Regional cerebral glucose metabolism and attention in adults with a history of childhood 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.

From Neurodevelopmental to Neurodegenerative Disorders: The Vascular Continuum

Structural and functional integrity of the cerebral vasculature ensures proper brain development and function, as well as healthy aging. The inability of the brain to store energy makes it exceptionally dependent on an adequate supply of oxygen and nutrients from the blood stream for matching colossal demands of neural and glial cells. Key vascular features including a dense vasculature, a tightly controlled environment, and the regulation of cerebral blood flow (CBF) all take part in brain health throughout life. As such, healthy brain development and aging are both ensured by the anatomical and functional interaction between the vascular and nervous systems that are established during brain development and maintained throughout the lifespan. During critical periods of brain development, vascular networks remodel until they can actively respond to increases in neural activity through neurovascular coupling, which makes the brain particularly vulnerable to neurovascular alterations. The brain vasculature has been strongly associated with the onset and/or progression of conditions associated with aging, and more recently with neurodevelopmental disorders. Our understanding of cerebrovascular contributions to neurological disorders is rapidly evolving, and increasing evidence shows that deficits in angiogenesis, CBF and the blood-brain barrier (BBB) are causally linked to cognitive impairment. Moreover, it is of utmost curiosity that although neurodevelopmental and neurodegenerative disorders express different clinical features at different stages of life, they share similar vascular abnormalities. In this review, we present an overview of vascular dysfunctions associated with neurodevelopmental (autism spectrum disorders, schizophrenia, Down Syndrome) and neurodegenerative (multiple sclerosis, Huntington's, Parkinson's, and Alzheimer's diseases) disorders, with a focus on impairments in angiogenesis, CBF and the BBB. Finally, we discuss the impact of early vascular impairments on the expression of neurodegenerative diseases.

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.

Evaluating Functional Connectivity Alterations in Autism Spectrum Disorder Using Network-Based Statistics

The study of resting-state functional brain networks is a powerful tool to understand the neurological bases of a variety of disorders such as Autism Spectrum Disorder (ASD). In this work, we have studied the differences in functional brain connectivity between a group of 74 ASD subjects and a group of 82 typical-development (TD) subjects using functional magnetic resonance imaging (fMRI). We have used a network approach whereby the brain is divided into discrete regions or nodes that interact with each other through connections or edges. Functional brain networks were estimated using the Pearson’s correlation coefficient and compared by means of the Network-Based Statistic (NBS) method. The obtained results reveal a combination of both overconnectivity and underconnectivity, with the presence of networks in which the connectivity levels differ significantly between ASD and TD groups. The alterations mainly affect the temporal and frontal lobe, as well as the limbic system, especially those regions related with social interaction and emotion management functions. These results are concordant with the clinical profile of the disorder and can contribute to the elucidation of its neurological basis, encouraging the development of new clinical approaches.

Positron emission tomography assessment of cerebral glucose metabolic rates in autism spectrum disorder and schizophrenia

Several models have been proposed to account for observed overlaps in clinical features and genetic predisposition between schizophrenia and autism spectrum disorder. This study assessed similarities and differences in topological patterns and vectors of glucose metabolism in both disorders in reference to these models. Co-registered 18fluorodeoxyglucose PET and MRI scans were obtained in 41 schizophrenia, 25 ASD, and 55 healthy control subjects. AFNI was used to map cortical and subcortical regions of interest. Metabolic rates were compared between three diagnostic groups using univariate and multivariate repeated-measures ANOVA. Compared to controls, metabolic rates in schizophrenia subjects were decreased in the frontal lobe, anterior cingulate, superior temporal gyrus, amygdala and medial thalamic nuclei; rates were increased in the occipital cortex, hippocampus, basal ganglia and lateral thalamic nuclei. In ASD subjects metabolic rates were decreased in the parietal lobe, frontal premotor and eye-fields areas, and amygdala; rates were increased in the posterior cingulate, occipital cortex, hippocampus and basal ganglia. In relation to controls, subjects with ASD and schizophrenia showed opposite changes in metabolic rates in the primary motor and somatosensory cortex, anterior cingulate and hypothalamus; similar changes were found in prefrontal and occipital cortices, inferior parietal lobule, amygdala, hippocampus, and basal ganglia. Schizophrenia and ASD appear to be associated with a similar pattern of metabolic abnormalities in the social brain. Divergent maladaptive trade-offs, as postulated by the diametrical hypothesis of their evolutionary relationship, may involve a more circumscribed set of anterior cingulate, motor and somatosensory regions and the specific cognitive functions they subserve.

