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Brain Activity and Autism

By Kiersten Miller

A person’s brain with autism has many functioning parts, but there are some areas that differ greatly in these people versus neurotypical people. It has been knowledge for a long time about the “inner world” an autistic person can sometimes be observed to be in.  Scientists in 2014 found that children with autism have high levels of brain activity when in a nonactive, resting state compared to other children. This could explain the “withdrawal into self” theory. The testing of this theory was completed at the University of Toronto and Case Western Reserve University, and they found that the overall brain activity was 42% higher in the brains of children on the autism spectrum in resting periods.  Autistic children and adults are more reluctant to social interactions and this might be due to the fact that their brains generate more information during times they are at rest. Along with their difficulty managing social interactions being affected, autistic people have a difficulty interpreting facial expressions. In a neurotypical person, their amygdala, a region in the frontal lobe of the brain, is the part that identifies facial emotions and appropriately responds to the emotions of others. This part of the brain is under-active in people with autism.  The amygdala is a region filled with androgen receptors that during gestation bind to fetal testosterone. High levels of fetal testosterone is shown to reduce social skills, but can also help with attention to detail which could explain why autistic people have such a remarkable attention to details. The amygdala and the white matter of the brain in an autistic person have abnormal growth rates in their microstructure. In early years of life, the regions grow abnormally fast and then hit a plateau and slow the growth rate compared to a neurotypical child. This makes those regions dysfunctional at integrating significant information. Approximately one-third of autism patients are macrocephalic, having an exceptionally large head and excess brain growth.  This excess brain tissue alters neural pathways and synaptic channels in the brain. The enlargement of the brain is most commonly seen in the frontal lobe of the cerebrum, but the occipital lobe, a region in the posterior region of the brain, is most times normal sized.  In brains that are developing autism, the neurons are not connected in the right ways especially in regions associated with language and social cognition. It is not that there is a lack of neurons or that they are placed in the wrong areas, these neurons are just not functioning in the proper way. This disconnection of the neurons is not the only detachment found in the brain. There is a disconnect between the brain and the outside stimuli, which results in the inability for the brain to change based on what it integrates about the outside environment, this is called abnormal plasticity.  Neurotypical people shape their brain as they go through “critical periods” or “sensitive periods” of their life. These are developmental windows where the environment has the most influence on the brain circuitry. The periods are timed differently for the different brain regions and functions. During these periods, essential brain development is formed and without the correct timing certain functions can be disrupted. When the brain has a higher level of normal plasticity, during the early years, the brain typically has the correct ratio of excitatory and inhibitory neural signals that allows for brain development during these special periods. Excitatory signals are ones that can effectively travel down the axon to the postsynaptic neuron and produce a reaction. Inhibitory signals impede the neurons’ ability to propagate a signal from its synapse to the postsynaptic neuron.   In a brain with autism the ratio of these signals are not correct and so the critical period in the brain region is not triggered, thus not allowing for exact development. When a brain is developing autism, the inhibitory neural signals, especially the parvalbumin cells, do not allow for brain growth. The balance between the amount of excitatory and inhibitory synapses where the neural signals propagate through is important in establishing brain connections and in a brain that has an incorrect ratio, the effects can be devastating.  These critical periods happen around the age of two and three, so this could explain why symptoms of autism do not appear until around that age. Children are making connections in their brain from their outside environment and experiences during these early years, but these connections are not being made properly in children with autism. These patients have too many neurons in their brain affecting how they concentrate. They are aroused by outside stimuli even when asked to focus on one area of their therapy. When shifting their attention in a rapid manner, there brain overactivates because of the abnormal ratio of excitatory and inhibitory neurons. The autistic brain has too many synapses and this affects the speed at which information can be integrated. In the natural development of the brain before birth and as a baby, there is a natural pruning process that gets rid of unneeded synapses and some axons. The brain of an autistic person does not achieve this curtailing process leaving excess amounts of synapses and axons.  There are cortical connection interferences in a person with autism. There is an underdevelopment in these areas that affect task related functions. Also in the frontal-posterior cortical area of the brain there is a lack of functional ability which affects the coordinating of information to specific brain regions and reduces literacy skills. Autistic people have the inability to communicate between the brain regions as effectively as neurotypical people. The area this can be seen most is in the visual processing areas that transfer the information very slowly if at all.  The full knowledge about how the brain in an autistic person differs from neurotypical people is still not known, but much research is dedicated to a better understanding of this condition.

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