Everyone’s brain is structured slightly differently based upon genetic composition and changes that occur in the life experiences of the individual.
However, in general, there are some overall similarities in the human brain such as certain parts of the brain being for specific purposes or where particular regions of the brain are located.
Diagnoses Are Often Associated with Differences in Brain Functioning
When a diagnosable disorder is present, the brain may have some differences compared to most people in the general population.
This could be due to a genetic predisposition for the brain to be structured in a particular way or it could be due to operant conditioning – learning from life experiences that shape the brain’s structure including neuronal connections and functioning in various parts of the brain.
ASD and Neurobiology of the Brain
In general, individuals with autism spectrum disorder have certain characteristics in the neurobiology of their brain including in the way that the brain is structured, how it functions, and the connectivity present within the brain.
Everyone’s brain may change in some ways across the lifespan. This is the same for individuals with ASD. Their brains may change in structure, function, or neuronal connectivity across their lifetime.
Total Brain Volume – Size of the Brain is Bigger in Younger Children with ASD
In early childhood, from approximately two to four years of age, children with ASD are found to have accelerated brain volume growth as compared to children without ASD. Children with ASD often have greater brain volume when they are young but then do not show differences in brain volume when they are older as compared to typically developing peers (Ha, Sohn, Kim, Sim, & Cheon, 2015).
The increased brain volume in young children with ASD seems most commonly associated with differences in the volume of the frontal lobe, which has to do with motor movements and language as well as executive functioning and attention (Chayer & Freedman, 2001) and the temporal lobe which has to do with auditory, olfactory, vestibular, visual and linguistic functioning (Kiernan, 2012).
When youth with ASD enter their adolescent years, they may experience less differences in brain volume as compared to typically developing peers. So, from around age ten to fifteen, children with ASD don’t have as much difference in brain volume growth.
Brain volume differences in youth with ASD may be due to accelerated surface area growth of the cortical region of the brain, which is the outermost part of the brain.
Brain Structures in Individuals with ASD
Parts of the brain that are associated with the characteristics identified in the diagnostic criteria for autism spectrum disorder include the following.
THE FRONTAL LOBE
The frontal lobe has to do with executive functioning skills like working memory, inhibition, attention, language, and emotion (Hoffman, 2013). See the image below for the location of the frontal lobe in the brain. The green area in the image is considered the frontal lobe. This is the area of the brain closest to the forehead.
© Frontal Lobe by Kenhub; Illustrator: Paul Kim
THE TEMPORAL LOBE
The temporal lobe helps to process sensory information and incorporate sensory input into meaningful memories, language, and emotions. The temporal lobe includes (Patel & Fowler, 2019):
- the superior temporal gyrus (which helps to process and interpret sounds including spoken words and noises)
- the superior temporal sulcus (STS; which has multiple functions depending on the neuronal connections it is engaged with including theory of mind and speech processing; Hein & Knight, 2008)
- wernicke’s area (which processes written and spoken language)
- the amygdala (which helps to manage emotions)
- the hippocampus (which helps to create memories)
See the image below for the location of the temporal lobe in the brain. The green area in the image is considered the temporal lobe.
© Temporal Lobe by Kenhub; Illustrator: Paul Kim
THE FRONTOPARIETAL CORTEX
The frontoparietal cortex has many functions one of which is to help us estimate time and manage time which is important for daily functioning and social interactions (Hayashi, et. al., 2018)
THE ORBITOFRONTAL CORTEX
The orbitofrontal cortex (OFC) is involved in motivational behavior, social behavior, and emotional behaviors (Rolls, 2004).
THE CAUDATE NUCLEUS
The caudate nucleus may be related to stereotypic behaviors, motivational behaviors, perseverative behaviors, and obsessive-compulsive type behaviors (Villablanca, 2010).
THE BASAL GANGLIA
The basal ganglia has to do with motor control and physical behavioral coordination (Lanciego, Luquin, & Obeso, 2012).
THE ANTERIOR CINGULATE CORTEX
The anterior cingulate cortex plays an important role in processing social information (Apps, Rushworth, & Chang, 2016).
THE INFERIOR FRONTAL GYRUS
The inferior frontal gyrus (also known as Broca’s area) helps us to produce language, comprehend language, and may even contribute to non-verbal motor movements such as hand movements or sensory motor integration (Binkofski & Buccino, 2004).
THE PARIETAL CORTEX
The parietal cortex is related to many cognitive functions including the activity of selective attention (Behrmann, Geng, Shomstein, 2004).
Interactions of the Various Brain Regions in ASD
There are many complex interactions within the brain of all human beings. In ASD, the way in which different parts of the brain may interact with each other may be somewhat different than typically developing individuals.
For example, the structure and functioning of Broca’s area, the STS, and Wernicke’s area may be associated with the social language processing and social attention behavioral characteristics often seen in individuals with ASD.
Another example is how the frontal lobe, the superior temporal cortex, the parietal cortex, and the amygdala could be related to how individuals with ASD manage social situations differently than typically developing peers.
The way that the OFC and caudate nucleus function in individuals with ASD is associated with restrictive and repetitive behaviors common in this population.
To continue learning about brain anatomy of individuals with autism spectrum disorder: See Part 2.
Ha, S., Sohn, I. J., Kim, N., Sim, H. J., & Cheon, K. A. (2015). Characteristics of Brains in Autism Spectrum Disorder: Structure, Function and Connectivity across the Lifespan. Experimental neurobiology, 24(4), 273–284. doi:10.5607/en.2015.24.4.273
Kiernan J. A. (2012). Anatomy of the temporal lobe. Epilepsy research and treatment, 2012, 176157. doi:10.1155/2012/176157
Hoffmann M. (2013). The human frontal lobes and frontal network systems: an evolutionary, clinical, and treatment perspective. ISRN neurology, 2013, 892459. doi:10.1155/2013/892459
Patel A, Fowler JB. Neuroanatomy, Temporal Lobe. [Updated 2019 Jan 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519512/
Hein, G; Knight, R T (2008). Superior temporal sulcus – It’s my area: or is it? Journal of Cognitive Neuroscience, 20(12):2125-2136.
Hayashi, M. J., van der Zwaag, W., Bueti, D., & Kanai, R. (2018). Representations of time in human frontoparietal cortex. Communications biology, 1, 233. doi:10.1038/s42003-018-0243-z
Lanciego, J. L., Luquin, N., & Obeso, J. A. (2012). Functional neuroanatomy of the basal ganglia. Cold Spring Harbor perspectives in medicine, 2(12), a009621. doi:10.1101/cshperspect.a009621
Apps, M. A., Rushworth, M. F., & Chang, S. W. (2016). The Anterior Cingulate Gyrus and Social Cognition: Tracking the Motivation of Others. Neuron, 90(4), 692–707. doi:10.1016/j.neuron.2016.04.018