the important role of the circadian rhythm output gene Magel2 in brain structure and behavior.

Autism susceptibility candidate 2 (Auts2) encodes a nuclear protein expressed in developing brain regions implicated in autism neuropathology

Autism susceptibility candidate 2 (Auts2) is a gene associated with autism and mental retardation, whose function is unknown. Expression of Auts2 mRNA and protein were studied in the developing mouse brain by in situ hybridization, immunohistochemistry, and western blotting. Auts2 mRNA was highly expressed in the developing cerebral cortex and cerebellum, regions often affected by neuropathological changes in autism, and a few other brain regions. On embryonic day (E) 12, Auts2 mRNA was expressed in the cortical preplate, where it colocalized with Tbr1, a transcription factor specific for postmitotic projection neurons. From E16 to postnatal day 21, Auts2 was expressed most abundantly in frontal cortex, hippocampus and cerebellum, including Purkinje cells and deep nuclei. High levels of Auts2 were also detected in developing dorsal thalamus, olfactory bulb, inferior colliculus and substantia nigra. Auts2 protein showed similar regional expression patterns as the mRNA. At the cellular level, Auts2 protein was localized in the nuclei of neurons and some neuronal progenitors.

Mapping brain abnormalities in boys with autism

Children with autism spectrum disorder (ASD) exhibit characteristic cognitive and behavioral differences, but no systematic pattern of neuroanatomical differences has been consistently found. Recent neurodevelopmental models posit an abnormal early surge in subcortical white matter growth in at least some autistic children, perhaps normalizing by adulthood, but other studies report subcortical white matter deficits. To investigate the profile of these alterations in 3D, we mapped brain volumetric differences using a relatively new method, tensor-based morphometry. 3D T1-weighted brain MRIs of 24 male children with ASD (age: 9.5 years +/- 3.2 SD) and 26 age-matched healthy controls (age: 10.3 +/- 2.4 SD) were fluidly registered to match a common anatomical template. Autistic children had significantly enlarged frontal lobes (by 3.6% on the left and 5.1% on the right), and all other lobes of the brain were enlarged significantly, or at trend level. By analyzing the applied deformations statistically point-by-point, we detected significant gray matter volume deficits in bilateral parietal, left temporal and left occipital lobes (P = 0.038, corrected), trend-level cerebral white matter volume excesses, and volume deficits in the cerebellar vermis, adjacent to volume excesses in other cerebellar regions. This profile of excesses and deficits in adjacent regions may (1) indicate impaired neuronal connectivity, resulting from aberrant myelination and/or an inflammatory process, and (2) help to understand inconsistent findings of regional brain tissue excesses and deficits in autism.

Autism spectrum disorders in survivors of extreme prematurity

Recent studies in survivors of extreme prematurity point to an increased prevalence of a previously underrecognized atypical social-behavioral profile strongly suggestive of an autism spectrum disorder. Prospective studies that incorporate early autism screening and autism diagnostic testing are needed to better delineate the sensitivity and specificity of early signs of autism in ex-premature children. Advances in neonatal MRI techniques capable of quantitative structural and functional measurements will also provide important insights into the effects of prematurity itself, and prematurity-related brain injury on the genesis of autism spectrum disorders in this population. Available evidence linking prematurity and autism spectrum disorders is reviewed in this article.

Update on autism: a review of 1300 reports published in 2008

This publication, by reviewing 1300 studies published on autism in 2008, represents an update on this topic. Results include possible parental influences, maternal conditions, and studies on genes and chromosomes. Possible etiological factors involve the "extreme male brain," defects in the mirror neuron system, vaccines, underconnectivity, disorders of central coherence, and many other more specific etiologies. Assessments or tests for autism are also reviewed. Characteristics of autistic individuals include repetitive behavior, language disorders, sleep disturbances, social problems, joint attention disorders, seizures, allergic reactions, and various behavioral changes. Cognitive changes involve IQ, reasoning, and verbal and language disorders. The savant syndrome is a fascinating phenomenon, at times seen in autistic individuals. Neurophysiological and neuroanatomical changes are also reviewed, as are comorbid conditions. Finally, treatment involves various medications including risperidone, ziprasidone, and antipsychotic drugs, as well as different procedures such as magnetic stimulation, acupuncture, and hyperbaric oxygen therapy. As mentioned in the 2007 survey, nearly every conceivable problem that a child can have may be found in these unfortunate children and nearly every conceivable etiology has been mentioned to account for this serious disorder.

