Brainstem involvement in high functioning autistic children

Differential volume reductions in the subcortical, limbic, and brainstem structures associated with behavior in Prader-Willi syndrome

Individuals with Prader-Willi syndrome (PWS) exhibit complex behavioral characteristics, including hyperphagia, autistic features, and subsequent age-related maladaptive behaviors. While this suggests functional involvements of subcortical, limbic, and brainstem areas, developmental abnormalities in such structures remain to be investigated systematically. Twenty-one Japanese individuals with PWS and 32 healthy controls with typical development were included. T₁-weighted three-dimensional structural magnetic resonance images were analyzed for subcortical, limbic, and brainstem structural volumes, with age as a covariate, using a model-based automatic segmentation tool. Correlations were determined between each volume measurement and behavioral characteristics as indexed by questionnaires and block test scores for hyperphagia (HQ), autistic and obsessional traits, non-verbal intelligence (IQ), and maladaptive behavior (VABS_mal). Compared with the control group, the PWS group showed significantly reduced relative volume ratios per total intracranial volume (TIV) in thalamus, amygdala, and brainstem structures, along with TIV and native volumes in all substructures. While the brainstem volume ratio was significantly lower in all age ranges, amygdala volume ratios were significantly lower during early adulthood and negatively correlated to HQ and VABS_mal but positively correlated to Kohs IQ. Thus, limbic and brainstem volume alterations and differential volume trajectories may contribute to the developmental and behavioral pathophysiology of PWS.

A Systematic Review of Brainstem Contributions to Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that affects one in 66 children in Canada. The contributions of changes in the cortex and cerebellum to autism have been studied for decades. However, our understanding of brainstem contributions has only started to emerge more recently. Disruptions of sensory processing, startle response, sensory filtering, sensorimotor gating, multisensory integration and sleep are all features of ASD and are processes in which the brainstem is involved. In addition, preliminary research into brainstem contribution emphasizes the importance of the developmental timeline rather than just the mature brainstem. Therefore, the purpose of this systematic review is to compile histological, behavioral, neuroimaging, and electrophysiological evidence from human and animal studies about brainstem contributions and their functional implications in autism. Moreover, due to the developmental nature of autism, the review pays attention to the atypical brainstem development and compares findings based on age. Overall, there is evidence of an important role of brainstem disruptions in ASD, but there is still the need to examine the brainstem across the life span, from infancy to adulthood which could lead the way for early diagnosis and possibly treatment of ASD.

Central Auditory and Vestibular Dysfunction Are Key Features of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by repetitive behaviors, poor social skills, and difficulties with communication. Beyond these core signs and symptoms, the majority of subjects with ASD have some degree of auditory and vestibular dysfunction. Dysfunction in these sensory modalities is significant as normal cognitive development depends on an accurate representation of our environment. The hearing difficulties in ASD range from deafness to hypersensitivity and subjects with ASD have abnormal sound-evoked brainstem reflexes and brainstem auditory evoked potentials. Vestibular dysfunction in ASD includes postural instability, gait dysfunction, and impaired gaze. Untreated vestibular dysfunction in children can lead to delayed milestones such as sitting and walking and poor motor coordination later in life. Histopathological studies have revealed that subjects with ASD have significantly fewer neurons in the auditory hindbrain and surviving neurons are smaller and dysmorphic. These findings are consistent with auditory dysfunction. Further, the cerebellum was one of the first brain structures implicated in ASD and studies have revealed loss of Purkinje cells and the presence of ectopic neurons. Together, these studies suggest that normal auditory and vestibular function play major roles in the development of language and social abilities, and dysfunction in these systems may contribute to the core symptoms of ASD. Further, auditory and vestibular dysfunction in children may be overlooked or attributed to other neurodevelopmental disorders. Herein we review the literature on auditory and vestibular dysfunction in ASD. Based on these results we developed a brainstem model of central auditory and vestibular dysfunction in ASD and propose that simple, non-invasive but quantitative testing of hearing and vestibular function be added to newborn screening protocols.

