It is common knowledge that autistics and non autistics (allistics) are neurologically different. Autism is a neurological difference that is part of the neurodivergent spectrum.
After seeing this TikTok, it really inspired me to look further into this and look at the research literature.
Their heart was in the right place but obviously do not understand research study reports and just wanted to prove how different autistic brains are to allistic brains.
Her largest mistake was saying that the neurons are very different. It’s not that the neurons are different, there is a large number of neurons and the brain architecture is different in an autistic brain contrasted to an allistic one. The pathways and synapses are different but the cells are very similar, structurally.
Neuron of Autistics vs Allistics and Synapses Between Them
In a study at University of California at Davis released a study on March 3, 2023. They studied the genetic difference in brain neurons in autistic people at different ages and compared them to neurotypical neurons.
Initial excess and over connectivity of neurons may make the brain more vulnerable to early aging an inflammation which may lead to further changes in the brain structure and function. Understanding how the brain in a person with autism changes through life will provide opportunities for early intervention
Cynthia Schumann, professor of neuroscience in the Department of Psychiatry and Behavioral Sciences at UC Davis and affiliated with their MIND Institute
Method
This study analyzed brain tissues from 27 deceased autistic people and 32 allistic people. The age range of all donors were from 2-73 years old.
All brain tissues were taken from the superior temporal gurus (STG) region. The STG is an area of the brain that is responsible for sound and language processing and social perception.
The STG plays a critical role in integrating information. It helps provide meaning about our surroundings. Despite its importance, it remains relatively unexplored. We wanted to understand how the molecular changes in this critical part of the brain are happening in autism
Dr,. Cynthia Schumann
In addition to examining brain tissue, they also isolated neurons using laser capture micro dissection techniques. They studied mRNA expression on a molecular level in the STG tissue and the isolated neurons. The mRNA translates the DNA code into instructions the cells can understand and synthesize proteins for different functions in the body.
Findings
Over the course of this study, the researchers identified 194 significantly different genes between the two different neurologies. Of those genes identified, 143 produced more mRNA and 51 produced less (downregulated) mRNA than in typical brains.
These downregulated genes were linked to brain connectivity. This means that the number of synapses in autistic neural tissues differs greatly from neurotypical tissue.
This means that there is too much activity in the neurons that may cause brain to age faster in autistic people. This means more synapses.
There is also more mRNA heat shock proteins in autistic brains. These proteins respond to stress and activate immune response and inflammation.
Age Related Findings
This study also uncovered 14 genes in the STG tissue that showed age development differences between autistic and allistic people. It also showed three genes in isolated neurons. These genes were connected into synapses and immunity/inflammation pathways.
This study also uncovered an age related decrease in the gene expression involved in Gamma-aminobutyric acid (GABA) synthesis. GABA is an amino acid that helps slow down the brain.
GABA is known for producing a dampening effect in controlling neuronal hyperactivity in anxiety and stress. Our study study showed age dependent alterations in genes involved in GABA signaling in brains of people with autism.
Boryana Stamova, associate professor in the Department of Neurology and affiliated with the MIND Institute.
There was also findings that showed direct molecular level evidence that insulin signaling was altered in the neurons of autistic people. There was a significant similarity of mRNA in the STG region betweeen those with Alzheimer’s disease and autistic people. This could indicate a comorbidity.
Personal interjection:
It may be similar between the relationship between ADHD and Parkinson’s disease. Both conditions are caused by a lack of dopamine.
Although the activity and gene expression is different in autistic neurons than allistic neurons, they are structurally the same. They just lack GABA that is responsible for slowing brain activity down.
The Architecture of the Autistic Brain Vs the Allistic Brain
As described by Psycom, the structure of the autistic brain is hard to describe. It is easier to describe the differences between the autistic and allistic brain.
Anatomy of the Human Brain and Differences between the two neurologies
Autistic Brains Differ Before Birth
According to a study that was published on August 24, 2020, shows that the development of brain cells en utero differ even though a diagnosis does not happen until much later. The autistic development starts at the early stages of brain organization. This happens at the cellular level.
This study was published in Biological Psychiatry and was ran by scientists at Kings College London and Cambridge University in the United Kingdom.
