To test the idea that autistic brains prune less than normal brains, co-author Guomei Tang, assistant professor of neurology at CUMC, measured synapse density in the brains of deceased autistic children, including 13 brains from children ages two to nine, and 13 brains from children ages 13 to 20. Twenty-two brains from children without autism were also examined for comparison.
Tang measured synapse density in cortical brain tissue samples by counting the tiny spines that extend from neurons. In the control brains, she found that the density of the spines dropped by about half. In the autistic brain samples, they were reduced only by 16 percent.
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Taking the research a step further, the team then examined the brains of mice to try and trace the pruning defect. They zeroed-in on a protein called mTOR, which, when overactive, inhibits the brain's self-trimming ability.
"While people usually think of learning as requiring formation of new synapses, the removal of inappropriate synapses may be just as important," the study's senior investigator, David Sulzer, professor of neurobiology in the Departments of Psychiatry, Neurology, and Pharmacology at CUMC, explained in a press release.