Scientists may be one step closer to unlocking the mystery of autism's origins. According to a new study published in the Journal of the American Medical Association, autism may be linked to an excess of neurons in a child's brain. "For the first time, we have the potential to understand why autism gets started," says Eric Courchesne, the study's author and a professor of neuroscience at the University of California, San Diego. Here, a guide to the findings:

How was this study conducted?
In order to comb extensively through brain tissue, researchers could only examine postmortem specimens. Thus, the study was small: The brains of seven deceased autistic children were compared with the brains of six deceased kids who didn't have autism, says David W. Freeman at CBS News

And what did they find?
The autistic kids "had, on average, 67 percent more neurons — a type of brain cell and a building block of the nervous system — than boys without autism at a similar age," says Jennifer Goodwin at USA Today. These neurons were concentrated in the prefrontal cortex, which "is key to complex thoughts and behaviors, including language, social behavior and decision-making." The brains of autistic children were also found to be heavier, weighing an average of 17.5 percent more than the brains of kids without autism. 

What does it mean?
Neurons are only generated during development in the womb. Thus, this study lends compelling evidence to the argument that autism has a prenatal origin — and is not something triggered during early childhood. "For the first time, we have something really solid," says Courchesne. The extra neurons in autistic kids equate to a "huge increase in potential connections and, therefore, a potential for miswiring, which would lead to abnormal function."

How will this discovery help the fight against autism?
In the future, brain size could "have a large impact on future autism screening." Pediatricians, for instance, might flag children with abnormally large brains as potential victims of the disease earlier than they do now, and be able to start treatment sooner.

Sources: CBS News, Fox News, USA Today