Brain metabolism in autism. Resting cerebral glucose utilization rates as measured with positron emission tomography

Resting-State Functional MRI and PET Imaging as Noninvasive Tools to Study (Ab)Normal Neurodevelopment in Humans and Rodents

Neurodevelopmental disorders (NDDs) are a group of complex neurologic and psychiatric disorders. Functional and molecular imaging techniques, such as resting-state functional magnetic resonance imaging (rs-fMRI) and positron emission tomography (PET), can be used to measure network activity noninvasively and longitudinally during maturation in both humans and rodent models. Here, we review the current knowledge on rs-fMRI and PET biomarkers in the study of normal and abnormal neurodevelopment, including intellectual disability (ID; with/without epilepsy), autism spectrum disorder (ASD), and attention deficit hyperactivity disorder (ADHD), in humans and rodent models from birth until adulthood, and evaluate the cross-species translational value of the imaging biomarkers. To date, only a few isolated studies have used rs-fMRI or PET to study (abnormal) neurodevelopment in rodents during infancy, the critical period of neurodevelopment. Further work to explore the feasibility of performing functional imaging studies in infant rodent models is essential, as rs-fMRI and PET imaging in transgenic rodent models of NDDs are powerful techniques for studying disease pathogenesis, developing noninvasive preclinical imaging biomarkers of neurodevelopmental dysfunction, and evaluating treatment-response in disease-specific models.

Neuroimaging genetics approaches to identify new biomarkers for the early diagnosis of autism spectrum disorder

Autism-spectrum disorders (ASDs) are developmental disabilities that manifest in early childhood and are characterized by qualitative abnormalities in social behaviors, communication skills, and restrictive or repetitive behaviors. To explore the neurobiological mechanisms in ASD, extensive research has been done to identify potential diagnostic biomarkers through a neuroimaging genetics approach. Neuroimaging genetics helps to identify ASD-risk genes that contribute to structural and functional variations in brain circuitry and validate biological changes by elucidating the mechanisms and pathways that confer genetic risk. Integrating artificial intelligence models with neuroimaging data lays the groundwork for accurate diagnosis and facilitates the identification of early diagnostic biomarkers for ASD. This review discusses the significance of neuroimaging genetics approaches to gaining a better understanding of the perturbed neurochemical system and molecular pathways in ASD and how these approaches can detect structural, functional, and metabolic changes and lead to the discovery of novel biomarkers for the early diagnosis of ASD.

Resting-state coupling between HbO and Hb measured by fNIRS in autism spectrum disorder

To distinguish between children with autism spectrum disorder (ASD) and typically developing (TD) children, we have uncovered a new discriminative feature, hemoglobin coupling. Functional near-infrared spectroscopy (fNIRS) was used to record resting-state hemodynamic fluctuations in the bilateral temporal lobes in 25 children with ASD and 22 TD children, in which the coupling between low frequency oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (Hb) fluctuations was evaluated by Pearson correlation coefficient. The results showed significantly weak coupling in children with ASD in both the left and right, and throughout the whole temporal cortex. To explain this observation, a simulation study was performed using a balloon model, in which we found four related parameters could impact the coupling. This study suggested that hemoglobin coupling might be applied as a new cerebral hemodynamic characteristic for ASD screening or diagnostics.

KMT2E Haploinsufficiency Manifests Autism-Like Behaviors and Amygdala Neuronal Development Dysfunction in Mice

Autism spectrum disorders (ASD) are highly heterogeneous neurodevelopmental disorders characterized by impaired social interaction skills. Whole exome sequencing has identified loss-of-function mutations in lysine methyltransferase 2E (KMT2E, also named MLL5) in ASD patients and it is listed as an ASD high-risk gene in humans. However, experimental evidence of KMT2E in association with ASD-like manifestations or neuronal function is still missing. Relying on KMT2E^+/- mice, through animal behavior analyses, positron emission tomography (PET) imaging, and neuronal morphological analyses, we explored the role of KMT2E haploinsufficiency in ASD-like symptoms. Behavioral results revealed that KMT2E haploinsufficiency was sufficient to produce social deficit, accompanied by anxiety in mice. Whole-brain ¹⁸F-FDG-PET analysis identified that relative amygdala glycometabolism was selectively decreased in KMT2E^+/- mice compared to wild-type mice. The numbers and soma sizes of amygdala neurons in KMT2E^+/- mice were prominently increased. Additionally, KMT2E mRNA levels in human amygdala were significantly decreased after birth during brain development. Our findings support a causative role of KMT2E in ASD development and suggest that amygdala neuronal development abnormality is likely a major underlying mechanism.

Diversifying autism neuroimaging research: An arterial spin labeling review

Cognition and brain homeostasis depends on cerebral blood flow to secure adequate oxygen and nutrient distribution to the brain tissue. Altered cerebral blood flow has previously been reported in individuals diagnosed with autism spectrum condition in comparison to non-autistics. This phenomenon might suggest cerebral blood flow as a potential biomarker for autism spectrum condition. Major technological advancement enables the non-invasive and quantitative measurement of cerebral blood flow via arterial spin labeling magnetic resonance imaging. However, most neuroimaging studies in autistic individuals exploit the indirect blood oxygen level dependent functional magnetic resonance imaging signal instead. Therefore, this review examines the use of arterial spin labeling to further investigate the neurobiology of the autism spectrum condition. Followed by a comparison of results from molecular imaging and arterial spin labeling studies and a discussion concerning the future direction and potential of arterial spin labeling in this context. We found that arterial spin labeling study results are consistent with those of molecular imaging, especially after considering the effect of age and sex. Arterial spin labeling has numerous application possibilities besides the quantification of cerebral blood flow, including assessment of functional connectivity and arterial transit time. Therefore, we encourage researchers to explore and consider the application of arterial spin labeling for future scientific studies in the quest to better understand the neurobiology of autism spectrum condition.

Lay abstract

Brain function and health depend on cerebral blood flow to secure the necessary delivery of oxygen and nutrients to the brain tissue. However, cerebral blood flow appears to be altered in autistic compared to non-autistic individuals, potentially suggesting this difference to be a cause and potential identification point of autism. Recent technological development enables precise and non-invasive measurement of cerebral blood flow via the magnetic resonance imaging method referred to as arterial spin labeling. However, most neuroimaging studies still prefer using the physiologically indirect measure derived from functional magnetic resonance imaging. Therefore, this review examines the use of arterial spin labeling to further investigate the neurobiology of autism. Furthermore, the review includes a comparison of results from molecular imaging and arterial spin labeling followed by a discussion concerning the future direction and potential of arterial spin labeling. We found that arterial spin labeling study results are consistent with those of molecular imaging, especially after considering the effect of age and sex. In addition, arterial spin labeling has numerous application possibilities besides the quantification of cerebral blood flow. Therefore, we encourage researchers to explore and consider the application of arterial spin labeling for future scientific studies in the quest to better understand the neurobiology of autism.

