People with ASD tend to have thinner cortices and reduced surface area of the brain during adolescences and adulthood while they often have increased cortical development (greater expansion of the cortical surface area) in early childhood (Ha, et. al., 2015).
Individuals with ASD tend to have differences in cortical folding which is how the cerebral cortex is able to grow in size and increase in complexity. This process is essential to the evolution of the mammalian brain especially in humans (Llinares-Benadero & Borrell, 2019). This process just seems to happen differently in individuals with ASD.
Cortical gyrification is related to expansion of the outer cortical layers. It has to do with how the folds of the cerebral cortex that develop assist with the functioning of the individual (Ronan & Fletcher, 2014).
Youth with ASD tend to have enlarged gyrification of the frontal lobe compared to typically developing peers. Specific forms of gyrification, or cortical folding, may actually be associated with intelligence and cognitive abilities (Gregory, Kippenhan, Dickinson, Carrasco, Mattay, Weinberger, & Berman, 2016).
Cortical gyrification changes across the lifespan of the individual with ASD. Both genetic and environmental influences can impact the structure of cortical regions of the brain.
ASD is characterized by deficits in social communication and social interaction. Social and communication skills are experienced in particular parts of the brain.
In youth with ASD, the right inferior frontal gyrus (RIFG) which has to do with the executive functioning skill of response inhibition (Hampshire, et. al., 2010), functions differently than typically developing peers.
Additionally, the bilateral temporal regions are more highly activated as compared to typically developing peers. The temporal lobes are the primary center for processing hearing, speech, memory, smell, sensations, emotions, and behaviors. When someone has an impairment in the bilateral temporal lobe, they are often confused, have altered states of consciousness, and may not be able to recall memories as well (Eran, Hodes, & Izbudak, 2016).
Children with ASD often have to utilize greater response effort to interpret social communication input including to be able to comprehend language spoken to them from other people which may provide support for why they have to utilize more energy from the RIFG and the bilateral temporal regions.
These brain regions are also more highly activated in part due to the effort it requires of individuals with ASD to interpret the intentions and messages expressed by another person’s language.
Children with ASD may be able to attend to social cues but it requires more effort to access parts of the brain that help them to do so.
Being able to recognize facial expressions and to interpret body language and nonverbal communication is essential for fluent and effective social interactions. However, these skills may be impaired in individuals with ASD.
Additionally, individuals with ASD are often less impacted by social interactions as a form of positive reinforcement. For instance, simple gestures like smiling or nodding one’s head to show interest and approval may not reinforce the behavior of individuals with ASD as much as it would for individuals without ASD.
The differences that individuals with ASD experience in the are of social skills could be related to how they analyze facial expressions, their response with the natural mirror neuron system that is present in most people but not as strong in individuals with ASD. The mirror neuron system is a group of specialized neurons that “mirrors” or imitates the behavior of other people. The mirror neuron system is involved in social cognition, language, empathy, and theory of mind (Rajmohan & Mohandas, 2007).
The presence of restricted and repetitive behaviors, interests, or activities is linked to differences in activity of the striatum which plays a role in reward during social interactions, integrates social information, and helps reinforce social bonding (Báez-Mendoza & Schultz, 2013).
Hypo-activity in brain regions such as the STS (which is related to theory of mind and speech processing) occurs in individuals with ASD as related to displaying RRBs.
All children and adults benefit from having the ability to monitor and adjust their own behavior to accomplish specific goals. When children with ASD make errors or engage in a situation that could benefit from them correcting their own behavior, they experience increased activity in the anterior medial prefrontal cortex (mPFC) which is impacted by the focus of one’s attention and the left superior temporal gyrus (STG) which helps to process and interpret sounds including spoken words and noises (Koshino, et. al., 2011).
To continue learning about brain anatomy of autism spectrum disorder, read Part 1 or Part 3.
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