“It’s been a hot topic over the last few years that autism’s cause is rooted in the mirror neuron system because of the difficulty people with autism have with social interaction and understanding the behavior of others. But there hadn’t been a thorough and precise test of that theory. We wanted to really investigate the system, and our research dispels the theory that it causes autism. This is important because now scientists can focus on alternative ideas,” said Marlene Behrmann, Carnegie Mellon University professor of psychology and director of the Cognitive Neuroscience Lab, who used brain imaging techniques to help produce this pivotal result.
To evaluate the integrity of the mirror neuron system in autism, Behrmann and her colleagues asked adults with and without autism to observe and execute a series of hand movements while being scanned with functional magnetic resonance imaging (fMRI). The fMRI measurements allowed the research team to infer the strength of neural responses in mirror system areas of each group during observation and execution of the same movements. Earlier behavioral and neuroimaging studies that reported weak mirror neuron system responses in individuals with autism did not address the issue of movement-selectivity and in that sense, did not offer a targeted test of the mirror neuron system hypothesis.
Behrmann and her team found that the mirror system areas responded normally for autistic individuals — the brain showed the identical response when the same movement was observed and when that same movement was executed. In addition, the location and strength of the brain responses were equivalent for the individuals with autism and their matched controls.
The mirror neuron system consists primarily of two brain areas with unique characteristics — each area is active when the individual executes a movement, like grasping a cup of coffee, and when the individual observes someone or something else moving. Previous research suggested that when something is observed, the neurons simulate the movement, helping the brain to process the movement’s meaning, such as recognizing someone picking up a coffee mug. For the simulation process to work properly, neurons within the mirror system must recognize select movements and represent each unique movement in terms of a different pattern of cortical activity.
“By using the most precise imaging technology available and advanced statistical and analytical procedures, we found that there is no difference between the mirror system responses of individuals with autism and those without,” Behrmann said. “There is clearly more work to be done to understand autism, but we’ve paved the way for the direction of that future research.”
In addition to Behrmann and her former graduate student, Cibu Thomas, and former post-doc, Kate Humphreys, the research team consisted of Ilan Dinstein, former graduate student at New York University and now a postdoctoral fellow at the Weizmann Institute in Israel, David Heeger from New York University and Nancy Minshew from the University of Pittsburgh.
The study was funded by grants from the National Institutes of Health, Cure Autism Now and the Pennsylvania Department of Health.
For more information, watch a video of the research team discuss the study.
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