Introduction


"Autism is a polygenetic developmental neurobiologic disorder with multiorgan system involvement, though it predominantly involves central nervous system dysfunction" (Minshew). Just in the United States, 1 in 68 children are diagnosed with autism spectrum disorder (ASD)1. As these numbers have drastically increased through the years, they require a closer inspection of the autistic brain. Currently, there are many theories in the psychology attempting to determine the cause of such an increase in numbers.

The concept of talking about an autistic brain is a complicated because of its stark differences with a normal brain. The molecular analysis of an autistic brain reveals that 75% of people with autism have a common brain defect2. There is an even more difficult in conceptually understanding autism: autistic brain themselves can be very different from one another. This phenomenon is what causes savants, in which individuals with Autism pursue a profound skill.

Anatomical Review

Major brain structures.png
The autistic brain includes abnormalities such as increased total brain, parieto-temporal lobe, and cerebella hemisphere volumes. Additionally, the amygdala, hippocampus, and corpus callosum are also different in size. There is also evidence of irregularities in neural network involving the front-temporal parietal cortex, limbic system, and cerebellum3 . However, it is important to note that other studies have not been able to show abnormalities in these regions.

There has been proof Purkinje cell loss, located in the cerebellum4. The Purkinje cells, an immense inhibitory cell, receives information from the parallel fibers and climbing fibers. Deficiency of such cells can be manifested behaviorally as difficulties with impulsivity3.

For children with autism, through the use of fMRI the results have shown that they have less activation in the deep parts of the brain responsible for executive functioning. As a result, the caudate in the basal ganglia receives receives less activation, mostly in autistic boys 5. This can highly influence the prefrontal brain and all of its critical functions.


Function Review


Much of the research done in autistic brains have revealed an imbalance in the pathology of excitatory and inhibitory neurons5. Autism implicates numerous genes that are significant for preserving excitatory/inhibitory balance. There is also a common deficit in neocortical PV-cells, which are part of the inhibitory system.

Individuals with autism usually report high variability in visual acuity. The binocular visual system often contains anomalies, such as strabismus, with a percentage of 21-84% of the autistic population studied3. This can result and/or add to sensory confusion for Autistic individuals since the visual input they receive is constantly changing. Deficiency in smooth pursuit and saccades has also been shown in ASD patients. Smooth pursuit is affected by either being poor pursuits or poor fixation6.The saccades of an Autistic individual are either hypometric or have reduced velocity. The saccadic abnormalities indicate that there may be functional disturbance in the cerebellar vermis or/and the fastigial nuclei. When Autistic people produce guided saccades they show increased activation of the dorsolateral prefrontal cortex, caudate nucleus, medial thalamus, anterior and posterior cingulate cortex, and right dentate nucleus3. These systems have to compensate for the lower-level visual motor systems which are in disturbance, thus resulting in smooth pursuit and saccade abnormalities. Individuals with autism are said to not process face recognition as normal brains do. Face recognition, which is a function of the ventral cerebral cortex, is not processed in the same way indicating anomalies in the visual processing as well.

Cortical connectivity is lower for an autistic brain compared to a normal brain. In the autistic brain, high local connectivity may develop alongside low-range connectivity as a result of widespread alterations in synapse elimination and/or formation7. Also, high physical connectivity and low computational connectivity can reinforce one another through the failure of differentiating signal from noise.

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(Belmonte, source 7)


When studying brain connectivity of autistic brains, researchers focus on the left middle frontal, left superior parietal, and left middle occipital. While fMRI results showed patterns in these areas similar to a normal brain, they were more extensive in the autistic brain. As a result, there has been suggestive deficits in task-specific network connections8. According to the Functional magnetic resonance imaging of autism spectrum disorders, "Compared to the control group, autistic subjects showed the following: (1) less connectivity between the posterior cingulate cortex and superior frontal gyrus and (2) more connectivity between the posterior cingulate cortex and both the right temporal lobe and right parahippocampal gyrus. Weaker connectivity between the posterior cingulate cortex and the superior frontal gyrus in autistic subjects was correlated with poorer social functioning, and stronger connectivity between the posterior cingulate cortex and right parahippocampal gyrus was correlated with behaviors that were more restricted and repetitive (Dichter)."


Pathways


There is evidence for an increase in pathway volume and fiber number even in the absence of increased total brain volume.
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Cognitive pathway involved in face processing in typical adult subject (A) and in an adult with autism (B); (Minshew, source 9)


There is not much difference of the input and output pathways between a normal and autistic brain. Although there are various deficits in the connectivity of the brain, the ascending tracts to the motor cortex and descending tracts to the spinal cord are the same as a normal brain.