Evidence for Brainstem Contributions to Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental condition that affects one in 59 children in the United States. Although there is a mounting body of knowledge of cortical and cerebellar contributions to ASD, our knowledge about the early developing brainstem in ASD is only beginning to accumulate. Understanding how brainstem neurotransmission is implicated in ASD is important because many of this condition’s sensory and motor symptoms are consistent with brainstem pathology. Therefore, the purpose of this review was to integrate epidemiological, behavioral, histological, neuroimaging, and animal evidence of brainstem contributions to ASD. Because ASD is a neurodevelopmental condition, we examined the available data through a lens of hierarchical brain development. The review of the literature suggests that developmental alterations of the brainstem could have potential cascading effects on cortical and cerebellar formation, ultimately leading to ASD symptoms. This view is supported by human epidemiology findings and data from animal models of ASD, showing that perturbed development of the brainstem substructures, particularly during the peak formation of the brainstem’s monoaminergic centers, may relate to ASD or ASD-like behaviors. Furthermore, we review evidence from human histology, psychophysiology, and neuroimaging suggesting that brainstem development and maturation may be atypical in ASD and may be related to key ASD symptoms, such as atypical sensorimotor features and social responsiveness. From this review there emerges the need of future research to validate early detection of the brainstem-based somatosensory and psychophysiological behaviors that emerge in infancy, and to examine the brainstem across the life span, while accounting for age. In all, there is preliminary evidence for brainstem involvement in ASD, but a better understanding of the brainstem’s role would likely pave the way for earlier diagnosis and treatment of ASD.

Variant in oxytocin receptor gene is associated with amygdala volume

The oxytocin system plays a significant role in modulating stress responses in animals and humans; perturbations in this system may contribute to the pathogenesis of psychiatric disorder. Attempts to identify clinically relevant genetic variants in the oxytocin system have yielded associations between polymorphisms of the oxytocin receptor (OXTR) gene and both autism and major depression. To date, however, little is known about how such variants affect brain structures implicated in these disorders. Applying a manual tracing procedure to high-resolution structural magnetic resonance images, amygdala volumes were measured in 51 girls genotyped on OXTR rs2254298(G>A), a single nucleotide polymorphism associated with psychopathology. Results of this study indicate that despite having greater gray matter volume, participants homozygous for the G allele were characterized by smaller volumes of both left and right amygdala than were carriers of the A allele. A subsequent whole-brain voxel-based morphometry analysis revealed additional genotype-mediated volumetric group differences in the posterior brain stem and dorsomedial anterior cingulate cortex. These findings highlight one neurobiological pathway by which oxytocin gene variants may increase risk for psychopathology. Further research is needed to characterize the mechanism by which this polymorphism contributes to anatomical variability and to identify functional correlates of these alterations in regional brain volume.

Abnormal auditory forward masking pattern in the brainstem response of individuals with Asperger syndrome

Abnormal auditory information processing has been reported in individuals with autism spectrum disorders (ASD). In the present study auditory processing was investigated by recording auditory brainstem responses (ABRs) elicited by forward masking in adults diagnosed with Asperger syndrome (AS). Sixteen AS subjects were included in the forward masking experiment and compared to three control groups consisting of healthy individuals (n = 16), schizophrenic patients (n = 16) and attention deficit hyperactivity disorder patients (n = 16), respectively, of matching age and gender. The results showed that the AS subjects exhibited abnormally low activity in the early part of their ABRs that distinctly separated them from the three control groups. Specifically, wave III amplitudes were significantly lower in the AS group than for all the control groups in the forward masking condition (P < 0.005), which was not the case in the baseline condition. Thus, electrophysiological measurements of ABRs to complex sound stimuli (eg, forward masking) may lead to a better understanding of the underlying neurophysiology of AS. Future studies may further point to specific ABR characteristics in AS individuals that separate them from individuals diagnosed with other neurodevelopmental diseases.

Reduced gyral window and corpus callosum size in autism: possible macroscopic correlates of a minicolumnopathy

Minicolumnar changes that generalize throughout a significant portion of the cortex have macroscopic structural correlates that may be visualized with modern structural neuroimaging techniques. In magnetic resonance images (MRIs) of fourteen autistic patients and 28 controls, the present study found macroscopic morphological correlates to recent neuropathological findings suggesting a minicolumnopathy in autism. Autistic patients manifested a significant reduction in the aperture for afferent/efferent cortical connections, i.e., gyral window. Furthermore, the size of the gyral window directly correlated to the size of the corpus callosum. A reduced gyral window constrains the possible size of projection fibers and biases connectivity towards shorter corticocortical fibers at the expense of longer association/commisural fibers. The findings may help explain abnormalities in motor skill development, differences in postnatal brain growth, and the regression of acquired functions observed in some autistic patients.