Auditory attention in autism spectrum disorder: An exploration of volumetric magnetic resonance imaging findings

Studies have shown that individuals with autism spectrum disorder (ASD) tend to perform significantly below typically developing individuals on standardized measures of attention, even when controlling for IQ. The current study sought to examine within ASD whether anatomical correlates of attention performance differed between those with average to above-average IQ (AIQ group) and those with low-average to borderline ability (LIQ group) as well as in comparison to typically developing controls (TDC). Using automated volumetric analyses, we examined regional volume of classic attention areas including the superior frontal gyrus, anterior cingulate cortex, and precuneus in ASD AIQ (n = 38) and LIQ (n = 18) individuals along with 30 TDC. Auditory attention performance was assessed using subtests of the Test of Memory and Learning (TOMAL) compared among the groups and then correlated with regional brain volumes. Analyses revealed group differences in attention. The three groups did not differ significantly on any auditory attention-related brain volumes; however, trends toward significant size-attention function interactions were observed. Negative correlations were found between the volume of the precuneus and auditory attention performance for the AIQ ASD group, indicating larger volume related to poorer performance. Implications for general attention functioning and dysfunctional neural connectivity in ASD are discussed.

Atypical lateralization of motor circuit functional connectivity in children with autism is associated with motor deficits

Background

Atypical lateralization of language-related functions has been repeatedly found in individuals with autism spectrum conditions (ASC). Few studies have, however, investigated deviations from typically occurring asymmetry of other lateralized cognitive and behavioural domains. Motor deficits are among the earliest and most prominent symptoms in individuals with ASC and precede core social and communicative symptoms.

Methods

Here, we investigate whether motor circuit connectivity is (1) atypically lateralized in children with ASC and (2) whether this relates to core autistic symptoms and motor performance. Participants comprised 44 right-handed high-functioning children with autism (36 males, 8 females) and 80 typically developing control children (58 males, 22 females) matched on age, sex and performance IQ. We examined lateralization of functional motor circuit connectivity based on homotopic seeds derived from peak activations during a finger tapping paradigm. Motor performance was assessed using the Physical and Neurological Examination for Subtle Signs (PANESS).

Results

Children with ASC showed rightward lateralization in mean motor circuit connectivity compared to typically developing children, and this was associated with poorer performance on all three PANESS measures.

Conclusions

Our findings reveal that atypical lateralization in ASC is not restricted to language functions but is also present in circuits subserving motor functions and may underlie motor deficits in children with ASC. Future studies should investigate whether this is an age-invariant finding extending to adolescents and adults and whether these asymmetries relate to atypical lateralization in the language domain.

Electronic supplementary material

The online version of this article (doi:10.1186/s13229-016-0096-6) contains supplementary material, which is available to authorized users.

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

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.

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.

Psychological correlates of handedness and corpus callosum asymmetry in autism: the left hemisphere dysfunction theory revisited

Rightward cerebral lateralization has been suggested to be involved in the neuropathology of autism spectrum conditions. We investigated functional and neuroanatomical asymmetry, in terms of handedness and corpus callosum measurements in male adolescents with autism, their unaffected siblings and controls, and their associations with executive dysfunction and symptom severity. Adolescents with autism did not differ from controls in functional asymmetry, but neuroanatomically showed the expected pattern of stronger rightward lateralization in the posterior and anterior midbody based on their hand-preference. Measures of symptom severity were related to rightward asymmetry in three subregions (splenium, posterior midbody and rostral body). We found the opposite pattern for the isthmus and rostrum with better cognitive and less severe clinical scores associated with rightward lateralization.

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.

Functional deficits of the attentional networks in autism

Attentional dysfunction is among the most consistent observations of autism spectrum disorders (ASD). However, the neural nature of this deficit in ASD is still unclear. In this study, we aimed to identify the neurobehavioral correlates of attentional dysfunction in ASD. We used the Attention Network Test-Revised and functional magnetic resonance imaging to examine alerting, orienting, and executive control functions, as well as the neural substrates underlying these attentional functions in unmedicated, high-functioning adults with ASD (n = 12) and matched healthy controls (HC, n = 12). Compared with HC, individuals with ASD showed increased error rates in alerting and executive control, accompanied by lower activity in the mid-frontal gyrus and the caudate nucleus for alerting, and by the absence of significant functional activation in the anterior cingulate cortex (ACC) for executive control. In addition, greater behavioral deficiency in executive control in ASD was correlated with less functional activation of the ACC. These findings of behavioral and neural abnormalities in alerting and executive control of attention in ASD may suggest core attentional deficits, which require further investigation.

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.

