Reduced size of corpus callosum in autism

Review of neuroimaging studies of child and adolescent psychiatric disorders from the past 10 years

OBJECTIVES

To review recent neuroimaging studies of serious emotional disorders in youth and identify problems and promise of neuroimaging in clinical practice.

METHOD

Published reports from refereed journals are briefly described, critiqued, and synthesized into a summary of the findings to date.

RESULTS

Childhood-onset schizophrenia shows progressive ventricular enlargement, reduction in total brain and thalamus volume, changes in temporal lobe structures, and reductions in frontal metabolism. Autistic disorder is associated with cerebellar changes, greater total brain and lateral ventricle volume, and asymmetry. The prefrontal cortex and the basal ganglia are consistently reported as abnormal in attention-deficit/hyperactivity disorder. Patients with anorexia nervosa show enlarged CSF spaces and reductions in gray and white matter that are only partially reversible with weight recovery.

CONCLUSIONS

Results from neuroimaging studies of childhood-onset psychiatric disorders suggest consistency in the structures found to be abnormal, but inconsistencies in the nature of these abnormalities. Although neuroimaging technology holds great promise for neurodevelopmental research, it is not yet a diagnostic instrument.

Occurrence of tics in Asperger's syndrome and autistic disorder

Asperger's syndrome is a condition in the autistic spectrum in which language development is normal. Patients with Asperger's syndrome frequently exhibit repetitive movements (stereotypies), and can have motor and phonic tics in addition to other behavioral abnormalities. We present 12 patients with autistic spectrum disorders who were referred to our Movement Disorders Clinic for evaluation of tics. Eight of the 12 had normal language development and therefore met criteria for Asperger's syndrome. All patients exhibited stereotypic movements; in addition, seven had tics and six of these met diagnostic criteria for Tourette syndrome. Of the six patients with clinical features of both Asperger's syndrome and Tourette syndrome, three had severe congenital sensory deficits. The autistic patients in our series were clinically heterogeneous and though tics were clearly present, other aberrant movements demonstrated by them were harder to classify. Our series confirms the wide range of clinical manifestations in Asperger's syndrome and autism, including tics and other features of Tourette syndrome. Furthermore, it suggests that sensory deprivation contributes to the development of adventitious movements in this population.

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.

Magnetic resonance imaging study of the brain in autism

Autism is a neuropsychiatric disorder of social, cognitive, and language development. Cerebellar abnormality in autism has been shown consistently from autopsy and magnetic resonance image (MRI) studies. A new MRI study with careful methodologic designs identified two subgroups of autistic patients: hypoplasia and hyperplasia of cerebellar vermian lobules VI-VII. The existence of these two subtypes was also supported via the meta-analysis of data from separate research groups. In addition to the cerebellar abnormality, recent MRI studies in autism demonstrated abnormalities in the parietal lobe and the posterior subregions of the corpus callosum where parietal cortical fibers are concentrated. Furthermore, neurobehavioral correlates of cerebellar and parietal abnormalities have also been investigated. In contrast, there is a lack of significant difference in the cross-sectional size of the posterior hippocampal formation between autistic and normal subjects, which is discrepant with predictions based on some autopsy studies.

Differential rearing affects corpus callosum size and cognitive function of rhesus monkeys

This study investigated the effects of different rearing conditions on neural and cognitive development of male rhesus monkeys (Macaca mulatta). Infants raised individually in a nursery from 2 to 12 months of age (NURSERY, n=9) were compared to age-matched infants raised in a semi-naturalistic, social environment (CONTROL, n=11). Various brain regions were measured by MRI. Although overall brain volumes did not differ between NURSERY and CONTROL animals, corpus callosum (CC) size, measured in mid-sagittal sections, was significantly decreased in the NURSERY group. Group differences were most evident in the posterior aspects of the corpus callosum and appeared to result from changes in the number of cross-hemispheric projections rather than from a decrease in cortical gray matter volume. The decrease in corpus callosum size in the NURSERY animals persisted after 6 months of social housing in a peer-group. Rearing group differences were not found in other structures analyzed, including the hippocampus, cerebellum and anterior commissure. In cognitive testing, NURSERY animals had more difficulty acquiring the delayed non-matching to sample (DNMS) task, but showed no deficits in subsequent memory performance when a 2 or 10 min delay was imposed. The NURSERY infant monkeys were also impaired in object, but not in spatial, reversal learning, although there were no differences in a simple object discrimination task. The cognitive deficits exhibited by the NURSERY animals were significantly correlated with the alterations found in the CC. In summary, rearing environment was associated with sustained differences in cross-hemispheric projections, white matter volume and cognitive performance.