Positron Emission Tomography in the Neuroimaging of Autism Spectrum Disorder: A Review

Autism spectrum disorder (ASD) is a basket term for neurodevelopmental disorders characterized by marked impairments in social interactions, repetitive and stereotypical behaviors, and restricted interests and activities. Subtypes include (A) disorders with known genetic abnormalities including fragile X syndrome, Rett syndrome, and tuberous sclerosis and (B) idiopathic ASD, conditions with unknown etiologies. Positron emission tomography (PET) is a molecular imaging technology that can be utilized in vivo for dynamic and quantitative research, and is a valuable tool for exploring pathophysiological mechanisms, evaluating therapeutic efficacy, and accelerating drug development in ASD. Recently, several imaging studies on ASD have been published and physiological changes during ASD progression was disclosed by PET. This paper reviews the specific radioligands for PET imaging of critical biomarkers in ASD, and summarizes and discusses the similar and different discoveries in outcomes of previous studies. It is of great importance to identify general physiological changes in cerebral glucose metabolism, cerebral blood flow perfusion, abnormalities in neurotransmitter systems, and inflammation in the central nervous system in ASD, which may provide excellent points for further ASD research.

Neurobiological substrates underlying corpus callosum hypoconnectivity and brain metabolic patterns in the valproic acid rat model of autism spectrum disorder

Atypical connectivity between brain regions and altered structure of the corpus callosum (CC) in imaging studies supports the long-distance hypoconnectivity hypothesis proposed for autism spectrum disorder (ASD). The aim of this study was to unveil the CC ultrastructural and cellular changes employing the valproic acid (VPA) rat model of ASD. Male Wistar rats were exposed to VPA (450 mg/kg i.p.) or saline (control) during gestation (embryonic day 10.5), and maturation, exploration, and social behavior were subsequently tested. Myelin content, ultrastructure, and oligodendroglial lineage were studied in the CC at post-natal days 15 (infant) and 36 (juvenile). As a functional outcome, brain metabolic activity was determined by positron emission tomography. Concomitantly with behavioral deficits in juvenile VPA rats, the CC showed reduced myelin basic protein, conserved total number of axons, reduced percentage of myelinated axons, and aberrant and less compact arrangements of myelin sheath ultrastructure. Mature oligodendrocytes decreased and oligodendrocyte precursors increased in the absence of astrogliosis or microgliosis. In medial prefrontal and somatosensory cortices of juvenile VPA rats, myelin ultrastructure and oligodendroglial lineage were preserved. VPA animals exhibited global brain hypometabolism and local hypermetabolism in brain regions relevant for ASD. In turn, the CC of infant VPA rats showed reduced myelin content but preserved oligodendroglial lineage. Our findings indicate that CC hypomyelination is established during infancy and prior to oligodendroglial pattern alterations, which suggests that axon-oligodendroglia communication could be compromised in VPA animals. Thus, CC hypomyelination may underlie white matter alterations and contribute to atypical patterns of connectivity and metabolism found in ASD.

Prevalence and Characteristics of Sensory Processing Abnormalities and its Correlation with FDG-PET Findings in Children with Autism

OBJECTIVE

To study the prevalence and characteristics of Sensory processing abnormalities (SPAs) in children with autism and to study if there is any correlation between sensory processing abnormalities with FDG-PET findings in children with severe autism.

METHODS

One hundred children, aged 3-12 y, diagnosed as Autistic spectrum disorder; ASD (DSM-V) and 100 age and sex matched controls were studied. SPAs were detected using Short sensory profile (SSP) questionnaire. Children with progressive neurological diseases, active epilepsy and structural brain abnormalities were excluded. On Childhood Autism rating scale, 30 children had severe and 70 had mild-moderate autism. The pattern of sensory processing abnormalities in children with severe ASD was compared with mild-moderate ASD. FDG-PET scan was done in children with severe autism and correlated with SPAs.

RESULTS

All children with severe autism had sensory processing abnormalities as compared to only 40% children with mild-moderate autism. Underresponsiveness/seeking-sensation was affected in all children with severe ASD and 82% had movement sensitivity. In children with mild-moderate ASD, 45% had auditory filtering, 30% had movement sensitivity and 27% had underresponsiveness/seeking-sensation. FDG-PET was abnormal in 17% of children with severe autism. Diffuse cerebral/ temporal lobe hypometabolism, increased bilateral frontal lobe uptake and moderate reduction in parietal lobe (Lt > Rt) was observed.

CONCLUSIONS

All patients with severe autism had SPAs. However, they did not correlate with FDG-PET findings.

Hyperperfusion of Frontal White and Subcortical Gray Matter in Autism Spectrum Disorder

BACKGROUND

Our aim was to assess resting cerebral blood flow (rCBF) in children and adults with autism spectrum disorder (ASD).

METHODS

We acquired pulsed arterial spin labeling magnetic resonance imaging data in 44 generally high-functioning participants with ASD simplex and 66 typically developing control subjects with comparable mean full-scale IQs. We compared rCBF values voxelwise across diagnostic groups and assessed correlations with symptom scores. We also assessed the moderating influences of participant age, sex, and IQ on our findings and the correlations of rCBF with N-acetylaspartate metabolite levels.

RESULTS

We detected significantly higher rCBF values throughout frontal white matter and subcortical gray matter in participants with ASD. rCBF correlated positively with socialization deficits in participants with ASD in regions where hyperperfusion was greatest. rCBF declined with increasing IQ in the typically developing group, a correlation that was absent in participants with ASD, whose rCBF values were elevated across all IQ levels. rCBF in the ASD group correlated inversely with N-acetylaspartate metabolite levels throughout the frontal white matter, with greater rCBF accompanying lower and increasingly abnormal N-acetylaspartate levels relative to those of typically developing control subjects.

CONCLUSIONS

These findings taken together suggest the presence of altered metabolism, likely of mitochondrial origin, and dysfunctional maintenance processes that support axonal functioning in ASD. These disturbances in turn likely reduce neural efficiency for cognitive and social functioning and trigger compensatory responses from supporting glial cells, which subsequently increase rCBF to affected white matter. These findings, if confirmed, suggest cellular and molecular targets for novel therapeutics that address axonal pathology and bolster glial compensatory responses in ASD.

Impact of Global Mean Normalization on Regional Glucose Metabolism in the Human Brain

Because the human brain consumes a disproportionate fraction of the resting body's energy, positron emission tomography (PET) measurements of absolute glucose metabolism (CMR_glc) can serve as disease biomarkers. Global mean normalization (GMN) of PET data reveals disease-based differences from healthy individuals as fractional changes across regions relative to a global mean. To assess the impact of GMN applied to metabolic data, we compared CMR_glc with and without GMN in healthy awake volunteers with eyes closed (i.e., control) against specific physiological/clinical states, including healthy/awake with eyes open, healthy/awake but congenitally blind, healthy/sedated with anesthetics, and patients with disorders of consciousness. Without GMN, global CMR_glc alterations compared to control were detected in all conditions except in congenitally blind where regional CMR_glc variations were detected in the visual cortex. However, GMN introduced regional and bidirectional CMR_glc changes at smaller fractions of the quantitative delocalized changes. While global information was lost with GMN, the quantitative approach (i.e., a validated method for quantitative baseline metabolic activity without GMN) not only preserved global CMR_glc alterations induced by opening eyes, sedation, and varying consciousness but also detected regional CMR_glc variations in the congenitally blind. These results caution the use of GMN upon PET-measured CMR_glc data in health and disease.