Deficient brainstem encoding of pitch in children with Autism Spectrum Disorders

OBJECTIVE

Deficient prosody is a hallmark of the pragmatic (socially contextualized) language impairment in Autism Spectrum Disorders (ASD). Prosody communicates emotion and intention and is conveyed through acoustic cues such as pitch contour. Thus, the objective of this study was to examine the subcortical representations of prosodic speech in children with ASD.

METHODS

Using passively evoked brainstem responses to speech syllables with descending and ascending pitch contours, we examined sensory encoding of pitch in children with ASD who had normal intelligence and hearing and were age-matched with typically developing (TD) control children.

RESULTS

We found that some children on the autism spectrum show deficient pitch tracking (evidenced by increased Frequency and Slope Errors and reduced phase locking) compared with TD children.

CONCLUSIONS

This is the first demonstration of subcortical involvement in prosody encoding deficits in this population of children.

SIGNIFICANCE

Our findings may have implications for diagnostic and remediation strategies in a subset of children with ASD and open up an avenue for future investigations.

Quantitative magnetic resonance image analysis of the cerebellum in macrocephalic and normocephalic children and adults with autism

A detailed morphometric analysis of the cerebellum in autism with and without macrocephaly. Four subject groups (N = 65; male; IQs > or = 65; age 7 to 26 years) were studied with quantitative MRI; normocephalic and macrocephalic individuals with autism without mental retardation were compared to normocephalic and benign macrocephalic typically developing individuals. Total cerebellum volumes and surface areas of four lobular midsagittal groups were measured. Independent t-tests between autism and control subjects matched for head size revealed no significant differences. Multivariate analyses of variance were also performed, using the diagnostic group as the fixed factor, cerebellar measures as the dependent variables and total intracranial volume, total brain volume, age, verbal IQ, and performance IQ as covariates. No significant differences were found; however, a trend was noted in which macrocephalic individuals with autism consistently exhibited slightly smaller cerebellar volume or surface area when compared to individuals with benign macrocephaly. In autism, with and without macrocephaly, cerebellar structures were found to be proportional to head size and did not differ from typically developing subjects.

Neurobiological correlates of autism: a review of recent research

This review paper integrates recent structural and functional imaging, postmortem, animal lesion, and neurochemical research about the pathophysiology of autism. An understanding of the neurobiological correlates of autism is becoming increasingly important as more children are diagnosed with the condition and funding for well-targeted interventions increases. Converging evidence suggests that autism involves abnormalities in brain volume, neurotransmitter systems, and neuronal growth. In addition, evidence firmly links autism with abnormalities in the cerebellum, the medial temporal lobe, and the frontal lobe. Potential implications of these findings and suggestions for future research are reviewed.

Goal directed locomotion and balance control in autistic children

This article focuses on postural anticipation and multi-joint coordination during locomotion in healthy and autistic children. Three questions were addressed. (1) Are gait parameters modified in autistic children? (2) Is equilibrium control affected in autistic children? (3) Is locomotion adjusted to the experimenter-imposed goal? Six healthy children and nine autistic children were instructed to walk to a location (a child-sized playhouse) inside the psychomotor room of the pedopsychiatric centre located approximately 5 m in front of them. A kinematic analysis of gait (ELITE system) indicates that, rather than gait parameters or balance control, the main components affected in autistic children during locomotion are the goal of the action, the orientation towards this goal and the definition of the trajectory due probably to an impairment of movement planning.

Imaging data in autism: from structure to malfunction

During the last two decades, neuroimaging studies have improved our knowledge of brain development and contributed to our understanding of disorders involving the developing brain. Differences in cerebral anatomy have been determined in autism spectrum disorder (ASD). Morphological studies by magnetic resonance imaging have provided evidence of structural differences in ASD compared with the normal population. This has enhanced our view of autism as a neurobiological disorder corresponding with different stages and events in brain development. Alterations in volume of the total brain and specifically the cerebellum, frontal lobe, and limbic system have been identified. There appears to be a pattern of increased and then decreased rate of brain growth over time. We integrate these observations with neurobehavioral findings to provide a developmental hypothesis of the pathophysiology of autism.