A meta-analysis of the corpus callosum in autism

BACKGROUND

Previous magnetic resonance imaging (MRI) studies have reported reductions in corpus callosum (CC) total area and CC regions in individuals with autism. However, studies have differed concerning the magnitude and/or region contributing to CC reductions. The present study determined the significance and magnitude of reductions in CC total and regional area measures in autism.

METHOD

PubMed and PsycINFO databases were searched to identify MRI studies examining corpus callosum area in autism. Ten studies contributed data from 253 patients with autism (mean age = 14.58, SD = 6.00) and 250 healthy control subjects (mean age = 14.47, SD = 5.31). Of these 10 studies, 8 reported area measurements for corpus callosum regions (anterior, mid/body, and posterior), and 6 reported area for Witelson subdivisions. Meta-analytic procedures were used to quantify differences in total and region CC area measurements.

RESULTS

Total CC area was reduced in autism and the magnitude of the reduction was medium (weighted mean d = .48, 95% confidence interval [CI] = .30-.66). All regions showed reductions in size with the magnitude of the effect decreasing caudally (anterior d = .49, mid/body d = .43, posterior d = .37). Witelson subdivision 3 (rostral body) showed the largest effect, indicating greatest reduction in the region containing premotor/supplementary motor neurons.

CONCLUSIONS

Corpus callosum reductions are present in autism and support the aberrant connectivity hypothesis. Future diffusion tensor imaging studies examining specific fiber tracts connecting the hemispheres are needed to identify the cortical regions most affected by CC reductions.

An autistic endophenotype results in complex immune dysfunction in healthy siblings of autistic children

BACKGROUND

Endophenotypes are simple biological aspects of a disease that can be observed in unaffected relatives at a higher rate than in the general population; an "autism endophenotype" justifies the observation that a mild reduction in ideational fluency and nonverbal generativity might be observed in healthy, unaffected relatives of children with autism. Because it is becoming apparent that autism is associated with given alleles encoding within the human leukocyte antigens region, a region of pivotal importance in immunity, we examined whether the "autism endophenotype" would extend its effects on the immune system.

METHODS

Multiple immune parameters were analyzed in autistic children (AC) (n = 20), their siblings (HSAC) (n = 15), and age- and gender-comparable healthy control subjects (HC) (n = 20) without any familiarity for autism.

RESULTS

The immune profiles of HSAC were significantly more similar to those of their autistic siblings than to what was observed in HC. Thus, in AC and HSAC compared with HC: 1) proinflammatory and interleukin-10-producing immune cells were augmented (p < .01 in both comparisons); 2) CD8(+) naïve (CD45RA(+)/CCR7+) T lymphocytes were increased (p < .0001 and p = .001); and 3) CD8(+) effector memory (CD45RA(-)/CCR7-) (p < .0001 and p = .03) as well as CD4(+) terminally differentiated (CD45RA(-)/CCR7+) (p < .05 in both comparisons) lymphocytes were diminished. Serum autoantibodies (GM1) could be detected in 10% of AC children alone.

CONCLUSIONS

Results of this pilot study indicate that a complex immune dysfunction is present both in autistic children and in their non-autistic siblings and show the presence of an "autism endophenotype" that expands its effects on immunologic functions.

Amygdala enlargement in toddlers with autism related to severity of social and communication impairments

BACKGROUND

Autism is a heterogeneous neurodevelopmental disorder of unknown etiology. The amygdala has long been a site of intense interest in the search for neuropathology in autism, given its role in emotional and social behavior. An interesting hypothesis has emerged that the amygdala undergoes an abnormal developmental trajectory with a period of early overgrowth in autism; however this finding has not been well established at young ages nor analyzed with boys and girls independently.

METHODS

We measured amygdala volumes on magnetic resonance imaging scans from 89 toddlers at 1-5 years of age (mean = 3 years). Each child returned at approximately 5 years of age for final clinical evaluation.