Molecular imaging of autism spectrum disorder

Autism spectrum disorder (ASD) is a condition with onset in early childhood characterized by marked deficits in interpersonal interactions and communication and by a restricted and repetitive range of interests and activities. This review points out key recent findings utilizing molecular imaging including magnetic resonance spectroscopy (MRS) and nuclear neuroimaging techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). MRS indicates an excitatory/inhibitory imbalance in high-functioning autism. Dysfunction of neurotransmitter and glucose metabolism has been demonstrated by PET and SPECT. Levels of serotonin synthesis in typically developing children are approximately twice those of adults; after the age of 5 years, levels decrease to those of adults. In contrast, levels of serotonin synthesis of children with ASD increase between ages 2 and 15 to 1.5-times adult values. The dopamine transporter is increased in the orbitofrontal cortex of men with ASD. The serotonin transporter is reduced in the brains of children, adolescents, and adults with ASD. Reduced serotonin receptors in the thalamus of adults with ASD are associated with communication difficulties. Glucose metabolism is reduced in the brains of people with ASD. Molecular imaging will provide the preliminary data for promising therapeutic interventions.

Changes in brain metabolic connectivity underlie autistic-like social deficits in a rat model of autism spectrum disorder

The neurobiological basis of social dysfunction and the high male prevalence in autism spectrum disorder (ASD) remain poorly understood. Although network alterations presumably underlie the development of autistic-like behaviors, a clear pattern of connectivity differences specific to ASD has not yet emerged. Because the heterogeneous nature of ASD hinders investigations in human subjects, we explored brain connectivity in an etiologically homogenous rat model of ASD induced by exposure to valproic acid (VPA) in utero. We performed partial correlation analysis of cross-sectional resting-state ¹⁸F-fluorodeoxyglucose positron emission tomography scans from VPA-exposed and control rats to estimate metabolic connectivity and conducted canonical correlation analysis of metabolic activity and behavior scores. VPA-treated rats exhibited impairments in social behaviors, and this difference was more pronounced in male than female rats. Similarly, current analyses revealed sex-specific changes in network connectivity and identified distinct alterations in the distributed metabolic activity patterns associated with autistic-like social deficits. Specifically, diminished activity in the salience network and enhanced activity in a cortico-cerebellar circuit correlated with the severity of social behavioral deficits. Such metabolic connectivity features may represent neurobiological substrates of autistic-like behavior, particularly in males, and may serve as a pathognomonic sign in the VPA rat model of ASD.

Connecting the dots: Overlaps between autism and cancer suggest possible common mechanisms regarding signaling pathways related to metabolic alterations

Common features between autism spectrum disorders (ASDs) and cancer have been discerned using methodologies from a number of disciplines, including genetics, bioinformatics and epidemiological studies. To understand such apparent overlaps between these two conditions and the mechanisms that may underlie these linkages, it is important to look at their multi-level systems context. Here we discuss ASDs and cancer linkages across levels ranging from genes to pathways and systems, as well as from the vantage points of mechanism and of clinical and epidemiological studies. Review of existing findings yielded evidence that ASDs and cancer overlap extensively in signal transduction pathways that are involved in metabolic processes. We hypothesize that further studies focusing on illuminating the relationships between ASDs and cancer, specifically with regard to signaling pathways that regulate metabolic activities, could help shed new insight on these conditions and develop treatment strategies that, by targeting underlying mechanisms, may be more efficient and effective for both conditions.

Regional Cerebral Glucose Metabolism and its Association with Phenotype and Cognitive Functioning in Patients with Autism

INTRODUCTION

In spite of three decades of neuroimaging, we are unable to find consistent and coherent anatomical or pathophysiological basis for autism as changes are subtle and there are no studies from India.

AIM

To study the regional cerebral glucose metabolism in children with autism using positron emission tomography (PET) scan and to study the behavior and cognitive functioning among them.

MATERIALS AND METHODS

Ten subjects (8-19 years) meeting Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria for autism were evaluated on Childhood Autism Rating Scale (CARS), trail making test (TMT) A and B, Wisconsin card sorting test, Raven's progressive matrices, and PET scan. A control group of 15 matched subjects without any brain pathology or neurological disorder was similarly studied.

RESULTS

Four out of the ten patients with autism had abnormal PET scan findings, and in contrast, none of the patients in the control group had abnormal PET scan. Of the four patients with abnormality in the PET scan, two patients had findings suggestive of hypometabolism in cerebellum bilaterally; one patient showed bilateral hypometabolism in anterior temporal cortices and cerebellum, and the fourth patient had hypermetabolism in the bilateral frontal cortices and medial occipital cortices. Subjects with autism performed poorly on neuropsychological testing. Patients with abnormal PET scan findings had significantly higher scores on the "body use" domain of CARS indicating more stereotypy.

CONCLUSION

Findings of this study support the view of altered brain functioning in subjects with autism.

Nucleus accumbens deep brain stimulation for a patient with self-injurious behavior and autism spectrum disorder: functional and structural changes of the brain: report of a case and review of literature

The aim of this report was to investigate the clinical outcome of deep brain stimulation (DBS) for autism spectrum disorder (ASD) and the functional and structural changes in the brain after DBS. We present a 14-year-old boy with ASD and self-injurious behavior (SIB) refractory with medical and behavioral therapy. He was treated by bilateral nucleus accumbens (NAc) DBS. Remarkable clinical improvement was observed following NAc DBS. Brain fluorodeoxyglucose-positron emission tomography (FDG-PET) and magnetic resonance imaging (MRI) volumetric studies revealed that the metabolism in the prefrontal and the frontal cortex as well as the occipital cortex was markedly decreased in association with the decreased cortical volumes in those areas 2 years after NAc DBS. The therapeutic potential of NAc DBS is suggested for the clinical improvement of patients with ASD and SIB with structural and functional changes after DBS.

Predicting symptom severity in autism spectrum disorder based on cortical thickness measures in agglomerative data

Machine learning approaches have been widely used for the identification of neuropathology from neuroimaging data. However, these approaches require large samples and suffer from the challenges associated with multi-site, multi-protocol data. We propose a novel approach to address these challenges, and demonstrate its usefulness with the Autism Brain Imaging Data Exchange (ABIDE) database. We predict symptom severity based on cortical thickness measurements from 156 individuals with autism spectrum disorder (ASD) from four different sites. The proposed approach consists of two main stages: a domain adaptation stage using partial least squares regression to maximize the consistency of imaging data across sites; and a learning stage combining support vector regression for regional prediction of severity with elastic-net penalized linear regression for integrating regional predictions into a whole-brain severity prediction. The proposed method performed markedly better than simpler alternatives, better with multi-site than single-site data, and resulted in a considerably higher cross-validated correlation score than has previously been reported in the literature for multi-site data. This demonstration of the utility of the proposed approach for detecting structural brain abnormalities in ASD from the multi-site, multi-protocol ABIDE dataset indicates the potential of designing machine learning methods to meet the challenges of agglomerative data.