Autism and pervasive developmental disorders

The quantity and quality of research into autism and related conditions have increased dramatically in recent years. Consequently we selectively review key accomplishments and highlight directions for future research. More consistent approaches to diagnosis and more rigorous assessment methods have significantly advanced research, although the boundaries of the 'broader phenotype' remain to be defined and the validity of Asperger's disorder as a discrete syndrome remains controversial. Recent epidemiological studies have shown that Autism Spectrum Disorders are common, but there continues to be debate about the causes of the increase in the frequency with which autism is diagnosed. Psychological research has helped to develop new developmental models for the disorder and there have also been significant advances in the molecular genetics of autism and understanding of the underlying neurobiological processes. Areas important for future research include the study of autism as it first develops, i.e., in infants and very young children, and of specific processes (psychological and neurobiological) which underlie the disorder. Significant challenges lie ahead in evaluating the growing number of treatments for autism and in integrating the results of research into treatment and educational settings.

Magnetic resonance imaging studies on autism and childhood-onset schizophrenia in children and adolescents - a review

OBJECTIVE

To find out whether the neurodevelopmental disorders autism and childhood-onset schizophrenia have a common developmental pathway and whether the abnormalities detected are 'disorder-specific', by reviewing magnetic resonance imaging (MRI) studies.

METHODS

As a result of a Medline search, we were able to access 28 studies on autism and 12 studies on childhood-onset schizophrenia, which focused on children and adolescents.

RESULTS

Larger lateral ventricles were found to be a common abnormality in both disorders. 'Disorder-specific' abnormalities in patients with autism were larger brains, a larger thalamic area, and a smaller right cingulate gyrus. Subjects with childhood-onset schizophrenia were found to have smaller brains, a smaller amygdalum and thalamus, and a larger nucleus caudatus. In subjects with childhood-onset schizophrenia, abnormalities appeared to progress over a limited period of time.

CONCLUSIONS

Because the study designs varied so much, the results should be interpreted cautiously. Before abnormalities found in the disorders can be designated as equal or 'disorder-specific', it will be essential to perform large longitudinal and cross-sectional follow-up studies.

Structural and functional magnetic resonance imaging of autism

Magnetic resonance imaging (MRI) of brain structures and function is uniquely suited to characterize the range of neuroanatomical and physiological changes that characterize the autism phenotype as it develops over time. In this review, we examine the scientific literature in MRI as applied to autism and related areas, over approximately the last decade, discussing findings which have emerged, methodological stumbling blocks which have been identified, and potential future directions. Structural MRI studies have recently begun to elucidate the neurodevelopmental underpinnings and brain-behavior relationships in autism while fMRI studies, building on the wealth of data in normal individuals, are beginning to characterize the underlying neuropsychological deficits of the disorder. Together, these two methods combine to contribute to a better understanding of the neural basis and brain phenotype of this disorder.

Posterior fossa magnetic resonance imaging in autism

OBJECTIVE

To determine whether the sizes and volumes of the posterior fossa structures are abnormal in non-mentally retarded autistic adolescents and adults.

METHOD

Volume measurements of the cerebellum, vermis, and brainstem were obtained from coronal magnetic resonance imaging scans in 16 autistic subjects and 19 group-matched healthy controls. For the purpose of comparison with previous studies, area measurements of the midbrain, pons, medulla, total cerebellar vermis, and its three subregions were also obtained from a larger sample of 22 autistic males (mean age: 22.4 years; range: 12.2-51.8 years) and 22 individually matched controls (mean age 22.4 years; range: 12.9-52.2 years).

RESULTS

The total volume of the cerebellum and the cerebellar hemispheres were significantly larger in the autistic subjects with and without correcting for total brain volume. Volumes of the vermis and the brainstem and all area measurements did not differ significantly between groups.

CONCLUSIONS

There is an increase in the volume of the cerebellum in people with autism consistent with the increase in regional and total brain size reported in this developmental disorder. This finding is also concordant with evidence of cerebellar abnormalities from neuropathological and neuropsychological studies that point to the role of this structure, as part of a complex neural system, in the pathophysiology of autism.