RESULTS

Toddlers who later received a confirmed autism diagnosis (32 boys, 9 girls) had a larger right (p < .01) and left (p < .05) amygdala compared with typically developing toddlers (28 boys, 11 girls) with and without covarying for total cerebral volume. Amygdala size in toddlers with autism spectrum disorder correlated with the severity of their social and communication impairments as measured on the Autism Diagnostic Interview and Vineland scale. Strikingly, girls differed more robustly from typical in amygdala volume, whereas boys accounted for the significant relationship of amygdala size with severity of clinical impairment.

CONCLUSIONS

This study provides evidence that the amygdala is enlarged in young children with autism; the overgrowth must begin before 3 years of age and is associated with the severity of clinical impairments. However, neuroanatomic phenotypic profiles differ between males and females, which critically affects future studies on the genetics and etiology of autism.

Inhibition by rotenone of mesencephalic neural stem-cell migration in a neurosphere assay in vitro

Parkinson disease is an age-related neurodegenerative disorder. Although the underlying pathophysiological mechanisms are incompletely understood, it has been suggested that environmental origins of sporadic Parkinson disease occur early in life. Here we examined the in vitro effects of the environmental dopaminergic toxin rotenone on neural stem cells, derived from the rat E16 mesencephalon. The neurospheres were cultured on the uncoated glass dishes. Cells emerged from the neurospheres and migrated along the radial axis. The migrating populations comprised cells that were positive for nestin, microtubule-associated proteins, and glial fibrillary acidic protein. Exposure to rotenone inhibited cell migration, decreased proliferative cells in a dose-dependent manner, and increased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells. Quantitative analysis revealed a linear function between the inhibition of migration and the rotenone concentration. Thus, we showed for the first time that rotenone exerted inhibitory effects on the migration as well as the proliferation of neural stem cells in vitro.

Autism

Autism spectrum disorders are characterised by severe deficits in socialisation, communication, and repetitive or unusual behaviours. Increases over time in the frequency of these disorders (to present rates of about 60 cases per 10,000 children) might be attributable to factors such as new administrative classifications, policy and practice changes, and increased awareness. Surveillance and screening strategies for early identification could enable early treatment and improved outcomes. Autism spectrum disorders are highly genetic and multifactorial, with many risk factors acting together. Genes that affect synaptic maturation are implicated, resulting in neurobiological theories focusing on connectivity and neural effects of gene expression. Several treatments might address core and comorbid symptoms. However, not all treatments have been adequately studied. Improved strategies for early identification with phenotypic characteristics and biological markers (eg, electrophysiological changes) might hopefully improve effectiveness of treatment. Further knowledge about early identification, neurobiology of autism, effective treatments, and the effect of this disorder on families is needed.

Sexually dimorphic features of vermis morphology in bipolar disorder

OBJECTIVES

The cerebellar vermis is increasingly implicated in bipolar disorder (BD). In this study, we investigated vermis morphology in BD using a quantitative volumetric analysis.

METHODS

Volumes for total vermis and vermis subregions V1 (lobules I-V), V2 (lobules VI-VII), and V3 (lobules VIII-X) were calculated using high-resolution structural magnetic resonance imaging obtained from 44 individuals with BD (25 females and 19 males) and 43 healthy comparison (HC) subjects (26 females and 17 males). Total vermis volumes were compared between the BD and HC groups. Potential effects of vermis subregions and clinical features were explored.

RESULTS

Total vermis volumes were significantly larger in the BD group than in the HC group (p = 0.02). There was a significant group-by-sex interaction (p = 0.02). Total vermis volumes were significantly larger in males with BD than HC males (p = 0.004); vermis volumes did not differ significantly between females with and without BD (p = 0.95). Subregion analyses showed a trend-level interaction between diagnosis and subregion (p = 0.07) in which subregion V1 volumes were significantly larger in BD participants (p = 0.001), with differences primarily driven by males (p = 0.001).

CONCLUSIONS

Our findings demonstrate increases in cerebellar vermis volumes in males with BD. These findings support the presence of structural alterations in the cerebellar vermis in BD and furthermore the influence of sex on such changes.

