Much like a computer, the brain relies on intricate wiring to process and transmit information. Scientists have discovered that in people with autism, this wiring is faulty, leading to misfiring in communications between brain cells.
In the brain, nerve cells transmit important messages that regulate body functions -- everything from social behavior to movement. Imaging studies have revealed that autistic children have too many nerve fibers, but that they're not working well enough to facilitate communication between the various parts of the brain. Scientists think that all of this extra circuitry may affect brain size. Although autistic children are born with normal or smaller-than-normal brains, they undergo a period of rapid growth between ages 6 and 14 months, so that by about age four, their brains tends to be unusually large for their age. Genetic defects in brain growth factors may lead to this abnormal brain development.
Scientists also have discovered irregularities in the brain structures themselves, such as in the corpus callosum (which facilitates communication between the two hemispheres of the brain), amygdala (which affects emotion and social behavior), and cerebellum (which is involved with motor activity, balance, and coordination). They believe these abnormalities occur during prenatal development.
In addition, scientists have noted imbalances in neurotransmitters -- chemicals that help nerve cells communicate with one another. Two of the neurotransmitters that appear to be affected are serotonin (which affects emotion and behavior) and glutamate (which plays a role in neuron activity). Together, these brain differences may account for autistic behaviors.
Scientists continue to look for clues to the origins of autism. By studying the genetic and environmental factors that may cause the condition, they hope to develop tests to identify autism earlier, as well as new treatment methods.
Several research studies are looking at the link between genes and autism. The largest of these is the National Alliance for Autism Research (NAAR) Autism Genome Project. This collaborative effort, conducted at approximately 50 research institutions in 19 countries, is poring through the 30,000 genes that make up the human genome in a search for the genes that trigger autism.
Other autism studies include:
- Using animal brain models to study how neurotransmitters are impaired in children with autism
- Testing a computer-based program that would help autistic children interpret facial expressions
- Examining brain images to discover which areas are active during the obsessive and repetitive behaviors of autism
- Continuing to investigate the link between thimerosal and autism
In the next section, we'll look at how autism is typically identified in children.