KIDS
September 5, 2014

Pruning the Hedges of Autism

“Neural pruning” helps kids' brains become more efficient. This happens less among children with ASD. Here's why.

Autism spectrum disorders may be the result of an overgrown garden of neurons in the brain, according to findings by a team at Columbia University. Neurons are the cells in our brain responsible for processing and transmitting information. They form networks of branch-like projections that connect with neighboring cells — up to 500 trillion connections to be exact.

The fact that we can see changes in behavior suggests that autism may still be treatable after a child is diagnosed.

These connections undergo a process of pruning during development, much like you'd prune a rose bush or garden hedge. This pruning process reduces the overall number of connections which streamlines transmission, leaving a more efficient configuration behind, so mental processing is faster.

This pruning occurs much more slowly in the brains of children with autism spectrum disorders (ASD), resulting in far higher numbers of connections between neurons, the neuroscientists found. This could help explain why many children with ASD can be overwhelmed by noise and changes to their routines.

More importantly, the researchers have found that a drug, rapamycin, that restores normal synaptic pruning can improve autistic-like behaviors in mice. It does this even when it is given after the behaviors have emerged.

Rapamycin has serious side effects and though these might prevent its use in children with autism, the finding is an important discovery on the path to finding effective treatments.

“The fact that we can see changes in behavior suggests that autism may still be treatable after a child is diagnosed, if we can find a better drug,” senior investigator, David Sulzer said in a statement.

During infancy, there is a burst of connections between neurons, particularly in the cortex, a brain region involved in autistic behaviors. By late adolescence, many of these connections have been eliminated by pruning. Researchers observed a 50% reduction in connections in healthy children, compared to only 16% in autistic children.

“It's the first time that anyone has looked for, and seen, a lack of pruning during development of children with autism,” Dr. Sulzer said.

The inefficient pruning in mice seems to be the result of an overactive protein, mTOR, the researchers discovered. Large amounts of overactive mTOR can also be found in almost all of the brains of the autism patients studied, and the same processes may occur in children with autism.

“What's remarkable about the findings is that hundreds of genes have been linked to autism, but almost all of our human subjects had overactive mTOR,” said Dr. Sulzer, “and all appear to have a lack of normal pruning. Overactive mTOR …may be a unifying feature of autism.”

The study is published in Neuron.

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