Discover SPARK

Understanding Autism, Understanding the Brain

Marina Sarris

Date Published: October 21, 2019

Many scientists say that the key to understanding autism lies within the brain. How and why does the brain work differently in people who have autism? Will learning more about brain function lead to better treatments?

“The human brain is really a wonderful, amazing computer designed to process information and ultimately lead to behavior,” explained neuroscientist David G. Amaral in a 2018 presentation about brain research in autism.1 Autism is diagnosed by behavior, namely social communication symptoms and repetitive behaviors.

Autism researchers use different methods to study the brain, a complex system of billions of nerve cells and trillions of connections. Some scientists use Magnetic Resonance Imaging, also called MRI, to scan the brains of people who have autism. Other research involves studying brain tissue from people who have died, looking for changes at the level of a brain cell.

Brain Scans and Autism

MRI scans can produce images of people’s brains while they are resting, watching a video, or playing a game, for example. The scans can show changes in blood flow in the brain that indicate which brain region is active at a particular time. MRI studies have revealed some differences in brain function between people who have autism and people who don’t.

For example, neuroscientist Kevin Pelphrey, Ph.D., has used MRI scans to see how children who have autism responded to social information, such as watching human movement or motion. His research team found that, in autism, the parts of the brain involved with awareness of other people’s motions did not activate as expected.2 Boys in particular did not seem as attuned to human movement.

Other MRI studies have found differences in the brains of boys and girls who have autism. The Autism Brain Imaging Data Exchange makes it easier for researchers to share and access scans for autism studies.

When comparing boys who have autism with boys who don’t, researchers found differences in the brain networks involved with the perception of people and social situations, Pelphrey said.3 That is not surprising, given that social communication challenges are a core symptom of autism spectrum disorder (ASD).

However, researchers found something different when comparing the MRI scans of girls who have autism to girls who do not. In the girls with autism, the MRI scans differed in the areas involved with emotion regulation and anxiety, which are not usually considered central to ASD.

Among those diagnosed with autism, boys outnumber girls by about 4 to 1. Males have been studied more than females because their numbers are greater.

Using MRI studies, researchers at the University of California Davis MIND Institute found other differences between boys and girls who have autism. They discovered larger brains than expected in a subset of preschool-aged boys with “regressive autism.” These boys had lost some of their developmental skills, or regressed. But the researchers did not find enlarged brains in the preschool-aged girls with autism.4

“We would like to know what causes the brain to be too big,”1 said Amaral. He leads the MIND Institute’s recruitment and research efforts for SPARK, and directs the Davis Autism Center of Excellence at UC Davis.

Studying Brain Cells

Brain scans, while very valuable, can take science only so far in understanding the genetic and cell differences in the brain tissue of people with autism. That’s because they cannot show a brain cell, or neuron, Amaral said in the 2018 presentation. The smallest piece of information visible on an MRI is about 50,000 neurons.1

To look at individual cells, he said, scientists need to examine post-mortem brain tissue. Amaral directs Autism BrainNet, which collects and distributes brain tissue donated for autism research. Autism BrainNet is funded by the Simons Foundation Autism Research Initiative, which also funds SPARK.

In one example of brain tissue research, researchers from the University of California system studied the amygdala, a part of the brain involved in social and emotional behavior, including fear.

The research team, led by Cynthia M. Schumann, Ph.D., found that the number of brain cells in the amygdala increased from birth to adulthood in typically developing people, but not in people who have autism.5 Scientists want to know how that relates to anxiety and other conditions in people who have autism.

“The hope for all of this research is that ultimately we will have better targets for the treatment of autism,” Amaral said.1


  1. Amaral D.G. Recorded webinar, Brain Tissue Research (2018)
  2. Kaiser M.D. et al. Proc. Natl. Acad. Sci. USA 107, 21223-21228 (2010) PubMed
  3. Pelphrey K.A. Recorded webinar, Girls with Autism Can Illuminate Novel Treatments (2016)
  4. Nordahl C.W. et al. Proc. Natl. Acad. Sci. USA 108, 20195-20200 (2011) Article
  5. Avino T.A. et al. Proc. Natl. Acad. Sci. USA 115, 3710-3715 (2018) PubMed