Using primarily MRI, researchers have found that people with ASD have certain brain areas that are a different size or that are located in a different position compared with the control cohort. The implication of this is that some components of the behavior of a person with ASD are a direct result of having a certain brain area that is bigger or smaller than what is found in the control cohort.

In the past decade, the DTI technique has been used to study interconnections between brain areas in people with ASD. These studies have found dozens of brain areas where the interconnecting links appear to be compromised in people with ASD compared with the control cohort. In some cases, the “damage” to these tracts in the brains of people with ASD has been compared experimentally with brain damage caused by a stroke or other traumatic brain injury. These types of studies imply that even if all brain areas appear normal, their ability to communicate with one another may be compromised in people with ASD.

The functional activity of brain areas is typically measured while a person is performing a specific task. For example, ASD is characterized by an inability to recognize a person’s emotional state based on facial expressions. As a result, many tests involve measuring the activity of brain areas while a person looks at images of emotionally charged faces. Several studies have found that when a person looks at images of angry faces, the amygdala (an area of the brain) has a much higher level of activity in people in the control cohort than in people with ASD. These types of studies attempt to identify what type of information each specific brain area is processing.

With the MRS technique, the amount of certain chemicals in brain areas can be measured. These types of studies measure the amounts of different types of neurotransmitters and compare the levels between people with ASD and a control cohort. An example of a result from this type of study is a finding that a specific brain area produces more of an inhibitory neurotransmitter in people with ASD than in a control cohort. Such a result suggests that in people with ASD that brain area may be of the correct size and may be connected properly to the other brain areas but is sending the wrong type of message to the rest of the brain.