An animal model of autism: behavioural studies in the GS guinea-pig

Autism is a human behavioural pathology marked by major difficulties in abnormal socialization, language comprehension and stereotypic motor patterns. These behavioural abnormalities have been associated with corticocerebral and cerebellar abnormalities in autistic patients, particularly in vermal folia VI and VII. Progress in understanding this disease has been hindered by the absence of a non-primate animal model. GS guinea-pigs are a partially inbred, non-ataxic guinea-pig strain with cerebellar and corticocerebral abnormalities similar to those reported to exist in human patients with autism. In order to determine if GS guinea-pigs represent an animal model of autism, their behaviour was compared with that of Hartley strain guinea-pigs. GS animals learned a motor task significantly more rapidly than Hartley guinea-pigs, but performed it in a more stereotypic manner and were less influenced by environmental stimuli than Hartleys. GS animals exhibited significantly less exploratory behaviour in a novel environment and were significantly less responsive to 50-95 dBA pure tones than Hartley guinea-pigs. In a social interaction assay, GS guinea-pigs interacted significantly less frequently with each other or with Hartley guinea-pigs than Hartleys did under the same conditions. GS behaviour thus exhibits autistic-like behaviour patterns: motor stereotypy, lack of exploration and response to environment and poor social interaction. Coupled with the neuropathological findings, this abnormal behaviour suggests that GS guinea-pigs could be a useful animal model of autism.

The biological basis of autism

Stimulated by recent advances in genetics and neurobiology, there has been a rapid expansion of studies aimed at elucidating the biological basis of autism. Molecular genetic studies looking for susceptibility genes in this disorder are currently being conducted, and neuroimaging studies attempting to identify characteristic structural and functional brain abnormalities are under way. The results of these studies are likely to have a significant impact on our understanding of the pathogenesis of autism.

Midsagittal corpus callosum area, intelligence, and language dominance in epilepsy

Alterations in midsagittal corpus callosum (CC) area and morphology have been suggested in several disease processes of the nervous system. In addition, some studies found a relation of CC area to handedness, language dominance, and gender. The relation of CC area to measures of intelligence and memory and the effect of epilepsy on CC area have received less attention. In this study CC area was measured on midsagittal magnetic resonance images in 48 patients undergoing presurgical evaluation of epilepsy and in 20 control subjects. All patients had the Wada test and formal neuropsychological testing. The mean CC area of the epilepsy group was significantly smaller than that of control subjects (p < 0.00001). CC area showed a positive correlation with presurgical performance IQ (p = 0.008) and full-scale IQ (p = 0.048), but not with memory scores or language dominance. There was no relation of CC area to location of epileptic focus, seizure types, age at onset, epilepsy duration, or etiology. The presence of an atrophic lesion was associated with a smaller CC area. The correlation of total CC area with performance and full-scale IQs may reflect axonal loss in patients with a low IQ resulting from the etiology of epilepsy or the epilepsy itself.

Neurologic abnormalities in infantile autism

Neuroanatomic, pathologic, and neurobehavioral studies point to a cerebellar and parietal abnormality in autism. We used a standardized protocol to examine neurologic function in 28 pediatric autistic subjects and 24 pediatric normal healthy volunteer controls. As a group, the autistic subjects had quantitative measures from magnetic resonance imaging suggesting hypoplasia or hyperplasia of the cerebellar vermis, as well as measurements of posterior corpus callosum suggesting abnormalities of posterior cortex. In groups of tests that reflect cerebellar and parietal function, the neurologic abnormalities detectable by clinical examination were significantly greater for autistic subjects than for normal controls. These studies confirm that the structural and behavioral deficit in autism does lead to abnormalities that can be detected on the clinical neurologic examination.