Treatment with levetiracetam in a patient with pervasive developmental disorders, severe intellectual disability, self-injurious behavior, and seizures: a case report

Pervasive developmental disorder is characterized by various symptoms that often include self-injurious behavior (SIB). Episodes of SIB occur in the context of high emotional arousal, anger, or fear and may be related to epilepsy. We report the case of a 20-year-old man with pervasive developmental disorder presenting with SIB non-responsive to antipsychotic medication. Positron emission tomography showed a right temporoparietal hypometabolic focal lesion suggestive of an epileptic focus. Two weeks after initiation of levetiracetam (Keppra®), SIB disappeared, without recurrence 24 months later. Levetiracetam (Keppra®) may be beneficial for such patients.

MR diffusion tensor imaging: a window into white matter integrity of the working brain

As Norman Geschwind asserted in 1965, syndromes resulting from white matter lesions could produce deficits in higher-order functions and "disconnexion" or the interruption of connection between gray matter regions could be as disruptive as trauma to those regions per se. The advent of in vivo diffusion tensor imaging, which allows quantitative characterization of white matter fiber integrity in health and disease, has served to strengthen Geschwind's proposal. Here we present an overview of the principles of diffusion tensor imaging (DTI) and its contribution to progress in our current understanding of normal and pathological brain function.

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.

Technetium-99m HMPAO brain SPECT in autistic children and their families

The purpose of the study was to investigate perfusion patterns in autistic children (AC) and their families. Ten AC (9 boys, 1 girl; mean age: 6.9+/-1.7 years) with autistic disorder defined by DSM-III-R criteria, five age-matched children (3 boys, 2 girls) as a control group, and the immediate family members of eight AC (8 mothers, 8 fathers, 7 siblings; mean ages: 39+/-4 years, 36+/-5 years and 13+/-5 years, respectively) were included in the study. Age- and sex-matched control groups for both the parents and the siblings were also included in the study. Brain perfusion images were obtained 1 h after the intravenous injection of an adjusted dose of Tc-99m HMPAO to children and the adults. Visual and semiquantitative evaluations were performed. Hypoperfusion was seen in the right posterior parietal cortex in three AC, in bilateral parietal cortex in one AC, bilateral frontal cortex in two AC, left parietal and temporal cortex in one AC, and right parietal and temporal cortex in one AC. Asymmetric perfusion was observed in the caudate nucleus in four AC. In semiquantitative analyses, statistically significant hypoperfusion was found in the right inferior and superior frontal, left superior frontal, right parietal, right mesial temporal and right caudate nucleus. In parents of AC, significant hypoperfusion was noted in the right parietal and bilateral inferior frontal cortex. In siblings of AC, perfusion in the right frontal cortex, right nucleus caudate and left parietal cortex was significantly decreased. This preliminary study suggests the existence of regional brain perfusion alterations in frontal, temporal, and parietal cortex and in caudate nucleus in AC and in their first-degree family members.

Regional cerebral blood flow in childhood autism: a SPET study with SPM evaluation

AIM

To establish a link between rCBF assessed with Tc-ECD SPET and the clinical manifestation of the disease.

METHODS

We performed the study on 11 patients (five girls and six boys; mean age 11.2 years) displaying autistic behaviour and we compared their data with that of an age-matched reference group of eight normal children. A quantitative analysis of rCBF was performed calculating a perfusion index (PI) and an asymmetry index (AI) in each lobe. Images were analysed with statistical parametric mapping software, following the spatial normalization of SPET images for a standard brain.

RESULTS

A statistically significant (P=0.003) global reduction of CBF was found in the group of autistic children (PI=1.07+/-0.07) when compared with the reference group (PI=1.25+/-0.12). Moreover, a significant difference was also observed for the right-to-left asymmetry of hemispheric perfusion between the control group and autistic patients (P=0.0085) with a right prevalence greater in autistic (2.90+/-1.68) with respect to normal children (1.12+/-0.49). Our data show a significant decrease of global cerebral perfusion in autistic children in comparison with their normal counterparts and the existence of left-hemispheric dysfunction, especially in the temporo-parietal areas devoted to language and the comprehension of music and sounds.

CONCLUSION

We suggest that these abnormal areas are related to the cognitive impairment observed in autistic children, such as language deficits, impairment of cognitive development and object representation, and abnormal perception and responses to sensory stimuli. Tc-ECD SPET seems to be sensitive in revealing brain blood flow alterations and left-to-right asymmetries, when neuroradiological patterns are normal.

