Autism is a neurobiological disorder characterized by impairments in reciprocal social skills, as well as verbal and nonverbal language. Odd, repetitive behavior is also one of the defining symptoms of this disorder, says the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (DSM-IV). During the last decade, research into the abnormalities in both brain functions and structure associated with autism has grown tremendously.
Brain Size
Autistic children are born with an average-size head, and thus, an average-size brain. Yet, one to four years later, the circumference of the head in the same test subjects were noted to be considerably larger than normal, according to Dr. Eric Courchesne and his colleagues in the “Journal of American Medical Association” in July 2003. Structural MRI studies confirmed the increase in total brain volume (TBV) in autism suggested by the increase in head circumference. Dr. Diane Williams, in a study published in “Neuroimaging Clinics of North America” in November 2006, stated that magnetic resonance imaging (MRI) studies also confirmed this finding. Her study goes on to report that the abnormal size of the brain seemed to persist into childhood but not into adolescence. Thus, the growth of an autistic brain is initially accelerated but will eventually cease.
Corpus Callosum
An area in the brain that connects the two sides, or hemispheres, of the brain is called the corpus callosum. This area is often smaller in size in the brains of autistic patients, according to Dr. Marcel Adam Just and his colleagues in a study published in the 17th volume of “Cerebral Cortex” in 2007. The authors concluded that communication between certain cortical areas is less effective in autistic patients. The lowered functional connectivity is particularly disruptive to those complex functions that rely heavily on the coordination of brain regions, such as language and problem solving.
Broca's and Wernicke's Areas
Dr. Just and his colleagues studied the brain activation of autistic participants and controls during sentence comprehension by using functional MRI (fMRI). The Wernicke’s area, responsible for understanding language, was much more active in autistic subjects than in controls. On the other hand, Broca’s area, responsible for speech production was less active in autistic participants than in controls. Furthermore, the degree of synchronization between the various participating cortical areas was consistently lower for the autistic than the control participants. From this, the authors concluded that autistic patients do not integrate and synchronize information as effectively as healthy controls during language processing.
References
- American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV); American Psychiatric Association; 1994, Washington DC.
- Journal of American Medical Association:Evidence of Brain Overgrowth in the First Year of Life in Autism
- Neuroimaging Clinics of North America: Understanding Autism and Related Disorders: What Has Imaging Taught Us?
- Cerebral Cortex: Functional and Anatomical Cortical Underconnectivity in Autism
- Brain: Cortical activation and synchronization during sentence comprehension in high-functioning autism