Cerebellum and nonmotor function

Does the cerebellum influence nonmotor behavior? Recent anatomical studies demonstrate that the output of the cerebellum targets multiple nonmotor areas in the prefrontal and posterior parietal cortex, as well as the cortical motor areas. The projections to different cortical areas originate from distinct output channels within the cerebellar nuclei. The cerebral cortical area that is the main target of each output channel is a major source of input to the channel. Thus, a closed-loop circuit represents the major architectural unit of cerebro-cerebellar interactions. The outputs of these loops provide the cerebellum with the anatomical substrate to influence the control of movement and cognition. Neuroimaging and neuropsychological data supply compelling support for this view. The range of tasks associated with cerebellar activation is remarkable and includes tasks designed to assess attention, executive control, language, working memory, learning, pain, emotion, and addiction. These data, along with the revelations about cerebro-cerebellar circuitry, provide a new framework for exploring the contribution of the cerebellum to diverse aspects of behavior.

Pathogenesis of autism: a patchwork of genetic causes

Autism spectrum disorders (ASDs) are relatively infrequent but are devastating developmental conditions characterized by marked deficiencies in social, communicative and other behavioral domains. It has been known for a substantial period of time that these disorders are genetic in nature. However, elucidating the specific mechanisms of these disorders has been difficult. A major reason for such difficulty is the recognized genetic heterogeneity of ASDs. Specifically, many genetic mechanisms related to structural variations in the genome have been reported as possible genetic causes of these disorders. This review briefly exemplifies these genetic mechanisms, presents a concise overview of the evidence for the genetic basis of ASDs and provides an appraisal of the specific structural genetic variants thought to contribute to the pathogenesis of these complex disorders.

A preliminary longitudinal magnetic resonance imaging study of brain volume and cortical thickness in autism

BACKGROUND

Autism is a developmental neurobiologic disorder associated with structural and functional abnormalities in several brain regions including the cerebral cortex. This longitudinal study examined developmental changes in brain volume and cortical thickness (CT) using magnetic resonance imaging (MRI) in children with autism.

METHODS

MRI scans and behavioral measures were obtained at baseline and after a 30-month interval in a sample of male subjects with autism (n = 18) and healthy age-, and sex-matched control subjects (n = 16) between ages 8 and 12 years at baseline.

RESULTS

No differences in brain volumes were observed between the autism and control subjects at baseline or follow-up. However, differences in total gray matter volumes were observed over time with significantly greater decreases in the autism group compared with control subjects. Differences in CT were observed over time with greater decreases in the autism group compared with control subjects in several brain regions including the frontal lobe. When accounting for multiple comparisons, differences between the two groups became nonsignificant except for changes in occipital CT. Furthermore, associations were observed between several clinical features and changes in CT with greater thinning of the cortex being correlated with more severe symptomatology.

CONCLUSIONS

Findings from this study provide preliminary evidence for age-related changes in gray matter volume and CT in children with autism that are associated with symptoms severity. Future longitudinal studies of larger sample sizes are needed to evaluate developmental changes and examine the relationships between structural abnormalities and clinical expressions of the disorder.

Investigating the predictive value of whole-brain structural MR scans in autism: a pattern classification approach

Autistic spectrum disorder (ASD) is accompanied by subtle and spatially distributed differences in brain anatomy that are difficult to detect using conventional mass-univariate methods (e.g., VBM). These require correction for multiple comparisons and hence need relatively large samples to attain sufficient statistical power. Reports of neuroanatomical differences from relatively small studies are thus highly variable. Also, VBM does not provide predictive value, limiting its diagnostic value. Here, we examined neuroanatomical networks implicated in ASD using a whole-brain classification approach employing a support vector machine (SVM) and investigated the predictive value of structural MRI scans in adults with ASD. Subsequently, results were compared between SVM and VBM. We included 44 male adults; 22 diagnosed with ASD using "gold-standard" research interviews and 22 healthy matched controls. SVM identified spatially distributed networks discriminating between ASD and controls. These included the limbic, frontal-striatal, fronto-temporal, fronto-parietal and cerebellar systems. SVM applied to gray matter scans correctly classified ASD individuals at a specificity of 86.0% and a sensitivity of 88.0%. Cases (68.0%) were correctly classified using white matter anatomy. The distance from the separating hyperplane (i.e., the test margin) was significantly related to current symptom severity. In contrast, VBM revealed few significant between-group differences at conventional levels of statistical stringency. We therefore suggest that SVM can detect subtle and spatially distributed differences in brain networks between adults with ASD and controls. Also, these differences provide significant predictive power for group membership, which is related to symptom severity.