The Neurobiology of Infantile Autism

Early infantile autism is the most severe of a group of neurodevelopmental syndromes called the pervasive developmental disorders. The clinical features of autism vary greatly, but, by definition, include deficits in social relatedness, communication, and interests or routines. The onset of autistic signs and behaviors typ ically occurs in infancy, and the syndrome is usually fully present by the fourth year. The presence of mental retardation affects the clinical picture greatly. Severely autistic children may be retarded and mute and are often preoccupied with repetitive activities; they often exhibit motor stereotypes, such as rocking or hand flapping. They can be profoundly withdrawn and may show extreme aversion to social or physical contact. More mildly affected children may have normal or even superior intelligence, with well-developed language skills. Their deficits in social relatedness and preoccupation with rituals and routines may set them apart as very odd, but not necessarily as autistic. Autism occurs in 1 of 2000 live births; boys outnumber girls about 3 or 4:1. Although there are no localizing neurological signs in autism, mild or "soft" neurological signs are common and grand mal seizures are frequently present after puberty (Lotspeich LJ, Ciaranello RD. The neurobiology and genetics of infantile autism. In: Bradley R, editor. International reviews of neurobiology. San Diego: Academic Press 1993:87-129). The Neuroscientist 1:361-367, 1995

Uniform distributions of glucose oxidation and oxygen extraction in gray matter of normal human brain: No evidence of regional differences of aerobic glycolysis

Regionally variable rates of aerobic glycolysis in brain networks identified by resting-state functional magnetic resonance imaging (R-fMRI) imply regionally variable adenosine triphosphate (ATP) regeneration. When regional glucose utilization is not matched to oxygen delivery, affected regions have correspondingly variable rates of ATP and lactate production. We tested the extent to which aerobic glycolysis and oxidative phosphorylation power R-fMRI networks by measuring quantitative differences between the oxygen to glucose index (OGI) and the oxygen extraction fraction (OEF) as measured by positron emission tomography (PET) in normal human brain (resting awake, eyes closed). Regionally uniform and correlated OEF and OGI estimates prevailed, with network values that matched the gray matter means, regardless of size, location, and origin. The spatial agreement between oxygen delivery (OEF≈0.4) and glucose oxidation (OGI ≈ 5.3) suggests that no specific regions have preferentially high aerobic glycolysis and low oxidative phosphorylation rates, with globally optimal maximum ATP turnover rates (VATP ≈ 9.4 µmol/g/min), in good agreement with (31)P and (13)C magnetic resonance spectroscopy measurements. These results imply that the intrinsic network activity in healthy human brain powers the entire gray matter with ubiquitously high rates of glucose oxidation. Reports of departures from normal brain-wide homogeny of oxygen extraction fraction and oxygen to glucose index may be due to normalization artefacts from relative PET measurements.

Persistent Angiogenesis in the Autism Brain: An Immunocytochemical Study of Postmortem Cortex, Brainstem and Cerebellum

In the current work, we conducted an immunocytochemical search for markers of ongoing neurogenesis (e.g. nestin) in auditory cortex from postmortem sections of autism spectrum disorder (ASD) and age-matched control donors. We found nestin labeling in cells of the vascular system, indicating blood vessels plasticity. Evidence of angiogenesis was seen throughout superior temporal cortex (primary auditory cortex), fusiform cortex (face recognition center), pons/midbrain and cerebellum in postmortem brains from ASD patients but not control brains. We found significant increases in both nestin and CD34, which are markers of angiogenesis localized to pericyte cells and endothelial cells, respectively. This labeling profile is indicative of splitting (intussusceptive), rather than sprouting, angiogenesis indicating the blood vessels are in constant flux rather than continually expanding.

Neurodevelopmental sequelae associated with gray and white matter changes and their cellular basis: A comparison between Autism Spectrum Disorder, ADHD and dyslexia

Many psychiatric diseases, such as major depression and schizophrenia, are accompanied by patterns of gray matter and white matter changes in the cortex that may be due to structural pathologies of synapses and their dendrites in the gray matter on the one hand and to pathologies in myelinating oligodendrocytes on the other. Here the possibility has been briefly examined that such a generalization might also hold for Autistic Spectrum Disorders (ASD). Evidence is presented that gray matter changes that accompany ASD may in fact reflect changes in synapses and subsequently of their dendrites, whereas those in the white matter reflect changes in myelination due to pathologies of oligodendrocytes. It is proposed that such structural pathologies during development provide a coherent biological model not only for the onset and course of ASD but also provide the basis for development and systematic evaluation of new treatment strategies.

Restoration of Normal Cerebral Oxygen Consumption with Rapamycin Treatment in a Rat Model of Autism-Tuberous Sclerosis

Tuberous sclerosis (TSC) is associated with autism spectrum disorders and has been linked to metabolic dysfunction and unrestrained signaling of the mammalian target of rapamycin (mTOR). Inhibition of mTOR by rapamycin can mitigate some of the phenotypic abnormalities associated with TSC and autism, but whether this is due to the mTOR-related function in energy metabolism remains to be elucidated. In young Eker rats, an animal model of TSC and autism, which harbors a germ line heterozygous Tsc2 mutation, we previously reported that cerebral oxygen consumption was pronouncedly elevated. Young (4 weeks) male control Long-Evans and Eker rats were divided into control and rapamycin-treated (20 mg/kg once daily for 2 days) animals. Cerebral regional blood flow ((14)C-iodoantipyrine) and O2 consumption (cryomicrospectrophotometry) were determined in isoflurane-anesthetized rats. We found significantly increased basal O2 consumption in the cortex (8.7 ± 1.5 ml O2/min/100 g Eker vs. 2.7 ± 0.2 control), hippocampus, pons and cerebellum. Regional cerebral blood flow and cerebral O2 extractions were also elevated in all brain regions. Rapamycin had no significant effect on O2 consumption in any brain region of the control rats, but significantly reduced consumption in the cortex (4.1 ± 0.3) and all other examined regions of the Eker rats. Phosphorylation of mTOR and S6K1 was similar in the two groups and equally reduced by rapamycin. Thus, a rapamycin-sensitive, mTOR-dependent but S6K1-independent, signal led to enhanced oxidative metabolism in the Eker brain. We found decreased Akt phosphorylation in Eker but not Long-Evans rat brains, suggesting that this may be related to the increased cerebral O2 consumption in the Eker rat. Our findings suggest that rapamycin targeting of Akt to restore normal cerebral metabolism could have therapeutic potential in tuberous sclerosis and autism.

A systematic review of molecular imaging (PET and SPECT) in autism spectrum disorder: current state and future research opportunities

Non-invasive positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are techniques used to quantify molecular interactions, biological processes and protein concentration and distribution. In the central nervous system, these molecular imaging techniques can provide critical insights into neurotransmitter receptors and their occupancy by neurotransmitters or drugs. In recent years, there has been an increase in the number of studies that have investigated neurotransmitters in autism spectrum disorder (ASD), while earlier studies mostly focused on cerebral blood flow and glucose metabolism. The underlying and contributing mechanisms of ASD are largely undetermined and ASD diagnosis relies on the behavioral phenotype. Discovery of biochemical endophenotypes would represent a milestone in autism research that could potentially lead to ASD subtype stratification and the development of novel therapeutic drugs. This review characterizes the prior use of molecular imaging by PET and SPECT in ASD, addresses methodological challenges and highlights areas of future opportunity for contributions from molecular imaging to understand ASD pathophysiology.

Insights from neuroenergetics into the interpretation of functional neuroimaging: an alternative empirical model for studying the brain's support of behavior

Functional neuroimaging measures quantitative changes in neurophysiological parameters coupled to neuronal activity during observable behavior. These results have usually been interpreted by assuming that mental causation of behavior arises from the simultaneous actions of distinct psychological mechanisms or modules. However, reproducible localization of these modules in the brain using functional magnetic resonance imaging (MRI) and positron emission tomography (PET) imaging has been elusive other than for sensory systems. In this paper, we show that neuroenergetic studies using PET, calibrated functional magnetic resonance imaging (fMRI), (13)C magnetic resonance spectroscopy, and electrical recordings do not support the standard approach, which identifies the location of mental modules from changes in brain activity. Of importance in reaching this conclusion is that changes in neuronal activities underlying the fMRI signal are many times smaller than the high ubiquitous, baseline neuronal activity, or energy in resting, awake humans. Furthermore, the incremental signal depends on the baseline activity contradicting theoretical assumptions about linearity and insertion of mental modules. To avoid these problems, while making use of these valuable results, we propose that neuroimaging should be used to identify observable brain activities that are necessary for a person's observable behavior rather than being used to seek hypothesized mental processes.

