The Science Behind Autism
There is an enduring question that presents itself while studying psychology: the argument of nature versus nurture. What factors actually cause a condition? Are they biological or social? It also applies to ASD; is autism attributed to genetics or the environment? The answer is actually both. In this article, we’ll examine the “nature” component.
Let’s first examine the biological, specifically genetic, components of ASD. Everyone’s genetic code is different. A genetic mutation is a change that occurs in a DNA or RNA sequence when duplicating for cell division and synthesizing proteins. They can be harmful, beneficial, or have no effect. There are four main types of mutations: substitution, deletion, insertion, and translocation. DNA structure consists of two linked strands forming a double helix shape. Each strand has a backbone made of alternating deoxyribose and phosphate groups. Attached to each deoxyribose is one of four nitrogenous bases: adenine, thymine, guanine, and cytosine. DNA mutations have to do with a change occurring to the nitrogenous base, whether guanine is substituted for adenine, a thymine is deleted, or a cytosine is added. Research has been done on specific genes that may lead to autism if mutated, such as ACTL6B. In RNA-binding proteins, mutations that disrupt binding sites may also contribute to autism; these include missense mutations, where a single amino acid is different, or nonsense, where an amino acid acts as a stop codon and makes the protein too short. Both of these are due to point mutations in the DNA.
How do these mutations affect brain development? The answer lies in neuroscience. It is difficult to tell apart an autistic brain from a brain without ASD, so imaging techniques are not primarily used for diagnosis. According to Jeffrey S. Anderson, professor of radiology at the University of Utah, “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”.
The brain is split into two hemispheres, known as the right and left brain, which communicate and send signals between each other to facilitate function. In an autistic brain, there is some difficulty in the communication between the two hemispheres, with not as many strong connections. Furthermore, scientists have recently found that ASD brains have slightly more symmetry than non-ASD brains. How this symmetry plays into autism traits is still being researched, but there is a popular theory concerning the lateralization of the brain. Left-right asymmetry is an important aspect of brain organization as certain functions pertain to a specific atmosphere; the left brain is more responsible for language and reasoning while the right brain concerns creativity and spatial skills. Autistic people tend to have reduced leftward language lateralization, which may also explain why they have a higher rate of being left-handed compared to the general population.
Within each hemisphere of the brain, there are four lobes: frontal, parietal, occipital, and temporal. On top of the lobes lies the cerebral cortex, a thin layer of gray matter, where information processing occurs. The folds in the brain add to the surface area of the cerebral cortex, and more surface area allows for more information processing. Gray matter ripples in peaks called gyri and sulci respectively, but in autistic brains, these deep folds may develop differently. With ASD, there is significantly more folding in the left parietal and temporal lobes, as well as the right frontal and temporal lobes. Strongly connected cortical regions are pulled together during development, with gyri forming in between. But in the autistic brain, hypoconnectivity allows weakly connected regions to drift apart and form sulci between them. The deeper these sulcal pits are, the more language production is affected. Even the tiniest difference in the folds can present itself differently in terms of cognition skills, demonstrating the true breadth of the spectrum.
