Human Brain Imaging of Autism Spectrum Disorders

Autism spectrum disorders include a heterogeneous collection of conditions characterized by the syndrome of autism, namely, marked impairments in social interaction and communication and a markedly restricted and peculiar range of interests and activities. Neuroscience research on autism spectrum disorders is hindered by various different definitions utilized by contributors over the past century. Currently, the criteria for autism spectrum disorders are in flux; new diagnostic requirements for autism spectrum disorders have just been promulgated. Autism spectrum disorders include autistic disorder, Asperger syndrome, Heller syndrome, Rett syndrome, fragile X syndrome, and pervasive developmental disorders. The Rett syndrome is associated with mutations in the X-linked methyl-CpG-binding protein 2 located at the Xq28 region. Fragile X syndrome is associated with abnormalities in the X chromosome. With the exception of the Rett syndrome and the fragile X syndrome, there are likely multiple etiologies for the other autism spectrum disorders. Thus, autism spectrum disorders likely include conditions with disparate biological causes.Human brain imaging includes a spectrum of tools to identify both the structure and the function of the human nervous system utilizing a variety of energy sources and detection modalities. Anomalies in the physiology of the frontal and temporal lobes characterize subgroups of people with autism spectrum disorders. Dysfunction of the frontal and temporal lobes likely provides a pathophysiological basis for the social and language deficits characteristic of the disorders. Dysfunction of the serotonergic and cholinergic systems has been identified in subgroups of people with autism spectrum disorders to support the hypotheses that these systems play a role in the pathophysiology of autism spectrum disorders.Conflicting and contradictory results from reports on human brain imaging of autism spectrum disorders likely stem from the differences in the diagnostic tools, imaging procedures, participant populations, and other characteristics of individual investigations. Additionally, the small sample sizes employed in many imaging studies lack the power to establish a statistical significance.Future research to investigate the brain imaging of humans with autism spectrum disorders can be facilitated by the utilization of accurate diagnostic criteria and rating instruments. Additionally, the identification of demographic, educational, psychiatric, psychological, and neurological characteristics may help to classify people with autism spectrum disorders according to useful clinical groups. Investigation of genetic markers for particular neurotransmitters likely altered in autism spectrum disorders may lead to the discovery of genetic mutations characteristic of subgroups. Careful research including the spectrum of investigative tools will likely result in the identification of biological markers to identify distinct groups such as the Rett syndrome and fragile X syndrome.