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gewg_ writes:

Autism Support Network reports

As a baby's brain develops, there is an explosion of synapses, the connections that allow neurons to send and receive signals. But during childhood and adolescence, the brain needs to start pruning those synapses, limiting their number so different brain areas can develop specific functions and are not overloaded with stimuli.

Now a new study suggests that in children with autism, something in the process goes awry, leaving an oversupply of synapses in at least some parts of the brain.

[...]

The study, published [August 21] in the journal Neuron, involved tissue from the brains of children and adolescents who had died from ages 2 to 20. About half had autism; the others did not.

The researchers, from Columbia University Medical Center, looked closely at an area of the brain's temporal lobe involved in social behavior and communication. Analyzing tissue from 20 of the brains, they counted spines -- the tiny neuron protrusions that receive signals via synapses -- and found more spines in children with autism.

The scientists found that at younger ages, the number of spines did not differ tremendously between the two groups of children, but adolescents with autism had significantly more than those without autism. Typical 19-year-olds had 41 percent fewer synapses than toddlers, but those in their late teenage years with autism had only 16 percent fewer than young children with autism.

The original article is behind NYT's paywall.