Anatomical Brain Defects A Multiple Anatomical Abnormalities

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Among all types of biological abnormalities in autism, evidence for neuroanatomical abnormality is the strongest. Studies show that in autism, most major brain structures are affected (Fig. 6); these include the cerebellum, cerebrum, limbic system, corpus callosum, basal ganglia, and brain stem. Recent evidence shows that within the cerebellum and cerebrum, there is abnormality in white and gray matter. Such widespread anatomic abnormality explains why autism involves pervasive and persistent neurological and behavioral dysfunction.

Among all anatomic findings, the most consistent is abnormality in the cerebellum. According to MRI data on large numbers of autistic children and adults, there is a reduction in the size of the neocerebellar vermis and the volume of cerebellar cortex. Also in autistic children, there is an inverse relationship between the size of the cerebellar vermis lobules VI and VII and the size of frontal lobes, such that the smaller the vermis, the larger the frontal lobes. In brain autopsy studies, 90% of autistic cases have reduced numbers of Purkinje neurons in the cerebellar vermis and cerebel-lar hemispheres. The amount of loss typically ranges from about 20 to 60% across different autistic individuals, but in one autistic case Purkinje neuron loss was nearly total throughout the cerebellar hemispheres. Also, Purkinje neuron loss is patchy, and the distribution across the cerebellar hemispheres and vermis differs between individual autistic cases. Autopsy studies have also reported other types of cerebellar anatomic abnormality in other autistic cases. Therefore, cerebellar anatomic abnormality is present in 95% of all autism autopsy cases, making this the most common biological abnormality known for this disorder (Fig. 7).

The limbic system is another common site of anatomic abnormality. In living autistic patients, the amygdala has a reduced volume and the dentate gyrus has a reduced cross-sectional area. In autopsy studies, anatomic abnormality in limbic structures is present in most, but not all, autism cases. When present, limbic system abnormality involves increased density of neurons and reduction in neuron sizes.

Another important site is the cerebrum. A recent MRI study found abnormally increased volume of the

Autopsy Autistic Brain

Figure 6 Depiction of cortical and subcortical structures reported as abnormal in autism via autopsy or MRI data from laboratories throughout the United States and Europe. 1, frontal lobes; 2, parietal lobes; 3, cerebellum; 4, brain stem; 5, corpus callosum; 6, basal ganglia; 7, hippocampus; 8, amygdala. (See color insert).

Figure 6 Depiction of cortical and subcortical structures reported as abnormal in autism via autopsy or MRI data from laboratories throughout the United States and Europe. 1, frontal lobes; 2, parietal lobes; 3, cerebellum; 4, brain stem; 5, corpus callosum; 6, basal ganglia; 7, hippocampus; 8, amygdala. (See color insert).

Boy without CNS pathology

Boy without CNS pathology

Subcortical Structures Color

Figure 7 In autism, reduction in cerebellar Purkinje neuron numbers is a common finding across postmortem cases examined to date. (Top) Control case; (Bottom) autism case. Figure shows a comparable span of cerebellar cortex in a control case and in a case with autism. Arrows point to Purkinje cell bodies in these Nissel-stained sections. There also appear to be fewer granule neurons in the case with autism [adapted with permission from Ritvo, E. R., Freeman, B. J., and Scheibel, A. B. (1986). Lower Purkinje cell counts in the cerebella of four autistic subjects: Initial findings of the UCLA-NSAC autopsy research report. Am. J. Psychiatry 143, 862-866.]

Figure 7 In autism, reduction in cerebellar Purkinje neuron numbers is a common finding across postmortem cases examined to date. (Top) Control case; (Bottom) autism case. Figure shows a comparable span of cerebellar cortex in a control case and in a case with autism. Arrows point to Purkinje cell bodies in these Nissel-stained sections. There also appear to be fewer granule neurons in the case with autism [adapted with permission from Ritvo, E. R., Freeman, B. J., and Scheibel, A. B. (1986). Lower Purkinje cell counts in the cerebella of four autistic subjects: Initial findings of the UCLA-NSAC autopsy research report. Am. J. Psychiatry 143, 862-866.]

cerebrum, but only in 2- to 4-year-old autistic children. A follow-up study found a gradient of abnormality in these very young autistic children, such that abnormal increases in volume were most marked in frontal brain regions and least in posterior regions. In autopsy studies, some autistic patients have abnormally increased thickness of frontal cortical regions; however, other autistic patients have irregular formation of the layers of cortical regions. The corpus callosum is a massive tract of fibers enabling communication between the right and left hemispheres of the cerebrum, and in the posterior portion of it there is a reduction in size.

Anatomic abnormalities in some sites have only been reported from single MRI studies (e.g., parietal lobe and basal ganglia) or in single individuals at postmortem (e.g., superior olive agenesis and facial motor nucleus dysgenesis); how common these sites of abnormality are remains unknown.

In conclusion, anatomical abnormalities in the autistic brain prove that this is a biological disorder, not a psychogenic one. Different brain structures have different types of abnormality (e.g., cerebellum and cerebrum), and even within a particular brain structure (e.g., frontal cortex) more than one type of abnormality can be seen in different autistic patients. Also, among patients with the same type of anatomic defect, there are differences in the amount and exact location of abnormality. Such individual-specific differences in anatomic abnormality in the cerebellum, limbic sys tem, cerebrum, and so forth may be the reason for individual differences in initial symptoms and behavioral outcome.

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Funny Wiring Autism

Funny Wiring Autism

Autism is a developmental disorder that manifests itself in early childhood and affects the functioning of the brain, primarily in the areas of social interaction and communication. Children with autism look like other children but do not play or behave like other children. They must struggle daily to cope and connect with the world around them.

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