Autism Spectrum Disorder (ASD) is complicated. It refers to a host of complex neurodevelopment disorders, all of which are characterized by repetitive patterns of behavior and difficulties with social connection and interaction. These symptoms, such as the inability to make eye contact or to talk about feelings, the repeated phrases, or the overly focused attention to certain objects or subjects, begin early in childhood and continue to affect daily functioning throughout the person’s life.

“Autism has multiple causes—such as genetic factors, and environmental factors, comorbid neurological and mental conditions—such as epilepsy, intellectual disability, OCD and ADHD, and a wide range of symptomatology,” says Lorenza Culotta, PhD, a post-doctoral fellow at Northwestern University’s Feinberg School of Medicine, Center for Autism and Neurodevelopment.

If we look to the brain for answers or diagnosis, we won’t necessarily find it—at least not easily. Imaging techniques allow us to see differences that we can measure; but, it is difficult to tell an autistic brain from a brain without ASD with enough sensitivity and specificity to prognose, or even diagnose.

“The changes in the brain are subtle and we mostly see them in the average across a lot of individuals because in single individuals, just the normal differences from person to person tend to be much more dramatic than the subtle systematic changes associated with autism,” says Jeffrey S. Anderson, MD, PhD, professor of radiology at the University of Utah.

Still, science has done many comparison studies between ASD brains and brains not affected. Here’s what their findings can tell us about the structure of and the interworking of the autistic brain.

How Is The Structure Of The Brain Different?

“The neuroanatomy of autism is difficult to describe,” Dr. Culotta says. So it might be easier to talk about the architecture of the brain and how the autistic brain may differ.

So what’s different in the structure of this three-pound organ? Let’s start with a quick anatomy refresher: First of all, the brain is split into two halves or hemispheres. It is these two hemispheres that we get the idea of a left brain and a right brain. In reality, our thinking and cognitive processes bounce back and forth between the two halves. “There’s a little bit of difficulty in autism communicating between the left and right hemispheres in the brain. There’s not as many strong connections between the two hemispheres,” Dr. Anderson says.

In recent years, science has found that the hemispheres of ASD brains have slightly more symmetry than those of a regular brain. This small difference in asymmetry isn’t enough to diagnosis ASD, according to a report in Nature Communications. And, exactly how the symmetry may play into autism’s traits is still be researched.

Here’s what researchers do know. Left-right asymmetry is an important aspect of brain organization. Some functions of the brain tend to be dominated, or to use the technical term lateralized, by a side of the brain. One example is speech and understanding. For most people (95 percent of right-handers and about 70 percent of left-handers) it’s processed in the left cerebral hemisphere. People with ASD tend to have reduced leftward language lateralization, which could be why they also have a higher rate of being lefthanded compared to the general population.

The differences in the brain don’t stop there. Another quick Biology 101 review: Within each half, there are lobes: frontal, parietal, occipital, and temporal. Inside these lobes are structures that are in charge of everything from movement to thinking. On top of the lobes, lies the cerebral cortex aka grey matter. This is where information processing happens. The folds in the brain add to the surface area of the cerebral cortex. The more surface area or grey matter there is, the more information that can be processed.

Now, we’re going to get a little technical. Grey matter ripples into peaks and troughs called gyri and sulci, respectively. According to researchers from San Diego State University, these deep folds and wrinkles may develop differently in ASD. Specifically, in autistic brains there is significantly more folding in the left parietal and temporal lobes as well as in the right frontal and temporal regions.

“These alterations are often correlated with modifications in neuronal network connectivity,” Dr. Culotta says. “In fact, it has been proposed that strongly connected cortical regions are pulled together during development, with gyri forming in between. In the autistic brain, the brain reduced connectivity, known as hypoconnectivity, allows weakly connected regions to drift apart, with sulci forming between them.” Research has shown the deeper theses sulcal pits are, the more language production is affected.

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Despite all this information about how an autistic brain might be set up, its neurobiology is still a mystery. “One thing that has become a more recent observation is that it may not be just about the structure of the brain, in other words, it may not be so much about the hardware as the software,” Dr. Anderson says.

“It may be the timing of brain activity that’s abnormal, that the signals from one region of the brain to another get blurred in time,” Dr. Anderson says. “And the results of that is the brain is more stable in autism and it’s not able to move between different thoughts or activities as quickly or as efficiently as someone without autism.”

How Does It Work Differently?

The connections within a brain bring it to life. And it’s the brain cells or neurons that act as the messengers. “When a brain cell is active, it creates an electrical impulse and that gets propagated to other cells in the brain. We think that electrical activity holds the basis of thought and behavior and how the brain functions,” Dr. Anderson says.

Researchers indirectly measure these electrical impulses by looking at how synchronized regions of the brain are. When regions are working together, they tend to have brain activity at the same time. Functional connectivity is the measurement of how much two regions of the brain seem to be synchronized or talking together.

The connectivity issue

When comparing the functional connectivity of ASD brains and unaffected brains, researchers see that there are some networks with lower connectivity, especially in patterns where the distance between brain regions is greater.

“In autism there’s short-range over-connectivity and long-range under-connectivity,” Dr. Anderson says. “So, for tasks that require us to combine or assimilate information in different parts of the brain, like social function and complex motor tasks, individuals with autism have more trouble. And when there’s a very specific task focused with the single brain region that’s primarily involved—activities like paying attention to specific features in the world around us, individuals with autism tend to be quite good or even better than normal.”

Possible reasons

But these connections are only as good as the neurons carrying the message through their cell bodies to other neurons. Neurotransmitters are those chemical messengers. “In recent years, special attention has been given to the connection between neurotoxic compounds, neurotransmitters, and ASD,” says Dr. Culotta. Neurotoxins are natural or artificial substances that influence the functioning of the nervous system. Think: pesticides, insecticides and phthalate esters (which are used as plasticizers in the production of electronics, packaging and children’s toys).

“Prenatal or perinatal exposure to these chemicals is believed to affect brain development and therefore has been proposed as an etiological mechanism of autism,” she says. “The mechanisms through which the neurotoxic compounds may cause autism are still unclear. One of the proposed mechanisms is that neurotoxic compounds interfere with neurotransmitters.”

Do These Differences Impact Symptoms?

Most likely the result of these connections manifest into the signs and the symptoms that we see. However, Dr. Anderson cautions that it is hard to know exactly what brain connection correlates to what sign. “Ultimately, there’s still an awful lot that we need to know,” he says. “Just looking at that brain imaging, we aren’t really able to explain all of the behaviors that we see.”

What Happens As The Autistic Brain Ages?

ASD starts in early childhood and continues into adulthood. Many of the symptoms and the brain patterns normalize with age but, along the way, a lot of complex development takes place.

For instance, 20 to 30 percent of people living with autism develop seizure disorders. But the reason isn’t really understood. “It may just be that there’s this chicken and egg issue, or sometimes the seizure disorder can predispose them to autism, and sometimes it might be the other way around, and we really understand that link yet,” Dr. Anderson says.

Then, there are other mental health conditions that come into play. It is common for people living with ASD to also experience anxiety, depression and OCD—more so than in the general population.

One thing is for sure, society can benefit from the autistic brain. “Many people with autism don’t see it as a disorder. They may see it as a gift,” Dr. Anderson says. “Society generates enormous benefits from individuals with autism. They’re so good at tasks that are really important to society. And I think it’s important to always emphasize that it’s in society’s best interest to help create environments where people with different brain structures and ways of behaving can thrive.”

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Last Updated: May 4, 2020