Kreativität bei Kindern und Jugendlichen mit Asperger Syndrom

Das Ziel der vorliegenden Studie war die systematische Erfassung der Kreativitätsleistung bei 5- bis 14-jährigen Jungen mit Asperger Syndrom im Vergleich mit einer gesunden Kontrollgruppe (je n=24). Untersucht wurden sowohl quantitative Kreativitätsaspekte (Ideenflüssigkeit, Ideenflexibilität) als auch qualitative Kreativitätsaspekte (Originalität) bei zwei Altersgruppen (jüngere Kinder: 5 – 9 Jahre, ältere Kinder/Jugendliche: 10 – 14 Jahre). Die Ergebnisse zeigen, dass bei Kindern/Jugendlichen mit Asperger Syndrom primär die quantitativen Aspekte der Kreativität beeinträchtigt sind (Ideenflüssigkeit und -flexibilität bei gleichbleibenden Items aus dem 5-Punkte Test), während die Kreativitätsleistung bei den abwechslungsreicheren Bildergänzungsaufgaben des Torrance Test of Creative Thinking, bei denen die Qualität/Originalität im Vordergrund steht, unbeeinträchtigt ist. In unserer Stichproben waren die Alterseffekte signifikant (jüngere Kinder zeigten schlechtere Leistungen), aber über die Gruppen vergleichbar (d. h. die Interaktionseffekte waren nicht signifikant). Im Sinne einer ressourcenorientierten Diagnostik, die für eine maßgeschneiderte Interventionsplanung unerlässlich ist, sollten also zusätzlich zu den quantitativen auch die qualitativen Aspekte kreativer und exekutiver Denkleistungen erfasst werden.

The BOLD signal and neurovascular coupling in autism

•

Neurovascular coupling and energy use may be changed in autism.

•

The relationship between neural activity and the BOLD signal may be altered in autism.

•

Simply comparing the BOLD signal of control and autistic people may not be meaningful.

•

Combined techniques will aid the interpretation of group differences in the BOLD signal.

BOLD (blood oxygen level dependent) fMRI (functional magnetic resonance imaging) is commonly used to study differences in neuronal activity between human populations. As the BOLD response is an indirect measure of neuronal activity, meaningful interpretation of differences in BOLD responses between groups relies upon a stable relationship existing between neuronal activity and the BOLD response across these groups. However, this relationship can be altered by changes in neurovascular coupling or energy consumption, which would lead to problems in identifying differences in neuronal activity. In this review, we focus on fMRI studies of people with autism, and comparisons that are made of their BOLD responses with those of control groups. We examine neurophysiological differences in autism that may alter neurovascular coupling or energy use, discuss recent studies that have used fMRI to identify differences between participants with autism and control participants, and explore experimental approaches that could help attribute between-group differences in BOLD signals to either neuronal or neurovascular factors.

Enzymes in the glutamate-glutamine cycle in the anterior cingulate cortex in postmortem brain of subjects with autism

BACKGROUND

Accumulating evidence suggests that dysfunction in the glutamatergic system may underlie the pathophysiology of autism. The anterior cingulate cortex (ACC) has been implicated in autism as well as in glutamatergic neurotransmission. We hypothesized that alterations in the glutamate-glutamine cycle in the ACC might play a role in the pathophysiology of autism.

METHODS

We performed Western blot analyses for the protein expression levels of enzymes in the glutamate-glutamine cycle, including glutamine synthetase, kidney-type glutaminase, liver-type glutaminase, and glutamate dehydrogenases 1 and 2, in the ACC of postmortem brain of individuals with autism (n = 7) and control subjects (n = 13).

RESULTS

We found that the protein levels of kidney-type glutaminase, but not those of the other enzymes measured, in the ACC were significantly lower in subjects with autism than in controls.

CONCLUSION

The results suggest that reduced expression of kidney-type glutaminase may account for putative alterations in glutamatergic neurotransmission in the ACC in autism.

Glutamatergic function in the resting awake human brain is supported by uniformly high oxidative energy

Rodent (13)C magnetic resonance spectroscopy studies show that glutamatergic signaling requires high oxidative energy in the awake resting state and allowed calibration of functional magnetic resonance imaging (fMRI) signal in terms of energy relative to the resting energy. Here, we derived energy used for glutamatergic signaling in the awake resting human. We analyzed human data of electroencephalography (EEG), positron emission tomography (PET) maps of oxygen (CMR(O2)) and glucose (CMR(glc)) utilization, and calibrated fMRI from a variety of experimental conditions. CMR(glc) and EEG in the visual cortex were tightly coupled over several conditions, showing that the oxidative demand for signaling was four times greater than the demand for nonsignaling events in the awake state. Variations of CMR(O2) and CMR(glc) from gray-matter regions and networks were within ±10% of means, suggesting that most areas required similar energy for ubiquitously high resting activity. Human calibrated fMRI results suggest that changes of fMRI signal in cognitive studies contribute at most ±10% CMR(O2) changes from rest. The PET data of sleep, vegetative state, and anesthesia show metabolic reductions from rest, uniformly >20% across, indicating no region is selectively reduced when consciousness is lost. Future clinical investigations will benefit from using quantitative metabolic measures.

Reduced effect of stimulation of AMPA receptors on cerebral O₂ consumption in a rat model of autism

Previous work demonstrated that basal alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor activity did not contribute to the elevated regional cerebral O₂ consumption in the brains of Eker rat (an autism-tuberous sclerosis model). We tested the hypothesis that increased stimulation of AMPA receptors also would not augment cerebral O₂ consumption in the Eker rat. Three cortical sites were prepared for administration of saline, 10⁻⁴ and 10⁻³ M AMPA in young (4 weeks) male control Long Evans and Eker rats (70-100 g). Cerebral blood flow (¹⁴C-iodoantipyrine) and O₂ consumption (cryomicrospectrophotometry) were determined in isoflurane anesthetized rats. Receptor levels were studied through Western analysis of the GLuR1 subunit of the AMPA receptor. We found significantly increased cortical O₂ consumption (+33%) after 10⁻⁴ M AMPA in control rats. The higher dose of AMPA did not further increase consumption. In the Eker rats, neither dose led to a significant increase in cortical O₂ consumption. Regional blood flow followed a similar pattern to oxygen consumption but cortical O₂ extraction did not differ. Cortical AMPA receptor protein levels were significantly reduced (-21%) in the Eker compared to control rats. Both O₂ consumption and blood flow were significantly elevated in the pons of the Eker rats compared to control. These data demonstrate a reduced importance of AMPA receptors in the control of cortical metabolism, related to reduced AMPA receptor protein, in the Eker rat. This suggests that increasing AMPA receptor activity may not be an effective treatment for children with autism spectrum disorders as they also have reduced AMPA receptor number.

