Autism is a disorder of the brain that affects how people with the condition interact with others and the world around them. Autism’s effects on the brain vary greatly depending on the individual as well as the severity of the disorder.

Autism is not a static condition. It occurs on a spectrum, with severe impairment on one end and a high level of functioning on the other. People with severe autism often do not speak very much; in some cases, they are completely nonverbal. They can have debilitating intellectual and cognitive impairments.

On the other hand, some people with high-functioning forms of autism have average IQs, even above average IQs, and can communicate verbally. Despite certain strengths, they may struggle to read nuance, body language, sarcasm, or subtext.

People with autism generally struggle in social situations. Their interests in certain topics can appear to be obsessive, to the exclusion of other interests and interactions with other people. When they become overwhelmed, they often perform repetitive behaviors to soothe themselves. Sometimes, these behaviors can be disruptive or even dangerous.

The Autistic Brain

A postdoctoral fellow at the Center for Autism and Neurodevelopment at Northwestern University’s Feinberg School of Medicine explained to PsyCom in “The Autistic Brain” that because autism has multiple causes (including environmental factors, genetic attributes, and comorbid neurological and mental conditions), it is difficult to fully assess the effects that the disorder has on the brain.

Simply looking at the brains of people with autism to determine what’s different — and how those differences can be predicted, managed, or even “fixed” — will not yield easy answers. Even with imaging techniques revealing some measurable differences, there are obstacles to fully distinguishing an autistic brain from a brain without autism, with the right amount of sensitivity and specificity to offer a diagnosis or prognosis.

Neuroanatomy of Autism

Even the “neuroanatomy of autism” can defy description, so talking about the structure of the brain tends to reveal more about how autism affects it.

To begin with, the brain is split into two hemispheres (halves), from which we understand the concepts of the left brain and the right brain. In reality, however, thinking and cognitive processes tend to be shared between the two hemispheres. In the brain of an autistic person, the connection between the two hemispheres is not as fluid as it is in the brain of a

neurotypical person. Communication is not as strong.

Recent research has found that the hemispheres of brains with autism spectrum disorder are slightly more symmetrical than neurotypical brains, but this difference is not enough to diagnose autism. Furthermore, how the symmetry can lead to the development of autistic symptoms is not yet known.

What is known is that the typically asymmetrical nature of the left and right brain hemispheres is necessary for brain organization. Some functions of the brain are naturally dominated by a particular side of the brain. Key to this discussion are the processes of speech and understanding.

In most people (95% of right-handed people and 70% of left-handed people), speech and understanding are worked out in the left hemisphere. However, those with autism tend to have impaired leftward language dominance, which might be why people with autism are usually left-handed as opposed to the general population.

Autism & the Lobes of the Brain

Additionally, within each hemisphere of the brain, there are four lobes: the frontal, parietal, occipital, and temporal lobes. Within these lobes are structures that control everything the body does, from movement to thinking. On top of the lobes is the cerebral cortex, where information processing takes place.

The greater the surface area of the cerebral cortex, the more information the brain is capable of processing. The brain has folds, to add to the surface area of the cerebral cortex. Researchers at San Diego State University have found evidence that suggests that the folds develop differently in people with autism. In autistic brains, there is much more folding in some of both the left and right lobes.

The changes have been connected to modifications in network connectivity in neurons. The weaker a connection, the deeper the folds are. Other research has indicated that language production and processing are altered.

Yet, says PsyCom, the neurobiology of an autistic brain is still hidden. Some experts have said that the more they study brains affected by autism, the more they realize that “it may not be so much about the hardware [of the brain] as the software.” It may be that the timing of the brain activity is different, affecting how the signals from one region of the brain being sent to another get distorted. It might be that as the autistic brain ages, the aging process brings about more changes that impact the development of autistic symptoms.

Processing Information

Other research has uncovered that people who have autism spectrum disorder have brains that receive and process information differently than neurotypical people. Research has shown that autistic brains have less coordinated activity, but it is not known whether individual brain regions also work differently.

The brains of people with autism process information differently than those of people without autism. The brain, as a whole, shows less coordinated activity in autism, for example. But whether individual brain regions also work differently in autism is unclear.

A 2017 study published in eLife noted that in people who have autism, the sensory areas of their brains displayed much more random activity than the brains of neurotypical people. The more severe the presentation of autism, the more random the activity. Researchers suggested that people with autism have brains that cannot store and process sensory input in the same way and for the same amount of time that non-autistic brains can.

The 2017 study also noted that the caudate, a brain region that is responsible for storing and processing memories (using data from past experiences to guide future behavior, which is important in the development and application of language) responded in the opposite way for people with autism. The activity in that region was much more predictable in the brains of autistic people. The more a person had inflexible, repetitive behaviors, the more the caudate activity in their brain conformed to predictable patterns. This is likely because changes in the structure of individual brain regions drive the differences in the randomness of neural activity.

Magnetic Stimulation

The researchers behind the eLife study posited that when small brain regions undergo changes in their activity and structure, these changes are what leads to the development of complex autism symptoms. Understanding these changes in the brain can possibly help doctors diagnose autism much earlier in a person’s life.

It is not yet known whether the differences in the brain activity directly cause the symptoms of autism or whether they simply correlate to autistic symptoms. If there is a direct relationship between brain activity and autism symptoms, the researchers suggested that it might be possible to change brain activity (via magnetic stimulation to the scalp) to potentially reduce the severity of the symptoms.