In this study we used induced pluripotent stem cells, or iPSCs, to model early brain development. Our findings indicate that brain cells from autistic people develop differently to those from typical individuals.
Deepak Srivastava PhD from the MRC Centre for neruodeveopmental Disorders and Department of Basic and Clinical Neuroscience at Kings’s College London, supervised the study.
The researchers in this study isolated hair samples from nine autistic people and six typical people. They treated the cells with various growth factors. The scientists were able to influence the hair cells to become neurons. These neurons were similar to those found in the neurocortex or midbrain region. IPSCs retain the genetic identity of the person from where they were taken from and the cells restart their development just like it would happen en utero. This allowed for people to watch early brain development.
Using iPSCs from hair samples is the most ethical way to study early brain development in autistic people. It bypasses the need for animal research. It is non invasive and it simply requires a single hair or skin sample from a person.
Dwaipayan Adhya PhD, a molecular biologist at the Autism Research Centre in Cambridge and Department of Basic and Clinical Neuroscience at King’s College London.
During different stages, the researchers examined the developing cells. They were trying to see the appearance and they sequenced their RNA. This was to see which genes the cells expressed.
By day 9, the developing neurons from typical people formed neural rosettes. They are intricate dandelion like shape that indicated typically developing neurons. Cells from autistic people formed similar rosettes or did not form them at all. Key development genes were expressed at lower levels in the autistic cells.
By days 21 and 35, cells from typical and autistic people differed substantially. This suggested that the makeup of neurons in the cortex differs in the autistic and typically developing brain.
The emergence of differences associated with autism in these nerve cells sows that these differences arise very early in life.
John Krystal, PhD, Editor in Chief of Biological Psychiatry
Cells directed to develop as midbrain neurons- a brain region not associated with differences in autistic people, showed only a slight difference between typical and autistic people.
The use of iPSCs allows us to examine more precisely the differences in cell fates and gene pathways that occur in neural cells from autistic and typical individuals. These findings will hopefully contribute to our understanding of why there is such diversity in brain development.
Dr. Srivastava
The Brain Hemispheres
Let’s not assume that everyone is familiar with the anatomy of the human brain. The brain is split down the middle into two parts called hemispheres. This is where the terms right brain and left brain come from.
The right brain and left brain thinking is a myth. Cognitive processes ping pong back and forth between the two halves of the brain.
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
Doctor Jeffery Anderson, MD PhD, professor of radiology and the University of Utah.
In recent research, science discovered that the hemispheres in autistic brains are slightly more symmetrical than the allistic brain. The small amount of asymmetry is not enough for diagnosis. This is according to a report in Nature Communications. How this symmetry comes into play is still being researched. When science is updated, this will also be updated.
Here what has been proven. Left-right asymmetry is an important aspect of brain organization. Some brain functions have a tendency to be dominated (lateralized), by a side of the brain.
One example of this is speech and comprehension. In allistic brains are 95% right hander and 70% of left handers, speech and comprehension is processed in the left hemisphere.
In autistic people, there is a tendency to have reduced leftward language internalization. This may be why there is a higher rate of being left handed in the autistic community compared to the allistic community.
The Lobes of the Brain
Inside the two hemispheres there are lobes. They are the
- frontal
- parietal
- occipital
- temporal
Inside the lobes, there are structures that are responsible for everything from movement to thinking and beyond.
On top of the lobes, there is the cerebral cortex which is made up of grey matter. This is where the information processing takes place. The different wrinkles in teh brain add to the surface area of the cerebral cortex. The more surface area of grey matter, the more information can be processed. Almost like a hard drive. Only the brain can keep growing, a hard drive cannot.
The grey matter has peaks (gyri) and troughs (sulchi). Researchers at San Diego University have researched these structures and found that these structures develop differently in an autistic brain. Autistic brains have significantly more foldings in the left parietal and temporal lobes. This is also true for the right frontal and temporal lobes.