Brief Report: alterations in cerebral blood flow as assessed by PET/CT in adults with autism spectrum disorder with normal IQ

Specific biological markers for autism spectrum disorder (ASD) have not yet been established. Functional studies have shown abnormalities in the anatomo-functional connectivity of the limbic-striatal "social" brain. This study aimed to investigate regional cerebral blood flow (rCBF) at rest. Thirteen patients with ASD of normal intelligence and ten IQ-, sex- and age-matched healthy controls (HC) underwent PET/CT using [1-(11)C]butanol, a perfusion tracer. As compared to HC, ASD showed significant CBF increases in the right parahippocampal, posterior cingulate, primary visual and temporal cortex, putamen, caudatus, substantia nigra and cerebellum. No statistically significant correlation between CBF and IQ was found. The limbic, posterior associative and cerebellar cortices showed increased blood flow in ASD, confirming previous findings about the neurobiology of ASD.

Proton magnetic resonance spectroscopy and MRI reveal no evidence for brain mitochondrial dysfunction in children with autism spectrum disorder

Brain mitochondrial dysfunction has been proposed as an etiologic factor in autism spectrum disorder (ASD). Proton magnetic resonance spectroscopic imaging ((1)HMRS) and MRI were used to assess for evidence of brain mitochondrial dysfunction in longitudinal samples of children with ASD or developmental delay (DD), and cross-sectionally in typically developing (TD) children at 3-4, 6-7 and 9-10 years-of-age. A total of 239 studies from 130 unique participants (54ASD, 22DD, 54TD) were acquired. (1)HMRS and MRI revealed no evidence for brain mitochondrial dysfunction in the children with ASD. Findings do not support a substantive role for brain mitochondrial abnormalities in the etiology or symptom expression of ASD, nor the widespread use of hyperbaric oxygen treatment that has been advocated on the basis of this proposed relationship.

Involvement of the anterior thalamic radiation in boys with high functioning autism spectrum disorders: a Diffusion Tensor Imaging study

BACKGROUND

Autism has been hypothesized to reflect neuronal disconnection. Several recent reports implicate the key thalamic relay nuclei and cortico-thalamic connectivity in the pathophysiology of autism. Accordingly, we aimed to focus on evaluating the integrity of the thalamic radiation and sought to replicate prior white matter findings in Korean boys with high-functioning autism spectrum disorders (ASD) using Diffusion Tensor Imaging (DTI).

METHODS

We compared fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) in 17 boys with ASD and 17 typically developing controls in the anterior thalamic radiation (ATR), superior thalamic radiation (STR), posterior thalamic radiation (PTR), corpus callosum (CC), uncinate fasciculus (UF) and inferior longitudinal fasciculus (ILF).

RESULTS

The two groups were group-matched on age, IQ, handedness and head circumference. In whole-brain voxel-wise analyses, FA was significantly reduced and MD was significantly increased in the right ATR, CC, and left UF in subjects with ASD (p<0.05, corrected). We found significantly lower FA in right and left ATR, CC, left UF and right and left ILF and significantly higher MD values of the CC in the ASD group in region of interest-based analyses. We also observed significantly higher RD values of right and left ATR, CC, left UF, left ILF in subjects with ASD compared to typically developing boys and significantly lower AD values of both ILF. Right ATR and right UF FA was significantly negatively correlated with total SRS score within the ASD group (r=-.56, p=.02).

CONCLUSIONS

Our preliminary findings support evidence implicating disturbances in the thalamo-frontal connections in autism. These findings highlight the role of hypoconnectivity between the frontal cortex and thalamus in ASD.

Atypical neural self-representation in autism

The 'self' is a complex multidimensional construct deeply embedded and in many ways defined by our relations with the social world. Individuals with autism are impaired in both self-referential and other-referential social cognitive processing. Atypical neural representation of the self may be a key to understanding the nature of such impairments. Using functional magnetic resonance imaging we scanned adult males with an autism spectrum condition and age and IQ-matched neurotypical males while they made reflective mentalizing or physical judgements about themselves or the British Queen. Neurotypical individuals preferentially recruit the middle cingulate cortex and ventromedial prefrontal cortex in response to self compared with other-referential processing. In autism, ventromedial prefrontal cortex responded equally to self and other, while middle cingulate cortex responded more to other-mentalizing than self-mentalizing. These atypical responses occur only in areas where self-information is preferentially processed and does not affect areas that preferentially respond to other-referential information. In autism, atypical neural self-representation was also apparent via reduced functional connectivity between ventromedial prefrontal cortex and areas associated with lower level embodied representations, such as ventral premotor and somatosensory cortex. Furthermore, the magnitude of neural self-other distinction in ventromedial prefrontal cortex was strongly related to the magnitude of early childhood social impairments in autism. Individuals whose ventromedial prefrontal cortex made the largest distinction between mentalizing about self and other were least socially impaired in early childhood, while those whose ventromedial prefrontal cortex made little to no distinction between mentalizing about self and other were the most socially impaired in early childhood. These observations reveal that the atypical organization of neural circuitry preferentially coding for self-information is a key mechanism at the heart of both self-referential and social impairments in autism.

The anatomy of extended limbic pathways in Asperger syndrome: a preliminary diffusion tensor imaging tractography study

It has been suggested that people with autistic spectrum disorder (ASD) have altered development (and connectivity) of limbic circuits. However, direct evidence of anatomical differences specific to white matter pathways underlying social behaviour and emotions in ASD is lacking. We used Diffusion Tensor Imaging Tractography to compare, in vivo, the microstructural integrity and age-related differences in the extended limbic pathways between subjects with Asperger syndrome and healthy controls. Twenty-four males with Asperger syndrome (mean age 23+/-12 years, age range: 9-54 years) and 42 age-matched male controls (mean age 25+/-10 years, age range: 9-54 years) were studied. We quantified tract-specific diffusivity measurements as indirect indexes of microstructural integrity (e.g. fractional anisotropy, FA; mean diffusivity, MD) and tract volume (e.g. number of streamlines) of the main limbic tracts. The dissected limbic pathways included the inferior longitudinal fasciculus, inferior frontal occipital fasciculus, uncinate, cingulum and fornix. There were no significant between-group differences in FA and MD. However, compared to healthy controls, individuals with Asperger syndrome had a significantly higher number of streamlines in the right (p=.003) and left (p=.03) cingulum, and in the right (p=.03) and left (p=.04) inferior longitudinal fasciculus. In contrast, people with Asperger syndrome had a significantly lower number of streamlines in the right uncinate (p=.02). Within each group there were significant age-related differences in MD and number of streamlines, but not FA. However, the only significant age-related between-group difference was in mean diffusivity of the left uncinate fasciculus (Z(obs)=2.05) (p=.02). Our preliminary findings suggest that people with Asperger syndrome have significant differences in the anatomy, and maturation, of some (but not all) limbic tracts.