A neurobehavioral examination of individuals with high-functioning autism and Asperger's disorder using a fronto-striatal model of dysfunction

The repetitive, stereotyped, and obsessive behaviors that characterize autism may in part be attributable to disruption of the region of the fronto-striatal system, which mediates executive abilities. Neuropsychological testing has shown that children with autism exhibit set-shifting deficiencies on tests such as the Wisconsin Card Sorting task but show normal inhibitory ability on variants of the Stroop color-word test. According to Minshew and Goldstein's multiple primary deficit theory, the complexity of the executive functioning task is important in determining the performance of individuals with autism. This study employed a visual-spatial task (with a Stroop-type component) to examine the integrity of executive functioning, in particular inhibition, in autism (n = 12) and Asperger's disorder (n = 12) under increasing levels of cognitive complexity. Whereas the Asperger's disorder group performed similarly to age- and IQ-matched control participants, even at the higher levels of cognitive complexity, the high-functioning autism group displayed inhibitory deficits specifically associated with increasing cognitive load.

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.

An examination of movement kinematics in young people with high-functioning autism and Asperger's disorder: further evidence for a motor planning deficit

This paper examines upper-body movement kinematics in individuals with high-functioning autism (HFA) and Asperger's disorder (AD). In general, the results indicate that HFA is more consistently associated with impaired motoric preparation/initiation than AD. The data further suggest that this quantitative difference in motor impairment is not necessarily underpinned by greater executive dysfunction vulnerability in autism relative to AD. Quantitative motoric dissociation between autism and AD may have down-stream effects on later stages of movement resulting in qualitative differences between these disorder groups, e.g. "motor clumsiness" in AD versus "abnormal posturing" in autism. It will be important for future research to map the developmental trajectory of motor abnormalities in these disorder groups.

Pseudo-random number generation in children with high-functioning autism and Asperger's disorder: further evidence for a dissociation in executive functioning?

The repetitive, stereotyped and obsessive behaviours, which are core diagnostic features of autism, are thought to be underpinned by executive dysfunction. This study examined executive impairment in individuals with autism and Asperger's disorder using a verbal equivalent of an established pseudo-random number generating task. Different patterns of disinhibition emerged in the autism (n = 12) and Asperger's disorder (n = 12) groups. Consistent with previous research, the autism group repeated single numbers (e.g. 2, 2, 2) more frequently than the control group. In contrast to past research suggesting intact executive abilities, this study found that the Asperger's disorder group generated more repetitive number patterns (e.g. 45, 45) than the controls. Executive functioning in children with Asperger's disorder may be particularly vulnerable to a lack of visual cueing and concrete rules. Qualitative differences in executive dysfunction between these groups may implicate differential disruption within the fronto-striatal circuitry.

Autism and Asperger's disorder: Are they movement disorders involving the cerebellum and/or basal ganglia?

Autism and Asperger's disorder (AD) are childhood developmental disorders of unknown aetiology. Autism and AD share several behavioural features, and it is not clear whether they are distinct disorders or variants of the same disorder. Recent studies indicate that disordered movement may be another feature of autism and AD, and that this may reflect dysfunction within the frontostriatal and/or cerebellar motor circuits. While disordered movement in autism and AD has been examined in a variety of ways, it is relatively under-researched compared to the cognitive, affective, and behavioural disturbances seen in these disorders. This review examines the role of the frontostriatal and cerebellar motor systems in the behavioural features of autism and AD, with gait as a proxy, and discusses difficulties with their diagnosis and their possible pathogenesis.

Findings of brain 99mTc-ECD SPECT in high-functioning autism-3-dimensional stereotactic ROI template analysis of brain SPECT-

The aim of this study is confirmation of an abnormal regional cerebral blood flow (rCBF) pattern in high-functioning autism (HFA). Confirmation of an abnormal rCBF pattern in HFA may be useful for elucidate of its pathophysiology and a differential diagnosis, such as with attention-deficit/hyperactivity disorder (AD/HD). Brain 99mTc-ECD SPECT was performed in 16 cases of HFA. The HFA group consisted of 16 cases of HFA. They were all male, with an IQ of 76-126. They had normal brain MRI findings, and had an age of 9-14 years. We examined abnormal rCBF in HFA by comparing the results to those in the control group. The control group consisted of 1 male and 4 females cryptogenic epilepsy patients with normal intelligence. They have no problems in learning at school or mental or behavioral traits. They had normal brain MRI or SPECT findings, and had an age of 7-15 years. 3-dimensional stereotactic ROI template (3DSRT) was used to analyze SPECT data. We calculated the 'relative rCBF (%)' (RI count of each segment x 100/Sum of RI count of the corresponding hemisphere), and compared the values between the two groups. We found a significantly low 'relative rCBF (%)' in the left temporal region in the HFA group. We also calculated the 'L/R ratio' (the 'relative rCBF (%)' of a segment on the left side / the 'relative rCBF (%)' of the corresponding segment on the right side), and compared the value for each segment between the two groups. There were no significant differences in any segments between the two groups. We also checked for differences in the 'relative rCBF (%)' between segments on the right side and corresponding segments on the left side in both the HFA and control groups. We found significant right < left perfusion in the angular region and significant left < right perfusion in the pericallosal, thalamus, and hippocampus region in the HFA group. We also found significant right < left perfusion in the temporal region in the control group. Significant hypoperfusion in the left temporal region due to an unidentified underlying brain pathology and abnormal laterality in the angular, temporal (lack of right < left perfusion), pericallosal, thalamus, and hippocampus regions may influence the symptoms of autism.

