Neuroscience of Autism

Abstract

Autism is a pervasive developmental disorder characterised by abnormal social–emotional behaviours, repetitive or stereotyped behaviours and delayed or impaired development of language skills. Neuropathological studies have revealed that multiple brain areas are affected in the disorder including the limbic system (hippocampus, amygdala and cingulate cortex), cerebellum, brain stem (inferior olivary nucleus) and parts of the cerebral cortex. There is a decrease in the number of cerebellar Purkinje cells in many individuals with autism. The cerebellum normally functions as an error correction system for fine motor behaviours and has also been implicated in cognitive behaviours. Over the past decade, research has focused on two transmitter systems, serotonin and γ‐aminobutyric acid (GABA). It has been reported that specific types of enzymes and receptors are deficient in individuals with autism. Despite these research findings, effective pharmacotherapies have not yet been developed and treatment outcomes vary.

Key Concepts:

  • Autism is characterised by deficits in social–emotional behaviour, stereotyped or repetitive behaviours and delayed/impaired development of language.

  • Many individuals with autism have decreased numbers of cerebellar Purkinje cells.

  • Neuropathology findings indicate that changes in the brain begin in prenatal development and extend into the postnatal period.

  • Brain overgrowth occurs during the early postnatal period especially in the frontal lobe region in individuals with autism suggesting abnormal connectivity.

  • Consistent results from postmortem studies indicate that in the central nervous system, the inhibitory GABA neurotransmitter system is involved in the disorder.

  • Specific types of GABA, serotonin, acetylcholine and glutamate neurotransmitter receptors appear to be affected in the disorder.

  • Imaging studies have demonstrated that in some brain areas in autistic individuals, differential activation patterns within a particular structure and in laterality.

  • Research efforts are continuing to report interesting findings but no cure or consistent effective treatments have been found.

Keywords: autism; autistic; neuropathology; GABA; serotonin; GAD; limbic system; cerebellum

Figure 1.

Photomicrographs of sections of the cerebellum from a control and an autism case. The cells are stained with a standard Nissl stain (purple) and with calbindin, a calcium‐binding protein that immunostains Purkinje cells (large brown stained cells). In many autism cases, there is a significant decrease in the number of Purkinje cells. From Whitney et al. .

Figure 2.

[3H]‐muscimol labelled GABAA receptor binding in the anterior cingulate cortex in a control case compared to an individual with autism. The red label indicates high binding and the yellow label represents low binding. In the study of 7 adult autism cases and 9 control cases there was a 46.8% reduction in GABAA receptors in the autism cases in the superficial layers (red labelled region) and a 20.2% decrease in the deep cortical layers (yellow labelled region) compared to controls. From Oblak et al. .

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Further Reading

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Blatt, Gene J(Sep 2010) Neuroscience of Autism. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0022369]