Cerebral O(2) consumption in young Eker rats, effects of GABA blockade: implications for autism

Since there is a strong correlation between tuberous sclerosis and autism, we used a tuberous sclerosis model (Eker rat) to test the hypothesis that the increased regional cerebral O(2) consumption in the Eker rat might be associated with autism. We also examined whether this increased cerebral O(2) consumption was related to changes in the activity of the gamma-aminobutyric acid (GABA) inhibitory system. Young (4 weeks) male control Long Evans (n=14) and Eker (n=14) rats (70-100g) were divided into control and bicuculline (1mg/kg/min for 2 min then 0.1mg/kg/min for 13 min, GABA(A) receptor antagonist) treated animals. Cerebral regional blood flow ((14)C-iodoantipyrine) and O(2) consumption (cryomicrospectrophotometry) were determined in isoflurane anesthetized rats. We found significantly increased basal O(2) consumption in the cortex (6.3+/-0.7 ml O(2)/min/100g Eker vs. 5.1+/-0.2 ml O(2)/min/100g control), hippocampus and cerebellum, but not the pons. Regional cerebral blood flow was also elevated in the cortex and hippocampus in Eker rats at baseline, but cerebral O(2) extractions were similar. Bicuculline significantly increased O(2) consumption in the cortex (6.5+/-0.3) and all other regions of the control rats, but had no effect on cortex (5.9+/-1.5) or other regions of the Eker rats. Cerebral blood flow followed a similar pattern. In conclusion, Eker rats had significantly elevated cerebral O(2) consumption and blood flow, but this was not affected by GABA receptor blockade. This suggested a reduced activity of the GABA(A) receptor in the brains of Eker rats. This may have important implications in the treatment of autism.

Beyond pragmatics: morphosyntactic development in autism

Language acquisition research in autism has traditionally focused on high-level pragmatic deficits. Few studies have examined grammatical abilities in autism, with mixed findings. The present study addresses this gap in the literature by providing a detailed investigation of syntactic and higher-level discourse abilities in verbal children with autism, age 5 years. Findings indicate clear language difficulties that go beyond what would be expected based on developmental level; specifically, syntactic delays, impairments in discourse management and increased production of non-meaningful words (jargon). The present study indicates a highly specific pattern of language impairments, and importantly, syntactic delays, in a group of children with autism carefully matched on lexical level and non-verbal mental age with children with developmental delays and typical development.

Autism with facial port-wine stain: a new syndrome?

The hallmark of Sturge-Weber syndrome is leptomeningeal angiomatosis. Over 15 years, four children were identified (2 boys, age 2.9-6 years) with unilateral facial port-wine stain, referred for presumable Sturge-Weber syndrome but who were also autistic. Computed tomography and magnetic resonance imaging scans failed to show evidence of leptomeningeal angioma in all four children. Three of the children had a history of seizures. Detailed neuropsychologic testing of three children revealed a similar presentation, characterized by developmental disturbance, particularly involving delayed onset of language, and early-emerging social atypicality. Positron emission tomography scanning of cerebral glucose metabolism revealed hypometabolism in the bilateral medial temporal regions, anterior cingulate gyrus, frontal cortex, right temporal cortex, and cerebellum. The pattern of glucose hypometabolism differed from that of 12 children with infantile autism (age 2.7-7.9 years) who had mild left medial temporal but more severe right temporal cortical hypometabolism and showed a reversal of normal frontotemporal asymmetry of glucose metabolism. Unilateral facial port-wine stain and autism with no intracranial angioma on conventional imaging may represent a rare clinical entity distinct from both infantile autism and previously described variants of Sturge-Weber syndrome.

Increased cerebral oxygen consumption in Eker rats and effects of N-methyl-D-aspartate blockade: Implications for autism

Because there is a strong correlation between tuberous sclerosis and autism, we used a tuberous sclerosis model (Eker rat) to test the hypothesis that these animals would have an altered regional cerebral O2 consumption that might be associated with autism. We also examined whether the altered cerebral O2 consumption was related to changes in the importance of N-methyl-D-aspartate (NMDA) receptors. Young (4 weeks) male control Long Evans (N = 14) and Eker (N = 14) rats (70-100 g) were divided into control and CGS-19755 (10 mg/kg, competitive NMDA antagonist)-treated animals. Cerebral regional blood flow (14C-iodoantipyrine) and O2 consumption (cryomicrospectrophotometry) were determined in isoflurane-anesthetized rats. NMDA receptor protein levels were determined by Western immunoblotting. We found significantly increased basal O2 consumption in the cortex (6.2 +/- 0.6 ml O2/min/100 g Eker vs. 4.7 +/- 0.4 Long Evans), hippocampus, cerebellum, and pons. Regional cerebral blood flow was also elevated in Eker rats at baseline, but cerebral O2 extraction was similar. CGS-19755 significantly lowered O2 consumption in the cortex (2.8 +/- 0.3), hippocampus, and pons of the Long Evans rats but had no effect on cortex (5.8 +/- 0.8) or other regions of the Eker rats. Cerebral blood flow followed a similar pattern. NMDA receptor protein levels (NR1 subunit) were similar between groups. In conclusion, Eker rats had significantly elevated cerebral O2 consumption and blood flow, but this was not related to NMDA receptor activation. In fact, the importance of NMDA receptors in the control of basal cerebral O2 consumption was reduced. This might have important implications in the treatment of autism.

[Autism: neuroimaging]

Autism is a neurodevelopmental disorder with a range of clinical presentations. These presentations vary from mild to severe and are referred to as autism spectrum disorders. The most common clinical sign of autism spectrum disorders is social interaction impairment, which is associated with verbal and non-verbal communication deficits and stereotyped and repetitive behaviors. Thanks to recent brain imaging studies, scientists are getting a better idea of the neural circuits involved in autism spectrum disorders. Indeed, functional brain imaging, such as positron emission tomography, single foton emission tomography and functional MRI have opened a new perspective to study normal and pathological brain functioning. Three independent studies have found anatomical and rest functional temporal lobe abnormalities in autistic patients. These alterations are localized in the superior temporal sulcus bilaterally, an area which is critical for perception of key social stimuli. In addition, functional studies have shown hypoactivation of most areas implicated in social perception (face and voice perception) and social cognition (theory of mind). These data suggest an abnormal functioning of the social brain network in autism. The understanding of the functional alterations of this important mechanism may drive the elaboration of new and more adequate social re-educative strategies for autistic patients.

Neural correlates of executive function in autistic spectrum disorders

BACKGROUND

Some clinical characteristics of high-functioning individuals with autistic spectrum disorder (ASD) such as repetitive stereotyped behaviors, perseveration, and obsessionality have been related to executive function (EF) deficits, more specifically to deficits in inhibitory control and set shifting and mediating frontostriatal neural pathways. However, to date, no functional imaging study on ASD has investigated inhibition and cognitive flexibility and no one has related EF brain activation to brain structure.

METHODS

We compared brain activation (using functional magnetic resonance imaging) in 10 normal intelligence adults with ASD and 12 healthy control subjects during three different EF tasks: 1) motor-inhibition (GO/NO-GO); 2) cognitive interference-inhibition (spatial STROOP); and 3) set shifting (SWITCH). Using voxel-based morphometry, we investigated if cortical areas which were functionally different in people with ASD were also anatomically abnormal.

RESULTS

Compared with control subjects, ASD individuals showed significantly increased brain activation in 1) left inferior and orbital frontal gyrus (motor-inhibition); 2) left insula (interference-inhibition); and 3) parietal lobes (set shifting). Moreover, in individuals with ASD, increased frontal gray matter density and increased functional activation shared the same anatomical location.

CONCLUSIONS

Our findings suggest an association between successful completion of EF tasks and increased brain activation in people with ASD, which partially may be explained by differences in brain anatomy.

Neuroimaging in disorders of social and emotional functioning: what is the question?