Autism

Autism is a neurologic disorder with impairments in language, social communication, and behavior, which may improve over time, but which persist throughout the lifetime. The evaluation of autism requires a separation of clinical and research objectives and is done best in close cooperation with professionals in the fields of communication, education, and psychology. There are no biologic markers of autism. Regression in language and social communication is present in approximately 30% of children with autism and is most likely to occur between 18 and 24 months of age. Early deficits in social communication can be identified by the assessment of joint attention, affective reciprocity, and metacognition. Current evidence suggests that deficits in social cognition and communication in autism may be related to dysfunction in the amygdala, hippocampus, and related limbic and cortical structures. Other neuroanatomic structures, such as the cerebellum, also may form part of a distributed neuronal network responsible for social cognition and communication. Genetics play a major role in autism, but what is inherited and how broad the inheritable phenotype is remain unclear. At a neurochemical level, the principal neurotransmitter implicated in autism is serotonin. Seizures and epileptiform discharges are common in autism and are linked to cognitive dysfunction. The role of medication is to target specific symptoms and open windows of opportunity that allow implementation of a multimodal individualized educational plan.

Behavioral phenotype of the reeler mutant mouse: effects of RELN gene dosage and social isolation

Reeler (rl/rl) and reeler/wild-type (+/rl) mice synthesize Reln at subnormal rates, as do patients with schizophrenia, bipolar disorder, and autism, thereby forming the basis for a Reln hypothesis for vulnerability to these psychopathologies and justifying attention to the behavioral phenotypes of Reln-deficient mice. Tests of gait, emotionality, social aggression, spatial working memory, novel-object detection, fear conditioning, and sensorimotor reflex modulation revealed the behavioral phenotype of rl/rl, but not +/rl, mice to be different from that of wild-type (+/+) mice. These results reveal no effect of Reln gene dosage and provide significant challenges to both the Reln and the neurodevelopmental hypotheses of the etiology of major psychopathologies.

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.

Motor performance and anatomic magnetic resonance imaging (MRI) of the basal ganglia in autism

This study was conducted to examine the volume of the basal ganglia in individuals with autism and to evaluate whether performance on specific motor tasks correlated with the volume of these structures. Volumetric measurements of the caudate nucleus and putamen were obtained from magnetic resonance images (MRI) of 40 non-mentally retarded individuals with autism and 41 healthy controls. Motor performance was assessed in these subjects by using the Finger Tapping Test, the Grooved Pegboard Test, and the measurement of Grip Strength. No volumetric differences of the basal ganglia were found between the two groups after adjusting for brain volume. The autistic subjects' performance was slower on the Grooved Pegboard Test and weaker on Grip Strength. Our findings suggest that the motor deficits observed in autism may not be related to structural abnormalities of the basal ganglia, and other brain regions, such as the cerebellum and the frontal lobe, may be involved in the pathophysiology of motor disturbances in autism.

Lateralization in individuals with high-functioning autism and Asperger's disorder: a frontostriatal model

Neurobiological and behavioural studies of possible left hemisphere dysfunction in autism have generated conflicting results. Left hemisphere dysfunction may manifest in autism only in tasks that invoke executive functions. Moreover, left hemisphere dysfunction may underpin autism but not Asperger's disorder. We thus aimed to systematically investigate reports of anomalous lateralization in individuals with high-functioning autism and Asperger's disorder. Two of the tasks were sensitive to executive dysfunction: a serial choice reaction-time task and a Posner-type paradigm; the remaining tasks instead investigated aspects of perceptual lateralisation. Compared with age- and IQ-matched controls, the autism group displayed deficiencies in right hemispace (and by implication, left hemisphere) performance on both executive function tasks; however, this group demonstrated normal lateralization effects on the nonexecutive, visual-perceptual tasks. In contrast, the Asperger's disorder group showed similar laterality effects to their age- and IQ-matched controls on both executive and nonexecutive function tasks. The etiological relevance of this neurobehavioral dissociation between high-functioning autism and Asperger's disorder was discussed; in particular, it was suggested that the period where dominance shifts from right to left hemisphere is important in whatever process might dictate the emergence of either autism or Asperger's disorder.

