On the surface we are aware of differences between autistic people’s brains and non-autistic people based on behaviors. People with autism have difficulty communicating, socializing, and understanding more abstract concepts. They also perseverate and use repetitive motions, often called stimming. An autistic person is usually much more visual, a factor that guides how they are taught language and most tasks. The reason for this has to do with brain differences between autistic and non-autistic people.
Brain Differences and Autism: The Cerebellum
People with autism have a larger cerebellum and a smaller corpus callosum. These areas of the brain control attention and communication within the brain. This size difference was first noticed by Dr. Joseph Piven from the University of Iowa. The smaller corpus callosum makes communication from the front of the brain to the back more difficult.
Dr. Joseph Piven stated in the American Journal of Psychiatry, "The expected size relationships of various parts of the brain to one another seems to be disproportionate or distorted in autism…This makes you think that those areas might be disconnected functionally."
The larger cerebellum also has a reduction in the number of Purkinje cells, which contain serotonin. Serotonin is responsible for mood, and inhibition.
Brain Differences and Autism: The Limbic System
The Autism Research Institute published the findings of Dr. Stephen Eldeson PH.D, Dr. Margaret Bauman, (Dept. of Neurology, Harvard Medical School), and Dr. Thomas Kemper, (Depts. of Neurology, Anatomy, and Pathology, Boston University School of Medicine) regarding the structural differences of an autistic person's limbic system.
The amygdala which is generally associated with the regulation of emotions, aggression and is linked to responding to sensory stimuli is smaller in an autistic person. When this is removed from an animal they will avoid eye contact and their fight or flight response is more triggered. A removed amygdala in an animal forces them to be aggressive and the inference drawn from this is that a smaller amygdala could be why some autistic people have aggressive episodes.
The hippocampus, which is also smaller in an autistic brain, controls much of a person’s ability to respond to stimuli. When it is removed from an animal self-stimulatory behavior is more prevalent, and therefore being smaller in an autistic brain could be the reason why we see similar behavior in people with autism.
Brain Differences and Autism: Visual Abilities
Autistic brains are more wired for visual abilities. After collating 15 years of data from over 700 brain images (357 autistic, and 370 non-autistic) researchers at the University of Montreal's Centre for Excellence in Pervasive Development Disorders determined more activity in the temporal and occipital regions which are the areas which control vision and long term memory. They also noted less activity in frontal cortex. The frontal cortex runs our reward system and planning abilities.
Autism Research Insitute:Autism and the Limbic System, Dr. Stephen Eldeson https://www.autism.com/pro_page.asp?PID=304
University of Montreal (2011, April 5). Autism: Exceptional visual abilities explained. ScienceDaily. Retrieved April 22, 2011, from Science Daily https://www.sciencedaily.com/releases/2011/04/110404093149.htm
Bryn Mawr College, The Analysis of Autism Facilitates Neuroanatomical Investigations, Karen Taverna. Retrieved April 21,2011 From Serendip. Brynmawr EDU.
Colstate College, Pinal Gland and Melatonin, Retrieved April 21, 2011 https://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html
Louisville University News, Brain structure differences may explain nature of autism, July 6th, 2006, Retrieved April 21, 2011https://php.louisville.edu/news/news.php?news=638
Berwichshire News, Scans Find Autistic Brain Changes, April 22, 2011, Retrieved April 22, 2011 https://www.berwickshirenews.co.uk/news/health/behind-the-headlines/scans_find_autistic_brain_changes_1_401875