Evidence of normal cerebellar control of the vestibulo-ocular reflex (VOR) in children with high-functioning autism

The effect of "tilt-suppression" on post-rotatory vestibular nystagmus was investigated to assess the function of the caudal cerebellar vermis (lobules IX and X, or nodulus and uvula) in 13 school-age children with high-functioning autism (HFA) and 10 normal controls. Tilt-suppression of the vestibulo-ocular reflex (VOR) refers to the decreasing of the duration of post-rotatory vestibular nystagmus that occurs when the head is moved out of the plane in which it was located during the previous sustained constant-velocity rotation. The participant is rotated in a vestibular chair with the head upright and then the head is tilted forward just after the chair stops rotating. Such tilt-suppression is impaired with lesions of the cerebellar nodulus and portions of the uvula. Results show that children with HFA have normal post-rotatory nystasmus with the head upright and normal attenuation of post-rotatory nystagmus induced by head tilt. These behavioral findings suggest that lobules IX and X of the cerebellum are spared in high-functioning autism.

Regulation of retinoic acid signaling in the embryonic nervous system: a master differentiation factor

This review describes some of the properties of retinoic acid (RA) in its functions as a locally synthesized differentiation factor for the developing nervous system. The emphasis is on the characterization of the metabolic enzymes that synthesize and inactivate RA, and which determine local RA concentrations. These enzymes create regions of autocrine and paracrine RA signaling in the embryo. One mechanism by which RA can act as a differentiation agent is through the induction of growth factors and their receptors. Induction of growth factor receptors in neural progenitor cells can lead to growth factor dependency, and the consequent developmental fate of the cell will depend on the local availability of growth factors. Because RA activates the early events of cell differentiation, which then induce context-specific differentiation programs, RA may be called a master differentiation factor.

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.

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.

Understanding developmental psychopathology: how useful are evolutionary accounts?

OBJECTIVE

To consider the power of principles derived from evolutionary biology to explain the causes and determinants of some forms of child and adolescent mental disorders.

METHOD

The authors reviewed the scientific literature for evolutionary mechanisms proposed to contribute to the pathogenesis of early-onset disorders.

RESULTS

A diverse set of evolutionary mechanisms has been proposed. With the exception of certain genetically determined conditions, many of the proposed mechanisms have little empirical data to support them. One mechanism focuses on the vulnerabilities associated with conserved behavior patterns, such as separation anxiety and other alarm responses. These behavioral patterns are adaptive if they appear in some situations, but not in others. Other attractive theories include a co-optation of underlying neurobiology systems (substance abuse), environmental shifts (transformation of present day environments away from primeval environments), and evolutionary arms races as may occur in putative autoimmune disorders with neuropsychiatric sequelae.

CONCLUSIONS

Evolutionary biology provides a potentially powerful framework for understanding disease pathogenesis in child psychiatry and should permit the integration of new knowledge from a broad range of scientific disciplines. Evolutionary explanations are typically population-based and fail to account for why a particular individual is disciplines. Evolutionary explanations are typically population-based and fail to account for why a particular individual is affected. Consequently, any adequate account of disease pathogenesis requires that environmental events that impinge on CNS development be considered. Finally, the empirical testing of specific theories may prove to be difficult if not impossible.

Development of the brainstem and cerebellum in autistic patients

Studies of magnetic resonance images have revealed morphological disorders of the brainstem and cerebellum in autistic children and adults. When we studied development of the brainstem and cerebellum in autistic patients, we found that although the brainstem and cerebellum significantly increased in size with age in both autistic patients and controls, these structures were significantly smaller in autistic patients than in controls. The speed of development of the pons, the cerebellar vermis I-V and the cerebellar vermis VI-VII was significantly more rapid in autistic patients than in the controls. However, the speed of development of the other brain structures in the posterior fossa did not differ between autistic patients and controls. The regression intercepts of the brainstem and cerebellum as well as those of their components were significantly smaller in autistic patients than in controls. Results suggest that brainstem and vermian abnormalities in autism were due to an early insult and hypoplasia rather than to a progressive degenerative process.