The relationship between 99mTc-HMPAO brain SPECT and the scores of real life rating scale in autistic children

Childhood autism is a developmental disability of unknown origin with probable multiple etiologies. The purpose of this study was to compare the changes of regional cerebral blood flow (rCBF) in autistic and non-autistic controls, and to determine the relationship between rCBF on 99mTc-hexamethylpropylene amine oxime (HMPAO) brain SPECT and the scores of the Ritvo-Freeman Real Life Rating Scale (RLRS), IQ levels, and age of autistic children. Eighteen autistic children (four girls, 14 boys; mean age: 6.13 +/- 1.99 years) and 11 non-autistic controls (five girls, six boys, mean age: 6.5 +/- 3.39 years) were examined using 99mTc-HMPAO brain SPECT. All the children satisfying DSM-IV criteria for autistic disorder were taken into evaluation, and scored by the Ritvo-Freeman RLRS. IQ levels of these children were determined by Goodenough IQ test. Six cortical regions of interest (ROIs; frontal (F), parietal (P), frontotemporal (FT), temporal (T), temporo-occipital (TO), and occipital (O)) were obtained on transaxial slices for count data acquisition. The ratio of average counts in each ROI to whole-slice counts for the autistic children was correlated with the scores of Ritvo-Freeman RLRS. Hypoperfusion in rCBF in autistic children compared with the control group were identified in bilateral F, FT, T, and TO regions. We found no relationship between rCBF on 99mTc-HMPAO brain SPECT and the scores of the Ritvo-Freeman RLRS. There was a relationship between bilateral F regions perfusion on 99mTc-HMPAO brain SPECT and the age of autistic children. There was also a negative correlation between IQ levels and the scores of sensory responses, social relationship to people, and sensory-motor responses. Our results suggest that 99mTc-HMPAO brain SPECT is helpful to locate the perfusion abnormalities but no correlation is found between rCBF on 99mTc-HMPAO brain SPECT and the scores of Ritvo-Freeman RLRS.

Obsessive compulsive behaviour in autism--towards an autistic-obsessive compulsive syndrome?

A portion of autistic patients exhibit compulsive-like behaviours. In addition it has been suggested that serotonin plays a major role in both obsessive compulsive disorder (OCD) and autistic disorder. Other neurohumors such as endogenous opioids and oxytocin have also been implicated in the two disorders. There is also some pharmacological overlap between the two disorders, as well as some similar neuroimaging studies. These similarities and overlaps have led us to propose a putative OCD-autistic disorder, which should be studied in greater detail.

Patterns of cortical activity and memory performance in Alzheimer's disease

BACKGROUND

Declarative memory changes are the hallmark of Alzheimer's disease, although their functional neuroanatomy is not restricted to a single structure. Factor analysis provides statistical methods for evaluating patterns of cerebral changes in regional glucose uptake.

METHODS

Thirty-three Alzheimer's patients and 33 age- and gender-matched control subjects were studied with magnetic resonance imaging and positron emission tomography with [(18)F] deoxyglucose. During the tracer-uptake period, subjects performed a serial verbal learning task. Cortical activity was measured in 32 regions of interest, four in each lobe on both hemispheres.

RESULTS

Factor analysis with varimax rotation identified seven factors explaining 80% of the variance ("parietal cortex," "occipital cortex," "right temporo-prefrontal areas," "frontal cortex," "motor strip," "left temporal cortex," and "posterior temporal cortex"). Relative to control subjects, Alzheimer's patients showed significantly reduced values on the factors occipital cortex, right temporo-prefrontal areas, frontal cortex, and left temporal cortex. The factor temporo-prefrontal areas showed large differences between patients with good and poor performance, but little difference when control subjects were similarly divided.

CONCLUSIONS

Findings suggest that Alzheimer's disease is characterized by altered patterns of cortical activity, rather than deficits in a single location, and emphasize the importance of right temporo-prefrontal circuitry for understanding memory deficits.