Other studies have also suggested transcranial magnetic stimulation (TMS) to ease the symptoms of autism. Even though initial investigations have been promising, scientists have noted that “there is simply not enough evidence to conclusively support the clinical widespread use of TMS in ASD.” This limitation also extends to other forms of treatment that try to address the effects autism has on the brain.

Brain Connections

Other researchers have offered additional theories on the effects of autism on the brain. Quoted in Medical News Today, a professor of radiology at the University of Utah Health speculated that the brains of autistic people “are not as efficient at rapidly shifting between ideas or thoughts,” leading to autistic people becoming distressed at unexpected stimuli or changes in routine and patterns. This difficulty with change is a common symptom of autism spectrum disorder.

Not unlike the researchers in the eLife study, the professor and his colleagues (who had their findings published in JAMA Network Open) learned that for people with autism, the circuits in their brain were subjected to “overly persistent brain connections.” Using a novel fMIR method to look at brain activity, the researchers at Utah discovered connections exist for longer than they do for neurotypical people (up to 20 seconds). The result of this extended period of connectivity is that the brain cannot easily switch between processes. Additionally, people on the autism spectrum showed an increase in the severity of their symptoms when the connectivity of their brain’s circuits occurred for this extended duration.

The lead author on the study paper concluded that autistic people who struggle with greater levels of social dysfunction “have an increase in synched activity in their scans.” However, the researchers only worked with male study participants, and there is no indication whether female autistic individuals will have the same brain patterns and responses.

Increased Miscommunication for Autistic Brains

“Too many brain connections may be at the root” of autism was Science Daily’s summary of a study from the Washington University School of Medicine. Researchers found a defective gene that influenced how neurons connect to and communicate with each other. Studies on animals that lacked the gene also showed too many connections existing between those key brain neurons and difficulties with learning and memory.

The findings led the Washington University researchers to suggest that the symptoms of autism may be the result of problems in how cells in the brain communicate with each other — specifically that “there may be too many synapses in the brains of patients with autism.” The senior author of the study explained that instead of more synapses making the brain work better, the higher number results in increased miscommunication between neurons. This leads to impairments with learning, but the mechanisms of this problem aren’t fully understood.

The Brain & Genes

Many genes have been connected to autism, but six genes attach ubiquitin, a molecular tag, to proteins. These genes tell the rest of the cell what to do with the tagged proteins, such as discard them, move them to another part of the cell, or increase or decrease activity. People with autism might have a mutation that stops one of the ubiquitin genes from functioning as it should. Again, it is not known how problems with tagging proteins affect the circuitry and operation of the brain to the point that it leads to the development of autism.

Part of the researchers’ work involved animal studies, where the ubiquitin gene was removed from the cerebellum of young mice. In humans, the cerebellum is one of the key regions of the brain that is affected by autism. It is responsible for voluntary movements like speech, coordination, balance, and motor control, but it also plays a role in higher cognitive functions, like attention and language. People on the autism spectrum often have delayed language development and hyper-focused interest on single topics, to the point of not paying attention to anyone or anything else around them.

Understanding the Complicated Effects of Autism

Other research has also supported the theory that “abnormalities of the cerebellum [...] are associated with autism.” A study published in Frontiers in Systems Neuroscience posited that impaired circuitry activity in the cerebellum could partially underlie symptoms of autism, including but not limited to restricted motor functioning and cognitive deficits, specifically with regard to attention span, language development, and executive functioning.

If much remains unknown about autism’s effects on the brain and if what is known appears patchy or even contradictory, it is because “autism spectrum disorder is complicated,” says PsyCom. Even as experts answer some questions about what autism does to the brain, there are further questions raised about other effects, how these effects lead to the development of autism symptoms, and even broader questions about the full scope of the functioning of the human brain itself.

As more and more research is dedicated to the subject, we’ll continue to uncover more about autism’s effects on the brain.

References

The Autistic Brain. (May 2020). PsyCom.

Why People With Autism Have a More Symmetrical Brain. (November 2019). Neuroscience News and Research.

There Are Indeed More Left-Handers Within the Autism Spectrum Disorder Compared Within the General Population, but the Many Mixed-Handers Is the More Interesting Finding. (September 2018). Journal of Autism and Developmental Disorders.

Brains of Children with Autism Show Unusual Folding Patterns. (July 2018). Scientific American.

How Does Autism Affect the Brain? (February 2019). eLife.

Use of Transcranial Magnetic Stimulation in Autism Spectrum Disorders. (February 2016). Journal of Autism and Developmental Disorders.

What Does Autism Look Like in the Brain? (November 2018). Medical News Today.

In Autism, Too Many Brain Connections May Be at Root of Condition. (November 2017). Science Daily.

Perturbed Proteostasis in Autism Spectrum Disorders. (2016). Journal of Neurochemistry.

Is Autism a Disease of the Cerebellum? An Integration of Clinical and Pre-clinical Research. (May 2013). Frontiers in Systems Neuroscience.

Effects of Age on Brain Volume and Head Circumference in Autism. (July 2002). Neurology.

Big Brains May Hold Clues to Origins of Autism. (February 2016). Spectrum.

Visual System May Offer Glimpse of Autism’s Effects in Brain. (October 2016). Spectrum.

Brain Immune Cell Defect May Help Explain Social Impairments in Males With Autism. (April 2020). Scripps Research.

Brain Study Finds Evidence That Autism Involves Too Many Synapses. (August 2014). Autism Speaks.