Conclusion


There are many deficits found in the autistic brain beyond the ones listed here. Included deficits are more physiologically focused, versus psychologically or behaviorally. The deficits often include talents that can be used in favor of an autistic individual. Currently, since the causation of this disorder is not clear, there is no cure and little treatment is known. Doctors/parents/teachers have learned how to interact with autistic children/adults, but have not yet found a medication that can control all the symptoms. Since there is an enormous increase of cases, researches are working more diligently to understand autism.


Glossary


  • Autism: a mental condition, present from early childhood, characterized by difficulty in communicating and forming relationships with other people and in using language and abstract concepts
  • Savant: a condition in which a person with a mental disability demonstrates prodigious capabilities or abilities far in excess of what would be considered normal
  • Visual acuity: sharpness of vision, measured by the ability to discern letters or numbers at a given distance according to a fixed standard
  • Strabismus: abnormal alignment of the eyes; the condition of having a squint
  • Smooth Pursuit: eye movement that allows eye to follow a moving object
  • Saccades: a rapid movement of the eye between fixation points


Quiz

(All questions asking about the autistic brain)

True and False:

  1. The cerebella hemisphere volume does include an abnormality when compared to a normal brain. T/F
  2. Purkinje cell is not an inhibition cell that affects impulsivity. T/F
  3. To all the places that guided saccades show increase in activation, the thalamus is not one of them. T/F
  4. Cortical connectivity is lower. T/F
  5. There is suggestive deficits in specific networking connections. T/F

Short Answer:

  1. How is autism connected to strabismus?
  2. Based on this reading, how is the cerebellum affected?
  3. What are the major brain structures implicated in autism?

Suggested Readings


- What is Autism Spectrum Disorder? - article goes in depth about what is autism, who is at risk, how to live with it, and clinical trials.
http://www.nimh.nih.gov/health/topics/autism-spectrum-disorders-asd/index.shtml
- Multimodal brain imaging in autism spectrum disorder and the promise of twin research. -article discusses some key complex interactions of genetic and environmental factors impacting the autistic brain.
Mevel, K., Fransson, P., & Bölte, S. (2015). Multimodal brain imaging in autism spectrum disorder and the promise of twin research. Autism: The International Journal Of Research & Practice, 19(5), 527-541. doi:10.1177/1362361314535510

References:


1. DeNoon, D. J. (2011). Autism brains alike; very different from normal brains. WebMD. Retrieved from: http://www.webmd.com/brain/autism/news/20110525/autism-brains-alike-very-different-from-normal-brains
2. Falco, M. (2014). Autism rates now 1 in 68 U.S. children: CDC. CNN. Retrieved from: http://www.cnn.com/2014/03/27/health/cdc-autism/
3. Viola, S. G., & Maino, D. M. (2009). Brain Anatomy, Electrophysiology and Visual Function/Perception in Children within the Autism Spectrum Disorder. Optometry & Vision Development, 40(3), 157-163.
4. Courchesne E, Press G, Yeung-Courchesne, R. Parietal lobe abnormalities detected with MR in patients with infantile autism. Amer J Roent 1993:160(2):387-393
5. Hensch, T. K., & Bilimoria, P. M. (2012). Re-opening Windows: Manipulating Critical Periods for Brain Development. Cerebrum: The Dana Forum on Brain Science, 2012, 11.6. Rosenthall U, Johansson E, Gillberg C. (1998). Oculomotor findings in autistic children. The Journal of Laryngology & Otology ,102(5):435-439.7. Belmonte, M. K., Allen, G., Beckel-Mitchener, A., Boulanger, L. M., Carper, R. A., Webb, S. J. (2004). Autism and abnormal development of brain connectivity. The Journal of Neuroscience, 24(42): 9228-9231. doi:10.1523/JNEUROSCI.3340-04.2004. 8. Dichter, G. S. (2012). Functional magnetic resonance imaging of autism spectrum disorders. Dialogues in Clinical Neuroscience, 14(3), 319–351.9. Minshew, N. J., & Williams, D. L. (2007). The New Neurobiology of Autism: Cortex, Connectivity, and Neuronal Organization. Archives of Neurology, 64(7), 945–950. http://doi.org/10.1001/archneur.64.7.945

Answers to Quiz Questions

True and False:

  1. T
  2. F, it is an inhibitory cell
  3. F, medial thalamus
  4. T
  5. T

Short Answer:

  1. The binocular visual system often contains anomalies. These anomalies can be considered strabismus, which is the abnormal alignment of the eye.
  2. Through Purkinje cell loss, which provides inhibitory input.
  3. Cerebral cortex, basal ganglia, amygdala, hippocampus, corpus callosum, cerebellum, and brain stem.