Movement preparation in high-functioning autism and Asperger disorder: a serial choice reaction time task involving motor reprogramming

Autism and Asperger disorder have long been associated with movement abnormalities, although the neurobehavioural details of these abnormalities remain poorly defined. Clumsiness has traditionally been associated with Asperger disorder but not autism, although this is controversial. Others have suggested that both groups demonstrate a similar global motor delay. In this study we aimed to determine whether movement preparation or movement execution was atypical in these disorders and to describe any differences between autism and Asperger disorder. A simple motor reprogramming task was employed. The results indicated that individuals with autism and Asperger disorder have atypical movement preparation with an intact ability to execute movement. An atypical deficit in motor preparation was found in Asperger disorder, whereas movement preparation was characterized by a "lack of anticipation" in autism. The differences in movement preparation profiles in these disorders were suggested to reflect differential involvement of the fronto-striatal region, in particular the supplementary motor area and anterior cingulate.

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.

Imaging of autism: lessons from the past to guide studies in the future

OBJECTIVE

To review the scientific literature on the imaging of autism with a view to understanding how imaging can contribute to future studies.

METHODS

Medline was searched, and bibliographies from retrieved articles were reviewed. Inclusion criteria were a diagnosis of autism according to Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria, third edition or later, and a control group without autism.

RESULTS

The field suffers from a lack of replication studies and poor methodology in terms of not controlling for confounding variables. Enlarged brain size, particularly in the temporoparietal brain region, and decreased size of the posterior corpus callosum are the only findings that have been independently replicated.

CONCLUSION

Future imaging studies should attempt to investigate more homogeneous subgroups of patients such as those with "the lesser variant of PDD" and high-functioning patients with PDD who do not have comorbid medical conditions. A different approach, examining the individual behaviours that constitute the PDD spectrum and exploring these separately along with other associated variables such as neuropsychological deficits, structural and functional brain abnormalities, and genetic information could help identify biological mechanisms that do not follow diagnostic boundaries.

Brain mapping of language and auditory perception in high-functioning autistic adults: a PET study

We examined the brain organization for language and auditory functions in five high-functioning autistic and five normal adults, using [15O]-water positron emission tomography (PET). Cerebral blood flow was studied for rest, listening to tones, and listening to, repeating, and generating sentences. The autism group (compared to the control group) showed (a) reversed hemispheric dominance during verbal auditory stimulation; (b) a trend towards reduced activation of auditory cortex during acoustic stimulation; and (c) reduced cerebellar activation during nonverbal auditory perception and possibly expressive language. These results are compatible with findings of cerebellar anomalies and may suggest a tendency towards atypical dominance for language in autism.

Age-related shift in brain region activity during successful memory performance

Coregistered positron emission tomography (PET)/magnetic resonance imaging (MRI) was used to characterize brain function in 70 volunteers, aged 20-87 years, during a verbal memory task. Frontal activity showed an age-related decline that remained significant after statistical control for sulcal atrophy. Analyses of young and old subgroups matched for memory scores revealed that young good performers activated frontal regions, whereas old good performers relied on occipital regions. Although activating different cortical regions, good performers of all ages used the same cognitive strategy semantic clustering. Age-related functional change may reflect dynamic re-allocation in a network of brain areas, not merely anatomically fixed neuronal loss or diminished capacity to perform.

Regional cerebral blood flow during the Wisconsin Card Sort Test in schizotypal personality disorder

Regional cerebral blood flow (rCBF) was measured by single photon emission computed tomography in 10 patients with schizotypal personality disorder (SPD) and nine age- and sex-matched normal volunteers. Subjects performed both the Wisconsin Card Sort Test (WCST) and a control task, the Symbol Matching Test (SMT). Four-way analyses of variance were performed to assess relative rCBF of the prefrontal cortex and of the medial temporal region. Normal volunteers showed more marked activation in the precentral gyrus, while SPD patients showed greater activation in the middle frontal gyrus. Relative flow in the left prefrontal cortex was correlated with better WCST performance in normal volunteers. SPD patients, however, showed no such correlations in the left prefrontal cortex, but demonstrated correlations of good and bad performance with CBF in the right middle and inferior frontal gyrus, respectively. Thus, at least some SPD patients demonstrate abnormal patterns of prefrontal activation, perhaps as a compensation for dysfunction in other regions.

Differences in brain metabolites between patients with autism and mental retardation as detected by in vivo localized proton magnetic resonance spectroscopy

We performed volume-selective proton magnetic resonance spectroscopy (1H-MRS) of the brain with a 1.5 T magnet in 28 patients with autism, and compared the results with those from 28 age-matched patients with unclassified mental retardation and 25 age-matched healthy children. Peaks for N-acetylaspartate, choline and creatine, but not lactate, were observed in each group on 1H-MRS. The N-acetylaspartate/choline ratio was lower in patients with mental retardation than in patients with autism and controls (P = .05, respectively). However, there were no differences in the N-acetylaspartate/ choline ratios between patients with autism and controls, and the N-acetylaspartate/creatine and choline/creatine ratios did not differ among the three groups. These results suggest that N-acetylaspartate is decreased in patients with mental retardation and that a disorder or dysfunction of neurons in the brain exists. There also appear to be differences in the brain lesions or dysfunctions found in patients with autism and mental retardation.