Social and emotional processing uses neural systems involving structures ranging from the brain stem to the associational cortex. Neuroimaging research has attempted to identify abnormalities in components of these systems that would underlie the behavioral abnormalities seen in disorders of social and emotional processing, notably autism spectrum disorders, the focus of this review. However, the findings have been variable. The most replicated anatomic finding (a tendency toward large brains) is not modular, and metabolic imaging and functional imaging (although showing substantial atypicality in activation) are not consistent regarding specific anatomic sites. Moreover, autism spectrum disorder demonstrates substantial heterogeneity on multiple levels. Here evidence is marshaled from a review of neuroimaging data to support the claim that abnormalities in social and emotional processing on the autism spectrum are a consequence of systems disruptions in which the behaviors are a final common pathway and the focal findings can be variable, downstream of other pathogenetic mechanisms, and downstream of more pervasive abnormalities.

Cerebellar function in autism: functional magnetic resonance image activation during a simple motor task

BACKGROUND

The cerebellum is one of the most consistent sites of neuroanatomic abnormality in autism, yet it is still unclear how such pathology impacts cerebellar function. In normal subjects, we previously demonstrated with functional magnetic resonance imaging (fMRI) a dissociation between cerebellar regions involved in attention and those involved in a simple motor task, with motor activation localized to the anterior cerebellum ipsilateral to the moving hand. The purpose of the present investigation was to examine activation in the cerebella of autistic patients and normal control subjects performing this motor task.

METHODS

We studied eight autistic patients and eight matched normal subjects, using fMRI. An anatomic region-of-interest approach was used, allowing a detailed examination of cerebellar function.

RESULTS

Autistic individuals showed significantly increased motor activation in the ipsilateral anterior cerebellar hemisphere relative to normal subjects, in addition to atypical activation in contralateral and posterior cerebellar regions. Moreover, increased activation was correlated with the degree of cerebellar structural abnormality.

CONCLUSIONS

These findings strongly suggest dysfunction of the autistic cerebellum that is a reflection of cerebellar anatomic abnormality. This neurofunctional deficit might be a key contributor to the development of certain diagnostic features of autism (e.g., impaired communication and social interaction, restricted interests, and stereotyped behaviors).

Proton magnetic resonance spectroscopic imaging of the brain in childhood autism

BACKGROUND

Autism is a developmental disorder of unknown neurologic basis. Based on prior work, we used proton magnetic resonance spectroscopic imaging ((1)H- MRSI) to investigate brain structures, including cingulate and caudate, that we hypothesized would reveal metabolic abnormalities in subjects with autism.

METHODS

In 22 children with autism, 5 to 16 years old, and 20 age-matched healthy control subjects, (1)H-MRSI assessed levels of N-acetyl compounds (NAA), choline compounds (Cho), and creatine plus phosphocreatine (Cr) at 272 msec echo-time and 1.5 T.

RESULTS

In subjects with autism compared with control subjects, Cho was 27.2% lower in left inferior anterior cingulate and 19.1% higher in the head of the right caudate nucleus; Cr was 21.1% higher in the head of the right caudate nucleus, but lower in the body of the left caudate nucleus (17.9%) and right occipital cortex (16.6%).

CONCLUSIONS

Results are consistent with altered membrane metabolism, altered energetic metabolism, or both in the left anterior cingulate gyrus, both caudate nuclei, and right occipital cortex in subjects with autism compared with control subjects.

Brain glucose metabolism in Rett Syndrome

Rett syndrome is a progressive neurologic disorder affecting girls in early childhood with loss of achieved psychomotor abilities and mental retardation. Six sedated female patients (4 to 15 years of age) with a diagnosis of Rett syndrome were studied with [(18)F]fluorodeoxyglucose (FDG) and underwent positron emission tomography scanning of the brain. Relative tracer concentrations between different areas of the brain were assessed, and results were compared with 18 age-matched control subjects. Patients were divided into two age groups: 3 to 8 years of age and 9 to 15 years of age. A relative decrease in [(18)F]FDG uptake in the lateral occipital areas in relation with the whole brain and a relative increase in the cerebellum was evident in both age groups (P < 0.001, unpaired Student t test). A relative increase in frontal tracer uptake was observed in the younger group. Sensorimotor areas and relations between cortical and subcortical structures were preserved in all patients. Changes in glucose cerebral metabolism resemble the regional distribution of normal children less than 1 year of age, likely reflecting a maturational arrest. Changes in frontal areas parallel those in postmortem N-methyl-D-aspartate receptor densities and could correlate with different clinical stages of the disease. This pattern differs from those described in Down syndrome, autism, and Alzheimer's disease.

Brain imaging in neurobehavioral disorders

Neuroimaging studies of neurobehavioral disorders are using new imaging modalities. In dyslexia, anatomic imaging studies demonstrate an abnormal symmetry of the planum temporale. Functional imaging supports the hypothesis that developmental dyslexia is frequently the result of deficits in phonologic processing and that normal reading requires a patent network organization of a number of anterior and posterior brain areas. In autism, anatomic imaging studies are conflicting. Functional imaging demonstrates temporal lobe abnormalities and abnormal interaction between frontal and parietal brain areas. In attention-deficit-hyperactivity disorder, imaging studies suggest an abnormality in the prefrontal and striatal regions. Neuroimaging studies are often contradictory, but trends, especially with functional imaging analysis, are evolving. Because neurobehavioral disorders seem to be a result of a dysfunction in brain circuits, no one region will be abnormal in all patients studied. Further studies with well-defined patient populations and appropriate activation paradigms will better elucidate the pathophysiology of these conditions.

Single-photon emission computed tomography of the brain in autism: effect of the developmental level

Brain single-photon emission computed tomography was performed in 22 autistic and 10 nonautistic disabled patients. The regional cerebral blood flow in both laterotemporal and dorso-medio-lateral frontal areas decreased significantly in the autistic group compared with in nonautistic group. In the autistic group, the regional cerebral blood flow was significantly higher in the right temporal and right parietal lobes than that in the left ones. Inversely, the regional cerebral blood flow in the frontal and occipital lobes was significantly higher on the left side than on the right side. In the nonautistic group, except for in the dorso-medio-lateral frontal lobes (left > right), there was no difference in the regional cerebral blood flow in either cerebrum or cerebellum. A positive correlationship between regional cerebral flow and development quotient (intelligence quotient) was observed in the left laterotemporal and both dorso-medio-lateral frontal areas, and a negative one was observed in the cerebellar vermis area. These results suggest that the regional cerebral blood flow decrease in the temporal and frontal areas relates to not only the brain mechanism of autism reported previously but also intelligence levels.

Functional neuroimaging of autistic disorders

Functional neuroimaging methods hold promise for elucidating the neurobiology of autistic disorders, yet they present difficult practical and scientific challenges when applied to these complex and heterogeneous syndromes. Single-state studies of brain metabolism and blood flow thus far have failed to yield consistent findings, but suggest considerable variability in regional patterns of cerebral synaptic activity. Patients with idiopathic autism are less likely to show abnormalities than are patients with comorbid illness or epilepsy. Activation studies have begun to suggest alterations in brain organization for language and cognition. Neurotransmitter studies using positron emission tomography (PET) suggest abnormalities of serotonergic and dopaminergic function. Studies using magnetic resonance spectroscopy (MRS) have begun to document metabolic deficits in the frontal cortex and cerebellum. A single study using magnetoencephalography suggests a high incidence of epileptiform activity in children with autistic regression. Research needs include well-controlled developmental studies, particularly of young subjects and relatively homogeneous subgroups, which balance scientific rigor with ethical constraints. Investigations of the serotonergic and dopaminergic systems, limbic-based memory and emotional systems, and the role of epileptiform activity in autism represent priorities for future research.