No evidence for impaired perception of biological motion in adults with autistic spectrum disorders

A central feature of autistic spectrum disorders (ASDs) is a difficulty in identifying and reading human expressions, including those present in the moving human form. One previous study, by Blake et al. (2003), reports decreased sensitivity for perceiving biological motion in children with autism, suggesting that perceptual anomalies underlie problems in social cognition. We revisited this issue using a novel psychophysical task. 16 adults with ASDs and 16 controls were asked to detect the direction of movement of human point-light walkers which were presented in both normal and spatially scrambled forms in a background of noise. Unlike convention direction discrimination tasks, in which walkers walk 'on the spot' while facing left or right, we added translatory motion to the stimulus so that the walkers physically moved across the screen. Therefore, while a cue of coherent, translatory motion was available in both the normal and scrambled walker forms, the normal walker alone contained information about the configuration and kinematics of the human body. There was a significant effect of walker type, with reduced response times and error when the normal walker was present. Most importantly, these improvements were the same for both participant groups, suggesting that people with ASDs do not have difficulty integrating local visual information into a global percept of the moving human form. The discrepancy between these and previous findings of impaired biological motion perception in ASDs are discussed with reference to differences in the age and diagnosis of the participants, and the nature of the task.

Social skills interventions for individuals with autism: evaluation for evidence-based practices within a best evidence synthesis framework

This paper presents a best evidence synthesis of interventions to increase social behavior for individuals with autism. Sixty-six studies published in peer-reviewed journals between 2001 and July 2008 with 513 participants were included. The results are presented by the age of the individual receiving intervention and by delivery agent of intervention. The findings suggest there is much empirical evidence supporting many different treatments for the social deficits of individuals with autism. Using the criteria of evidence-based practice proposed by Reichow et al. (Journal of Autism and Developmental Disorders, 38:1311-1318, 2008), social skills groups and video modeling have accumulated the evidence necessary for the classifications of established EBP and promising EBP, respectively. Recommendations for practice and areas of future research are provided.

Syndromic autism: causes and pathogenetic pathways

BACKGROUND

Autism is a severe neurodevelopmental disorder known to have many different etiologies. In the last few years, significant progresses have been made in comprehending the causes of autism and their multiple impacts on the developing brain. This article aims to review the current understanding of the etiologies and the multiple pathogenetic pathways that are likely to lead to the autistic phenotype.

DATA SOURCES

The PubMed database was searched with the keywords "autism" and "chromosomal abnormalities", "metabolic diseases", "susceptibility loci".

RESULTS

Genetic syndromes, defined mutations, and metabolic diseases account for less than 20% of autistic patients. Alterations of the neocortical excitatory/inhibitory balance and perturbations of interneurons' development represent the most probable pathogenetic mechanisms underlying the autistic phenotype in fragile X syndrome and tuberous sclerosis complex. Chromosomal abnormalities and potential candidate genes are strongly implicated in the disruption of neural connections, brain growth and synaptic/dendritic morphology. Metabolic and mitochondrial defects may have toxic effects on the brain cells, causing neuronal loss and altered modulation of neurotransmission systems.

CONCLUSIONS

A wide variety of cytogenetic abnormalities have been recently described, particularly in the low functioning individuals with dysmorphic features. Routine metabolic screening studies should be performed in the presence of autistic regression or suggestive clinical findings. As etiologies of autism are progressively discovered, the number of individuals with idiopathic autism will progressively shrink. Studies of genetic and environmentally modulated epigenetic factors are beginning to provide some clues to clarify the complexities of autism pathogenesis. The role of the neuropediatrician will be to understand the neurological basis of autism, and to identify more homogenous subgroups with specific biologic markers.

