connected neuronsDuring infancy, the brain grows a large number of synapses to facilitate communication between brain regions. As a child ages, a typical brain prunes many of these synapses to prevent the brain from becoming overwhelmed by stimuli. Research from Columbia University Medical Center finds that, for children and adolescents with autism spectrum disorders, the brain does not carry out this synaptic pruning as it does for young people without autism. The glut of synapses may be responsible for deficits in social and sensory processing among people with autism.

The researchers analyzed samples of brain tissue from children and adolescents who died between ages two and 20. Half of the children had autism, but the rest did not. The researchers examined a part of the brain’s temporal lobe that is associated with social behavior and communication. To find out whether young people with autism had more synapses, the researchers counted spines. Spines are tiny neurons that receive synaptic signals.

Children with autism have more spines than children without autism. In young children, autistic and non-autistic brains have comparable amounts of synapses. A typically developing 19-year-old has 41% fewer synapses than a typically developing toddler. However, older teens with autism have only 16% fewer synapses than young children with autism. This suggests that pruning synapses, not over-production, is a problem for people with autism. The researchers also identified biomarkers and proteins in the autistic brains that indicate problems with autophagy, the process of clearing out old cells.

The research team conducted a similar trial using mice with abnormal social behaviors. The mice had a hyperactive protein, called mTOR, that inhibited the brain’s autophagy processes. The researchers found that a drug could reduce the number of excess synapses in the mice’s brains. After the drug treatment, the mice no longer exhibited abnormal social behaviors.

This research adds to the scientific understanding of how autism develops after childhood. The research could help explain why people with autism are oversensitive to noise and other stimuli.

This research is published in the journal Neuron.

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