Recently, researchers at San Diego State University researchers may have decided the winner of an ongoing battle between competing theories of autism spectrum disorder. This disorder, often referred to simply as autism, actually describes a wide range of individuals with social deficits communication problems and repetitive behaviors . Autism has puzzled researchers since Leo Kanner first described it in 19431. Most individuals with autism have normal IQ’s and extremely variable levels of social deficits2. These social deficits can range from the inability to use and understand language at all, to having trouble holding reciprocal conversations with others. While there are countless theories as to what causes the social deficits in autism, two are emerging as frontrunners.
|Children with autism often prefer to play alone instead of with other children.|
Photo from Simons Foundation Autism Research Initiative
One theory of autism is the Mind Blindness Theory. According to this model, the social deficits in Autism Spectrum Disorder are caused by dysfunction in the area of the brain that is responsible for abstract processing of other’s intentions3. This area of the brain is crucial to understanding and interpreting the words and actions of others. Being able to infer another person’s mental state is known as Theory of Mind. Imagine you are in your friend’s house on a chilly fall day, and you are uncomfortably cold. You notice the window is open and say “It sure is cold in here today.” Your friend walks over to the window and closes it. Your friend has just used Theory of Mind to interpret your statement as a request to close the window. A person with Autism may respond to your statement by agreeing that it is cold, not understanding that your statement was actually a request for them to get up and close the window.
The other theory of autism is based on dysfunction of the Mirror Neuron System. In the area of the brain that initiates movement, such as picking up a fork, there are neurons that will also fire the exact same way in response to someone else picking up a fork. Before the discovery of mirror neurons, it was thought that neurons in the area of the brain responsible for initiating movement had only that one specific purpose. Some scientists believe that these neurons that fire to initiate action as well as fire in response to other people performing actions help people to understand the actions of others. It is hypothesized that there is problem with these neurons in Autism, leading to problems interpreting the actions of others4.
So which theory was declared to be the winner? Both. The results of the study described below showed that not only are there problems in both systems, but the communication between the two systems seems to be different in adolescents with autism.
Inna Fishman and her colleagues were interested in examining what differences in brain connectivity they could find in adolescents with autism, and how these differences in brain connectivity translate into social impairment. In other words, they were attempting to determine if a higher degree of abnormality in the brains of individuals with autism would manifest as more severe social impairment5.
Fishman technique called fcMRI (functional connectivity magnetic resonance imaging) which measures the way the brain is connected while a person is at rest. The study included 25 adolescents (ages 11-18) with autism and 25 adolescents without autism.
The results of the study showed evidence of less connectivity in the Theory of Mind brain region in those with autism compared to those without autism. Less connectivity suggests that the individual neurons in this section of the brain are not communicating with the neurons around them in a typical manner. In other areas associated with the Theory of Mind processes they found an increase in connectivity, which has been shown by other researchers. These results provide support for the Mind Blindness Theory of autism.
The most significant finding by Fishman was the increase in connectivity between the Theory of Mind system and the Mirror Neuron System. Further, in a subset of the sample, the amount of connectivity was correlated with higher levels of social impairment. Adolescents with autism who had the greatest amount of connections between the two brain areas also had the most severe social deficits. Fishman and her colleagues have hypothesized that both the Mirror Neuron System and the Theory of Mind portion of the brain are not function normally in people with autism, which leads to increased connectivity and communication between the two areas in order to make up for the dysfunction taking place in each of the two areas.
|This figure highlights the areas of heightened connectivity between the Theory of Mind and Mirror Neuron brain areas.|
Image from Fishman et al.
While this is certainly an exciting new development in autism research, it is important to understand the limitations of this study. Given that this was an imaging study that looks at the brain after the onset of the disorder, we cannot claim causality. It is not possible to determine whether the differential connectivity causes the social symptoms, or if the increased connectivity develops as a result of dysfunction in the Mirror Neuron system and brain regions involved in Theory of Mind processing. With these limitations in mind, it appears as though both scientists studying the Mind Blindness Theory and the dysfunction of the mirror neuron system may be on the right track to solving a piece of the autism puzzle.
1. “Autism at 70-From Kenner to the DSM-5,” What We’ve Learned About Autism. September 2013. Autism Speaks. Retrieved from https://www.autismspeaks.org/science/science-news/autism-70-–-kanner-dsm-5
2. “Autism Fact Sheet” November 2014. National Institute of Neurological Disorders and Stroke. Retrieved from http://www.ninds.nih.gov/disorders/autism/detail_autism.htm
4. Dapretto, M. et al. Understanding emotions in others: mirror neuron dysfunction in children with autism spectrum disorders. Nat. Neurosci. 9, 28–30 (2006)