Shared and idiosyncratic cortical activation patterns in autism revealed under continuous real-life viewing conditions

Although widespread alterations in cortical structure have been documented in individuals with autism, the functional implications of these alterations remain to be determined. Here, we adopted a novel inter-subject correlation (inter-SC) and intra-subject correlation (intra-SC) technique to quantify the reliability of the spatio-temporal responses of functional MR activity in adults with autism during free-viewing of a popular audio-visual movie. Whereas these complex stimuli evoke highly reliable shared response time courses in typical individuals, cortical activity was more variable across individuals with autism (low inter-SC). Interestingly, when we measured the responses within an autistic individual across repeated presentations of the movie, we observed a unique, idiosyncratic response time course that was reliably replicated within each individual (high intra-SC). Encouragingly, after filtering out the idiosyncratic responses from each individual time course, we were able to uncover a more typical response profile, which resembles the shared responses seen in the typical subjects. These findings indicate that, under conditions approximating real-life situations, the neural activity of individuals with autism is characterized by individualistic responses that, although reliable within an autistic individual, are both highly variable across autistic individuals and different from the responses observed within the typical subjects. These idiosyncratic responses may underlie the atypical behaviors observed in autism. At the same time, we are encouraged by the presence of the more typical activation pattern lurking beneath these idiosyncratic fluctuations. Taken together, these findings may pave the way to future research aimed at characterizing the idiosyncratic response profiles, which, in turn, might contribute to a better understanding of the heterogeneity of the autism spectrum and its diagnosis.

Mechanistic biomarkers for autism treatment

OBJECTIVE

Autism is a syndrome with a number of etiologies with differing mechanisms that lead to abnormal development. This review highlights the need to identify autism subgroups as they each might require unique approaches for prevention or treatment.

METHODS

Targeting treatments to specific mechanisms and utilizing biomarkers can more rapidly advance our understanding of how to classify and treat autism subgroups based on translational mechanisms. We illustrate this approach using mechanisms that may influence the course of autism and provide rationale for selected biomarkers that could guide treatments targeted anywhere from DNA to symptom expression.

CONCLUSIONS

The use of potential biomarkers that point to specific mechanisms of disordered neurodevelopment will help identify meaningful subtypes of autism and will help tailor treatment or prevention strategies for each mechanism rather than solely to a symptom category.

Fibroblast growth factor signaling in development of the cerebral cortex

Despite substantial and exciting recent progress in our understanding of developmental processes in the cerebral cortex, there is still much to be learned about the molecular and cellular mechanisms that account for formation of the cortical structures, and in turn, how the regulation of these mechanisms is linked to cortical functions and behaviors in animals and humans. Fibroblast growth factors (FGFs) are a classic family of growth factors that are important in neural development and whose structures and signaling have been well-studied molecularly and biochemically. Recent advances have revealed their diverse but specific functions in patterning and neurogenesis during cortical development, as evidenced by multiple experimental approaches using in vivo models. Importantly, changes in FGF signaling during development have been shown to influence structure and function of the cerebral cortex as well as animal behavior, and have been implicated in disorders of nervous system function and intellectual development in humans. For example, disturbance of FGF pathways during development has been implicated in the pathogenesis of autism spectrum disorders. Experimental models with altered cortical structure due to perturbations of FGF signaling present a unique opportunity whereby molecular and cellular mechanisms that underlie cortical function and animal behavior can be directly studied and linked to each other.

A synaptic trek to autism

Autism spectrum disorders (ASD) are diagnosed on the basis of three behavioral features namely deficits in social communication, absence or delay in language, and stereotypy. The susceptibility genes to ASD remain largely unknown, but two major pathways are emerging. Mutations in TSC1/TSC2, NF1, or PTEN activate the mTOR/PI3K pathway and lead to syndromic ASD with tuberous sclerosis, neurofibromatosis, or macrocephaly. Mutations in NLGN3/4, SHANK3, or NRXN1 alter synaptic function and lead to mental retardation, typical autism, or Asperger syndrome. The mTOR/PI3K pathway is associated with abnormal cellular/synaptic growth rate, whereas the NRXN-NLGN-SHANK pathway is associated with synaptogenesis and imbalance between excitatory and inhibitory currents. Taken together, these data strongly suggest that abnormal synaptic homeostasis represent a risk factor to ASD.