These alterations are often correlated with modifications in neuronal network connectivity. In fact, it has been proposed that strong connected cortical regions are pulled together during development, with gyri forming in between. In the autistic brain, the brain reduced connectivity, known as hypo connectivity, allows weakly connected regions to drift apart with sulci forming between them
Dr Lorenza Cultta, PhD , post doctoral fellow at Northwestern University/s Feinberg School of Medicine, Center for Autism and Neurodevelopment
With all this information, autism still is a mystery to researchers.
One thing that has become a more recent observation is that 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. It may be the timing of the brain activity that’s abnormal, that the signals from one region of the brain to another get blurred in time. And the results of that is the brain is more stable in autism and it’s not able to move between different thoughts or activists as quickly or as efficiently as someone without autism.
Dr. Anderson
These structural differences are not evident in every autistic person. There have been some trends that have emerged in a subset of autistic people.
Hippocampus
It has been shown with MRI imaging that autistic adolecents and children have an enlarged hippocampus. This is the area of the brain that is responsible for forming and storing memories. Several studies have replicated this finding. It is not clear if this difference is still evident into adulthood.
Amygdala
The size of the amygdala also differs between autistic and allistic people. Researchers from different labs have had conflicting results. Some of them find that autistic people have a smaller amygdala than allistic people. Others say they are only smaller if the autistic person also has anxiety.
There are other researchers who say that autistic children have enlarged amygdalae early in development and that the differentce level off over time.
Cerebellum
Autistic people have a lower amount of brain tissue in parts of the cerebellum. This is the brain structure at the base of the skull. This is according to meta analysis of 17 imaging studies.
Researchers thought that the cerebellum mostly coordinates movements, but they now know that it plays a role in cognition and social interactions, too.
Neocortex
The outer layer or the brain, or the neocortex, seems to have a different pattern of thickness than those who are allistic. The difference is consistent with the alterations to a single type of neuron during development, according to a 2020 study.
How the Autistic Brain Functions Differently Than the Allistic Brain
The connections, or synapses within a brain are what makes it function. It’s the neurons that act as 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
Researchers measure these impulses by looking at how synchronized regions of the brain are. When these regions are working together, they have a higher rate of having brain activity at the same time. Functional connectivity is the measurement of how much two regions of the brain seem to be synchronized or communicating with each other.
When comparing the connectivity of the autistic brain, researchers have observed some networks with lower connectivity, especially in patterns where distance between brain regions is greater.
In autism there’s short range over connectivity and long range under connectivity. So, for tasks that require us to combine or assimilate information in different parts of teh brain, like social function and complex motor tasks, individuals with autism have more trouble. And when there’s a very specific task focused on 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.
Dr Anderson
The connections are only as good as the neurons carrying the impulse through the cell bodies to other neurons. Neurotransmitters are the chemical messengers.
It is thought that the differences described above may cause the traits of autistic people but it has not been proven. Dr. Anderson warns that it is hard to know exactly what brain connection correlates to what sign.
According to scientific research, white matter, the bundles of long neuron fibers that connect the brain regions, is also altered in autistic people. The structure of white matter is studied by using a diffusion MRI. This measures the flow of water throughout the brain.
People who lack all or part of one white matter tract, called the corpus callosum, connects the two brains halves, have an increased chance of being autistic or having autistic traits.
Correlation does not mean causation. It is important to keep that in mind when reading research literature.
Autism and Aging
Autistic people are born with autistic brains and it is a life long disability. Many traits and brain patterns do become similar to allistic brains with age, but development is very complex and should not be over simplified.
For example, 20% to 30% of autistic people do develop seizure disorders, such as epilepsy. It is not understood why, it is just a comorbid condition.
There are also mental health conditions such as anxiety, depression and obsessive compulsive disorder. This is more prevalent in the autistic community than the allistic community.
The world can benefit from the autistic brain and scientific research is starting to see this.
Many people with autism don’t see it as a disorder. They may see it as a gift. Society generates enormous benefits from individuals with autism. They’re good at tasks that are really important to society. And I think its important to always emphasize that its in society’s best interest to help create environments where people with different brain structures and ways of behaving can thrive.
Dr. Anderson
Sources:
https://www.psycom.net/autism-brain-differences
Brain structure changes in autism, explained
https://www.sciencedaily.com/releases/2020/08/200824091958.htm
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4688328/
Aviva Seigler 