Effect of sertraline on regional metabolic rate in patients with affective disorder

Seventeen patients with major affective disorder completed a 10-week, placebo-controlled, randomized trial of the serotonin reuptake inhibitor sertraline. Patients underwent positron emission tomography with 18F-deoxyglucose and were assessed with the Hamilton Depression Rating Scale at baseline and 10 weeks after treatment with sertraline or placebo. The middle frontal gyrus, an area previously characterized by decreased metabolic activity in depressive patients, showed relatively increased activity on both sides after sertraline when contrasted with temporal and some occipital areas. Sertraline was associated with a significantly increased relative metabolic rate in right parietal lobe and in left occipital area 19, and a decreased metabolic rate in right occipital area 18. Other areas that differed between controls and a larger cohort of 39 depressive patients--including medial frontal lobe, cingulate gyrus, and thalamus--also showed a normalization of metabolic rate after sertraline.

Autism: towards an integration of clinical, genetic, neuropsychological, and neurobiological perspectives

Autism constitutes one of the best validated child psychiatric disorders. Empirical research has succeeded in delineating the key clinical phenomena, in demonstrating strong genetic influences on the underlying liability, and in identifying basic cognitive deficits. A range of neurobiological abnormalities has also been found, although the replicability of specific findings has not been high. An understanding of the causal processes leading to autism, and accounting for the marked variability in its manifestations, requires an integration across these different levels of enquiry. Although this is not yet possible, a partial integration provides a useful strategy for identifying key research questions, the limitations of existing hypotheses, and future research directions that are likely to prove fruitful. The research findings for each research level are critically reviewed in order to consider how to move towards an integration across levels.

Glucose metabolic correlates of continuous performance test performance in adults with a history of infantile autism, schizophrenics, and controls

Twenty-five schizophrenic patients, fourteen adults with a history of infantile autism, and twenty normal controls performed a test of sustained attention, the degraded stimulus continuous performance test (CPT), during the 35 minute 18-fluoro-2-deoxyglucose uptake period preceding positron emission tomographic (PET) scan acquisition. This is the first analysis comparing correlations between glucose metabolic rate (GMR) for selected regions and CPT performance. CPT performance differed in controls and schizophrenics, but autistics did not differ from either group. In controls and schizophrenic patients, task performance correlated with GMR in medial superior frontal gyrus and lateral inferior temporal gyrus, suggesting that activation of those regions is important in the normal performance of the task and that damage to those regions, which also showed low GMR in schizophrenics, contributes to the attentional dysfunction in schizophrenia. Also, schizophrenics showed negative correlations of task performance with anterior cingulate activity suggesting that overactivity of that region, which is involved in mental effort and whose GMR was low in our larger study of schizophrenia, impairs task performance in schizophrenics. Autistic patients showed negative correlations of medial frontal cortical GMR with attentional performance, suggesting that neuronal inefficiency in that region may contribute to poor performance.

Patterns of cortical activity in schizophrenia

Eighty-three patients with schizophrenia and 47 healthy controls received positron emission tomography (PET) with 18F-2-deoxyglucose uptake while they were executing the Continuous Performance Test (CPT). The entire cortex was divided into 16 regions of interest in each hemisphere, four in each lobe of the brain, and data from corresponding right and left hemispheric regions were averaged. Data from the schizophrenic patients were subjected to a factor analysis, which revealed five factors that explained 80% of the common variance. According to their content, the factors were identified and labelled 'parietal cortex and motor strip', 'associative areas', 'temporal cortex', 'hypofrontality' (which included midfrontal and occipital areas) and 'frontal cortex'. Hemispheric asymmetry was only confirmed for the temporal cortex. Factor weights obtained in the schizophrenic group were applied to the metabolic data of the healthy controls and factors scales computed. Schizophrenics were significantly more hypofrontal than the controls, with higher values on the 'parietal cortex and motor strip' factor and a trend towards higher values in the temporal cortex. A canonical discriminant analysis confirmed that the 'hypofrontality' and 'parietal cortex and motor strip' factors accurately separated the schizophrenic group from the healthy controls. Hemispheric asymmetry was only confirmed for the temporal lobe. Significantly higher factor scores for the left temporal lobe in schizophrenics than in normals were obtained when calculated for the right and left hemisphere separately. Taken together, our results confirm the importance of hypofrontality as a pattern of cortical metabolic rate and point to the potential importance of parietal and motor strip function in schizophrenia.