Using zebrafish to assess the impact of drugs on neural development and function

BACKGROUND: Zebrafish is becoming an increasingly attractive model organism for understanding biology and developing therapeutics, because as a vertebrate, it shares considerable similarity with mammals in both genetic compositions and tissue/organ structures, and yet remains accessible to high throughput phenotype-based genetic and small molecule compound screening. OBJECTIVE/METHOD: The focus of this review is on the nervous system, which is arguably the most complex organ and known to be afflicted by more than six hundred disorders in humans. I discuss the past, present, and future of using zebrafish to assess the impact of small molecule drugs on neural development and function, in light of understanding and treating neurodevelopmental disorders such as autism, neurodegenerative disorders including Alzheimer's, Parkinson's, and Hungtington's disease, and neural system dysfunctions such as anxiety/depression and addiction. CONCLUSION: These studies hold promise to reveal fundamental mechanisms governing nervous system development and function, and to facilitate small molecule drug discovery for the many types of neurological disorders.

The pathophysiology of restricted repetitive behavior

Restricted, repetitive behaviors (RRBs) are heterogeneous ranging from stereotypic body movements to rituals to restricted interests. RRBs are most strongly associated with autism but occur in a number of other clinical disorders as well as in typical development. There does not seem to be a category of RRB that is unique or specific to autism and RRB does not seem to be robustly correlated with specific cognitive, sensory or motor abnormalities in autism. Despite its clinical significance, little is known about the pathophysiology of RRB. Both clinical and animal models studies link repetitive behaviors to genetic mutations and a number of specific genetic syndromes have RRBs as part of the clinical phenotype. Genetic risk factors may interact with experiential factors resulting in the extremes in repetitive behavior phenotypic expression that characterize autism. Few studies of individuals with autism have correlated MRI findings and RRBs and no attempt has been made to associate RRB and post-mortem tissue findings. Available clinical and animal models data indicate functional and structural alterations in cortical-basal ganglia circuitry in the expression of RRB, however. Our own studies point to reduced activity of the indirect basal ganglia pathway being associated with high levels of repetitive behavior in an animal model. These findings, if generalizable, suggest specific therapeutic targets. These, and perhaps other, perturbations to cortical basal ganglia circuitry are mediated by specific molecular mechanisms (e.g., altered gene expression) that result in long-term, experience-dependent neuroadaptations that initiate and maintain repetitive behavior. A great deal more research is needed to uncover such mechanisms. Work in areas such as substance abuse, OCD, Tourette syndrome, Parkinson's disease, and dementias promise to provide findings critical for identifying neurobiological mechanisms relevant to RRB in autism. Moreover, basic research in areas such as birdsong, habit formation, and procedural learning may provide additional, much needed clues. Understanding the pathophysioloy of repetitive behavior will be critical to identifying novel therapeutic targets and strategies for individuals with autism.

A functional polymorphism of the brain derived neurotrophic factor gene and cortical anatomy in autism spectrum disorder

Autism Spectrum Disorder (ASD) is associated with both (i) post-mortem and neuroimaging evidence of abnormal cortical development, and (ii) altered signalling in Brain Derived Neurotrophic Factor (BDNF) pathways - which regulate neuroproliferative and neuroplastic processes. In healthy controls genotype at a single nucleotide polymorphism that alters BDNF signalling (Val66met) has been related to regional cortical volume. It is not known however if this influence on brain development is intact in ASD. Therefore we compared the relationship between genotype and cortical anatomy (as measured using in vivo Magnetic Resonance Imaging) in 41 people with ASD and 30 healthy controls. We measured cortical volume, and its two sole determinants - cortical thickness and surface area - which reflect differing neurodevelopmental processes. We found “Group-by-Genotype” interactions for cortical volume in medial (caudal anterior cingulate, posterior cingulate) and lateral (rostral middle, lateral orbitofrontal, pars orbitalis and pars triangularis) frontal cortices. Furthermore, within (only) these regions “Group-by-Genotype” interactions were also found for surface area. No effects were found for cortical thickness in any region. Our preliminary findings suggest that people with ASD have differences from controls in the relationship between BDNF val66met genotype and regional (especially frontal) cortical volume and surface area, but not cortical thickness. Therefore alterations in the relationship between BDNF val66met genotype and surface area in ASD may drive the findings for volume. If correct, this suggests ASD is associated with a distorted relationship between BDNF val66met genotype and the determinants of regional cortical surface area – gyrification and/or sulcal positioning.