Autism is now recognized as a varied group of developmental disorders, known as autism spectrum disorders or ASDs. It is defined at the behavioral level, and its three hallmark features are known: impaired social interaction, communication difficulties and repetitive behaviors.

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 children with autism have too many nerve fibers, but that they’re not working well enough to facilitate communication between the various parts of the brain.

Brain imaging techniques, such as magnetic resonance imaging (MRI), have been used to examine the brains of individuals with autism. However, results have been inconsistent. Abnormal brain areas in people with autism include the:

• Cerebellum – reduced size in parts of the cerebellum.
• Hippocampus and Amygdala – smaller volume. Also, neurons in these areas are smaller and more tightly packed (higher cell density).
• Lobes of the Cerebrum – larger size than normal.
• Ventricles – increased size.
• Caudate nucleus – reduced volume.

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.

Additional resources to help understand Autism and the brain